Hi folks I'm trying to figure out if this power transistor can have Pin 1 completely left out of the circuit? That is... not soldered to anything? what I have here is an Italian made active stage speaker, it has 3 x LM3886's, 1 x LM317 and 1 x LM337. The LM3886's are all have a different soldering layout. It was severely hacked by the previous "tech", one of the LM3886's had been pulled out by force and he pulled all the paths along with the pins and did a fabulous job of trying to solder everything back in. I've got myself a set of new LM3886's, new LM337 and a new LM317. I have already installed and cleaned up the hacked LM3886, it was even missing one of the pins, I have also installed the LM317 and LM337 and am currently on LM3886 number 2 which has also been messed with but not so badly. The only solder point missing is on pin 1. Holding the circuit board up against the light I can see where the solder point used to be but it doesn't seem to be pathed to anything, just a solder point.
Do you think that this is normal? what would this pin usually be tied to? And yes I have asked for the schematic directly from the techs of the company that makes these speakers, but no luck whatsoever, even if the speaker is no longer made.
Any help at all would be great
thanks
J.
Hi
jimmy74, Welcome!
To avoid confusion the LM3886 is a "chip amp", not a "transistor".
According to the data sheet (http://www.digchip.com/datasheets/parts/datasheet/321/LM3886-pdf.php) this chip has two positive power supply pins, 1 and 5. I've just quickly scanned the data sheet and it seems to be mute on this topic, but if pin 1 isn't connected but pin 5 is in your amp, then this should be sufficient. This sort of thing is normally done to allow board designers some flexibility in their layouts.
Quote from: jimmy74It was severely hacked by the previous "tech", one of the LM3886's had been pulled out by force and he pulled all the paths along with the pins
Ouch! This is somebody to avoid in the future.
Quote from: jimmy74Do you think that this is normal? what would this pin usually be tied to?
Quite possibly. Supply positive like pin 5. Compare the two layouts - what do they do with pin 1 on the other one?
In most cases amps built with chip amps will simply use the suggested circuit straight off the data sheet (Fig 2, p5). As you have two of them it's a fair bet (if it's mono and not stereo) that it uses the
bridge circuit with one chip amp driving each end of the speaker (with opposite signals).
HTH
There are 3 of these chip amps:
LM3886 1 - pin 1 is tied to pin 3
LM3886 2 - pin 1 is connected to nothing (pin 5 however is soldered to something)
LM3886 3 - pins 1 and 5 are both connected separately to the board
I haven't tried turning it on yet, but before any replacements the amp was giving me very loud noise and thumps through the speaker and going to protection or peak mode. And also they had used heatsink washers that were too short allowing for the mounting screw to short the amp chip to the heatsink.
I just wanted to be sure before plugging it in.
thanks
J.
I tried turning it on, and after a couple of seconds the same thing happens as before, loud noise and the peak light tuns on. Maybe it's the caps that need to be replaces, 2 x 6800uf 63v and while I'm at it I'll change the bridge rectifier out too, what the correct replacement for a PBL403?
thanks
J.
You are just guessing. Throwing parts at the amplifier is not the way to fix it.
For example, the LM317 and LM337 are voltage regulator ICs. What led you to replace them?
Firstly the way they were soldered in, as I said the previous tech did a fantastic job of ripping out the parts and hacking the paths, the VR's were just hanging on by a blot of solder used to connect the 3 pins to what was left of the signal paths and there was some monkey business with these too. I suspect that they were (and I copied that with the new parts) put in the wrong way around but without a schematic this would be hard to verify.
what do you think?
First of all get yourself a schematic. What amplifier is it - someone here may be able to help you with it. If you dont know what you are doing then you are just going to destroy more chips.
I have been insisting on this since this active speaker was brought to me, but the distributors and techs of this brand are not willing at all to let the schematic out of their bonds for some unknown top secret reason. This brand is DB and the model is OPERA LYRIC 215. It has been discontinued so I really don't understand why they aren't willing to let the schematic go.
Quote from: tonyharkerFirst of all get yourself a schematic.
He's already tried that - see OP. They're being anally retentive. (ps see footnote and attach)
Quote from: jimmy74LM3886 1 - pin 1 is tied to pin 3
(assuming that you are counting pins from the right end - you
have downloaded the data sheet, haven't you?) this is seriously WRONG. Pin 1 is the positive supply. Pin 3 is the output - tie the supply to the output and say bye bye to your chip.
Disconnect all the speakers from the amps (if you value them).
Quote from: jimmy74I tried turning it on
DON'T power it up without a
current limiting lamp (http://www.ssguitar.com/index.php?topic=2093.0) (unless you actually
like replacing brand new semiconductors and getting nowhere fast).
Before doing anything else make one of these up because you already need it.
Quote from: jimmy74they had used heatsink washers that were too short allowing for the mounting screw to short the amp chip to the heatsink.
Eh??? Assuming that it once worked properly, this is more likely to be down to your "tech". Mounting screws in this case normally have a special insulating washer on the mounting screw.
Quote from: jimmy74Maybe it's the ...
As
@Enzo said, you're guessing. This is also known as the "blunderbuss method" and
it does not work.We use a
method:
First we diagnose,
next identify the faulty part(s),
finally we replace those, then happily play guitar into the wee small hours. This is the only method that actually works.
Randomly replacing components is not only expensive and fruitless, it also tends to
hide the original cause of the problem. I could cite you many examples of having an amp up on the bench that had been given a dose of the blunderbuss method, and you typically spend something like 90% of the repair time undoing the previous "repair" work to dig back to the original fault which then takes 10% of the time to fix. This is the reason that some techs simply refuse to touch something that has already been got at by the owner. It looks like this is already what your "tech" has done, and dropped you right in it.
Download the chip data sheet. (http://www.digchip.com/datasheets/parts/datasheet/321/LM3886-pdf.php) Are you counting the pins from the right end? Look at the application circuit Fig2/p5 and compare with what you've got. Take some clear crisp pictures (borrow a camera if you have to) of the innards in question and the general arrangement, and post here.
Remove all three new chips. Clean up the connection area to be sure no tracks are shorted together.
Power up
via the limiting lamp and check that you have something close to the correct supply voltages, +/-40V and +/-15V.
After you post a pic of the mangled track side of the board where the chip amps mount we will try, one at a time, to sort out the correct chip wiring.
And well lookie what I found at http://www.scribd.com/doc/101010269/OPERA-212-LYRIC-Schema-Elettrico (http://www.scribd.com/doc/101010269/OPERA-212-LYRIC-Schema-Elettrico) , attached. (anyone got a subscription so we can get the whole thing?)
Just signed up and downloaded the whole schematic, payed 9$ for it, but that's fair enough instead of going on in the dark!!
Here are some photos of what's under the board:
http://www.flickr.com/photos/73835524@N00/sets/72157638111984374/ (http://www.flickr.com/photos/73835524@N00/sets/72157638111984374/)
Looking at the top of the chip(where I can see LM3886T written) and counting the pins from right to left (if this is the correct way to do it) pins 1 and 3 are tied together on U7. Actually this looked quite normal to me as there is a path going from one pin to the other. Looking at the schematic and judging from what you logically say, pins 1 and 3 should not be tied together!! Factory monkey business?
thanks
J.
Photo showing pins 1 & 3 unsoldered on U7, there is clearly a track between them:
http://www.flickr.com/photos/73835524@N00/11085319253/in/set-72157638111984374/ (http://www.flickr.com/photos/73835524@N00/11085319253/in/set-72157638111984374/)
I wrote pin 5 on the photo but it's pin 3
Photo showing U8 with pin 1 floating:
http://www.flickr.com/photos/73835524@N00/11085206006/in/set-72157638111984374 (http://www.flickr.com/photos/73835524@N00/11085206006/in/set-72157638111984374)
Photo showing U9 + U10 + U5:
http://www.flickr.com/photos/73835524@N00/11085317413/in/set-72157638111984374 (http://www.flickr.com/photos/73835524@N00/11085317413/in/set-72157638111984374)
U9 + U10 have their heat plates not facing the main heatsink which is on the top of all 3 photos.
thanks
J.
Well first up you need to post the circuit here so we are all on the same page.
Quote from: jimmy74Factory monkey business?
Do you think
dB produce amps that don't work? And nobody notices? No, I don't either. The only monkey here is the "tech" between what was, and what now is. Whatever, how we got here isn't as important as finding a way back.
Before anything else - a limiting lamp.Pin 1 is indicated by a dimple on the front of the IC.
From the attached you can see that pins 1 and 5 (V+) are indeed connected.
If you follow each of the traces back from the IC pins then 1+5 should go back (along the edge of the board) to the positive end of one of the main filter caps.
The output pin 3 runs through pin 2 (No Connection) to a speaker output (2nd track from board edge). Check?
Pin 4 runs through pin 6 (N/C) to the negative end of the other mains filter cap, 3rd track in. Check?
Pin 7 should find its way back to ground/common. Check?
Pin 8 Mute connects to the other Mutes and to a 100uF slow start de-thump circuit. Check?
Pin 9 is feedback (indirectly) from the output. Check?
Pin 10 is signal input from the preamp output. Check?
As I said, remove all three IC's, clean off the excess solder, do the test above. Check?
Report back.
If the supplies are okay,
then we will put
one IC back in place (and find out if it's boofed).
My circuit fragment doesn't show U9 and U10 which I assume are regulators. If these are intended to mount on the heatsink (are they?) but they don't have their metal plates on that side, then they are in the wrong way around, and that won't be any good for their health either. I'll assume that these are the regulators for the +/-15V supply, so you also need to check that the right regulator is in the right position.
I suspect from your comments that the +/-15V won't be okay, and we will need to sort those power supplies before the output stage.
A more general pic showing the board top and how it presents to the heatsink would be helpful.
Quoteand counting the pins from right to left (if this is the correct way to do it) pins 1 and 3 are tied together on U7.
Umm... we generally count left to right. Check this data sheet for the LM3886, scroll down to the picture of the IC with pins numbered.
Yes for some reason I missunderstood Roly's statement - "assuming that you are counting pins from the right end". Anyways I am building up the light bulb limiter, do I need 100 watts? Can it be one of the modern energy saver bulbs or does it have be the good old type? I could find any old type ones at the local handy store!!
thanks
"Correct" end.
You need to start with a low power globe, 40W at most.
It must be a filament lamp, not a CFL (or LED), but mains QI downlights are suitable. Try to find the section that deals with globes for special uses such as ovens and fridges; they may be odd-looking or have a strange base, but these will be available for a while yet as electronic CFL's and LED's aren't suited to these hot and cold services. Most lighting joints still seem to stock a range of filament globes.
Well I must say that these bulbs are becoming like good old mullards, not one shop, supermarker, handy store, electronics store etc etc supply them anymore and fridge bulbs are max 25watts. I managed to find a working 40w bulb in an old box in the garage so I'll use that.
I also found an old variac (iskra brand) from the 60's I think, could this be handy too?
I'll start doing all the testing tomorrow, though I have one good question for you, before Roly posted telling me not to turn it on, I had already done so, do you think I'll need new amp chips? or do you think that they'd be fine?
thanks
J.
A 25W globe is handy too. I have a box with a collection from about 5 watts up to 100, not to mention a few duplicates just in case.
Quote from: jimmy74do you think I'll need new amp chips? or do you think that they'd be fine?
Part of what comes next is answering that question.
The game plan from here is; clean up the board and check the power supplies without power chips in.
Possibly discover the regulators are in backwards, and equally possibly boofed, sort that out as required.
Once the supplies are confirmed okay, fit one chip amp and see what happens. If it's boofed then try another, etc.
Once one position has come up okay, try another chip amp in the next.
Keep looping until we have good chips in all positions.
A Variac can be useful, but in this situation you really would need a limiting lamp as well, so perhaps better to leave the Variac as a later project for the moment.
Ok I've made the limiting lamp and I've carefully removed all the amp chips. I've done some tests for continuity as you suggested:
Check PINS 1 & 5 = OK ALL CHIPS
Check PINS 3 & 2 = OK U7 ONLY (U8 = Pin 3 to output, Pin 2 to Pin 1) ( U5 = Pin 2 to Pin 1, Pin 3 to ?)
Check PINS 4 & 6 = OK ALL CHIPS
Check PIN 7 = ARE THEY SUPPOSED TO GO DIRECTLY TO GROUND? THEY DON'T
Check PIN 8 = C54 100uf 25v ALL CHIPS
Check PIN 9 = NOT SURE EXACLY WHAT TO CHECK HERE
Check PIN 10= NOT SURE ABOUT THIS ONE EITHER.
And I've also verified that both voltage regulators are in the correct way. What's next?
Also tested the limiting lamp with the amp attached to it, on pins 1 &5 am getting 35vDC and on pins 4&6 am getting -35vDC.
thanks
J.
1)
QuotePin _x_ OK ALL CHIPS
What does this exactly mean?
2) With the simple JPG schematic posted earlier you already had all the data needed to repair this amp.
3) pull all chipamps, verify that each chipamp leg or pad is connected where it should, through a healthy track.
If any missing, repair it (small piece of wire, whatever)
4) still chipless, turn amp on through bulb limiter, measure voltage to grounf pn each ñleg of each chipamp.
Post it here.
Keep it simple: IC _x_ Pin _y_ = _z_ V (or whatever)
+/-35V looks reasonable. Please also check that you have +15V and -15V in the preamp area - that's what the regulators do.
well I started out today to try and get those voltages written down but something strange was happening, I wasn't getting any voltages anymore, I checked around the whole board and found that the ground wire had snapped off the lug on the mains plug. Fixed that and went ahead to reading voltages to each pin and each chip:
http://www.flickr.com/photos/73835524@N00/11173829406/in/set-72157638111984374 (http://www.flickr.com/photos/73835524@N00/11173829406/in/set-72157638111984374)
As for the +15/-15v readings there's some strange stuff going on here too, reading off the regulator pins I'm getting:
LM317
Pin 1 adj= -6.5v
Pin 2 out= -5.8v
Pin 3 in= 35.1v
LM337
Pin 1 adj = -32v
Pin 2 in = -36v
Pin 3 out = -34.5v
and here's the other half of the schematic:
http://www.flickr.com/photos/73835524@N00/11174186145/in/set-72157638111984374 (http://www.flickr.com/photos/73835524@N00/11174186145/in/set-72157638111984374)
Quote from: jimmy74LM317
Pin 1 adj= -6.5v
Pin 2 out= -5.8v
Pin 3 in= 35.1v
LM337
Pin 1 adj = -32v
Pin 2 in = -36v
Pin 3 out = -34.5v
hummmm ... well that ain't right. :(
{I can't see how you can have a more negative voltage on the LM317 "adj" than on the "out", however...}
You've got -5.8V where you should have +15V, and -34.5V where you should have -15V; so I'd guess that the LM337 is shorted (or the "adj" lead is open). The LM317
may not be damaged but I can't imagine it's happy with a negative voltage on its output. At this point I'd replace both, being careful to get them in the right place, the right way around.
I'm seriously annoyed with your "tech", he seems to have made matters quite a bit worse with his blundering around. :trouble
We will now have to see what other damage may have been caused to the preamp by excessive -ve supply voltage.
I've merged the two half circuits so we can have an overview of what is going on (attached).
The upper LM3886 feeds the high frequency speaker, while the lower two appear to be in a bridge configuration driving the main speaker. A "bridge" means that each amp is arranged to drive the speaker from each end in opposite directions, so doubling the signal voltage across it.
Most of the op-amps appear to be BA4560 duals and if needs be can be replaced with just about any available dual.
The BA6110 may be a different story. This is a special type of op-amp called an OTA or VCA - Voltage Controlled Amplifier, and you may have to hunt around a bit for a supplier who stocks it if you need one. Together with U3B and associated circuitry (D2, D3, D6, &c) this acts as a limiter/automatic gain control to throttle the amp back if over-driven.
First priority now is to get the +/-15V supplies correct, then we see what else might be damaged.
well I replaced both of the regulators, triple checking that both are in the right way, and triple checking for continuity to the surround components following the schematic. BTW there is some monkey business in the schematic too C48 and C49 are the other way around and so are C51 and C50, though + and -ve connections are still the same. However powering it on through the limiting lamp I first notices a very high pitch whistle and that the power led doesn't turn green as it had been doing up untill today.
Anyways here are the voltages I'm getting off the regulators:
LM317
Pin 1 adj = 35.4
Pin 2 out = 36
Pin 3 in = 36
LM337
Pin 1 adj = 2.6v
Pin 2 in = -36
Pin 3 out = 1.1
so what went wrong now? :grr
Quote from: jimmy74C48 and C49 are the other way around and so are C51 and C50, though + and -ve connections are still the same
I'm not sure what you mean by this. If the component numbering has C48/9 in swapped positions that is of no matter. If you mean these caps are in backwards, +ve and -ve swapped that's very serious. (C50 and 51 are not polarised).
Quote from: jimmy74LM317
Pin 1 adj = 35.4
Pin 2 out = 36
Pin 3 in = 36
LM337
Pin 1 adj = 2.6v
Pin 2 in = -36
Pin 3 out = 1.1
Well we now seem to have an opposite situation where the +ve regulator is shorted and pulling the -ve rail +ve.
You are "off the circuit" here, meaning that whatever problem you have will only be apparent by physical inspection of the board and components, no amount of circuit-gazing will help because there is something about your board that isn't on the circuit (such as a solder bridge between two regulator pins, broken track, dead regulator,
one of the associated resistors open circuit, esp R52, etc)
I'd pull the LM317 and see if that restores the -ve rail.
Since the LED is driven by these low voltage rails I'm not surprised that it's behaving strangely.
Quote from: jimmy74a very high pitch whistle
You do have all the power chips out, and no speakers connected?
Ok I'll try all of this tomorrow, and yes I have pulled all the amp chips out and there's no speaker attached, but I still did hear that very high pitch whistle, it lasted about 5 seconds.
As for the caps, no they're not backwards in terms of polarity, just in terms of component numbering. If you look at the photo of the board showing the two voltage regulators, the far right lug of the LM317 was soldered directly to a hanging track which was shorting with one of the lugs on that small white connector. So this time round I cut off the hanging track and connected the LM317 input lug directly to the +ve side of C46 using a piece of wire. Tomorrow I'll take it out and see if that fixes anything.
http://www.flickr.com/photos/73835524@N00/11085317413/in/set-72157638111984374 (http://www.flickr.com/photos/73835524@N00/11085317413/in/set-72157638111984374)
What a mess! :duh
Ok I pulled out the Lm317, the power led turns green and these are the voltages I'm getting:
LM317
Pin 1 adj = -23.3
Pin 2 out = -22.6
Pin 3 in = 39.1
LM337
Pin 1 adj = -36
Pin 2 in = -38.5
Pin 3 out = -37.1
what now?
You have reference voltages listed in the schematic. Input pin voltages should be -close- to 40VDC, both negative or positive. These seem to be ok, not exact 40 but close enough.
Output pin voltages are obviously incorrect. They should be about 15 VDC, negative and positive. Likewise "adjustment" pin voltages are incorrect: These should be about 1.25V below output voltages. This voltage potential is derived with the resistive divider from the output that serves as a feedback loop. Consult datasheets for further info.
So, given the readings I would check the condition of those resistive dividers as well as the condition of the regulator ICs.
can you point out which ones in the schematic are the resistive dividers?
The string of two resistors at the output of each regulator, their joining node connecting the "adj" pin of their corresponding regulator, other end connecting the common.
In other words: R54 and R52 for LM317 positive voltage rail regulator, and R55 and R53 for LM337 negative voltage rail regulator.
They are called "dividers" because the voltage at their joining node divides by the ratio of the resistances. This is basically how the voltage adjustment of the regulator works.
I bet you didn't even consult the datasheet like advised. The datasheet would have clearly explained the purpose of these resistors, how they are designed/calculated accordingly and how the regulators ICs work.
www.onsemi.com/pub/Collateral/LM317-D.PDF
www.onsemi.com/pub/Collateral/LM337-D.PDF
I've tested the 4 resistors and they all seem ok, 215r and 1.8k. I've followed the tracks making sure there aren't any shorts with other tracks or solder points in that area and all is fine. I've soldered back in the LM317 and taken the voltage readings. They are still all over the place and mostly incorrect. I think there may be another problem, that white 2 pin connector underneath the board is not shown in the schematic, well atleast I can't find it anywhere. One of its pins goes to ground and the other goes to the out pin of the LM317 regulator. Here are the new voltages:
LM317
Pin 1 adj = 34.8
Pin 2 out = 36.4
Pin 3 in = 36.4
LM337
Pin 1 adj = 9.4
Pin 2 in = -36.3
Pin 3 out = 8.1
And the power led remains red.
Quote from: jimmy74
LM317
Pin 1 adj = 34.8
Pin 2 out = 36.4
Pin 3 in = 36.4
The input is close enough, but the others clearly aren't right.
This regulator works by maintaining 1.25V across the resistor between Output and Adj, which defines the current through both resistors and therefore the output voltage.
The differential between Out and Adj is 36.4 - 34.8 = 1.6 which may be right within measurement error.
This gives an R54 current of;
I = E/R = 1.6/220 = 0.00727273 or about 7mA
7mA through R52 2k2 gives a voltage drop of;
E = IR = 0.007*2200 = 15.4 Volts, which would be about right.
But that isn't what you've got.
So first guess is that R52 2k2 isn't
actually finding its way back to ground/common because of an open resistor, dry joint, cracked track - something.
Second (less likely) guess is that the regulator is boofed.
At this point what I would do is remove it from the board and lash it up externally with 220 and 2k2 resistors and prove that it is (or isn't) actually regulating. If it is then you have a fault on the board, and if it isn't...
While you're at it I would do the same with the other regulator.
When you say ground/common you mean real ground or something else? I've tried following the schematic from the mains ground wire to D4,D5,R51 and C39 and across to CONN 11 and up to here everything seems fine. CONN 11 then meets the junction of C46 and C47 and that's fine too. But I get no continuity to the junction of R52 & R53 nor to the junction of C48 & C49 not to the junction of C50 & C51. However there is continuity from the junction of R52 & R53 through to the junction of C50 & C51.
Could this be what's causing all the trouble?
If you look at the circuit just to the right of the main filter caps C46 and C47 you will see two "ground" symbols; the first implies mains ground/chassis, the second (triangle) implies amp signal common.
Quote from: jimmy74I get no continuity to the junction of R52 & R53 nor to the junction of C48 & C49 not to the junction of C50 & C51.
Well there should be, and yes this will cause the problems you are seeing, so you have to find out why the ground common doesn't carry through from the main filter caps to the regulators and beyond by tracing/inspection.
If this is a double-sided PCB (i.e. has copper traces on the top component side) then something like a regulator leg may need to be soldered on both top and bottom sides.
It isn't a double sided circuit so all that is possibly tracable is underneath. What exactly should I look for?
thanks
Quote from: jimmy74 on December 06, 2013, 02:33:20 PM
What exactly should I look for?
That circuit is very simple and follows the datasheet example, so you must check that all torn/cracked/missing tracks and pads are there and each 3886 leg is connected where it should.
If *one* connection is missing, it won't work.
I don't wish to dampen the enthusiasm here but I've recently spoken to a chap who works for a local Sight and Sound company who run quite a few gigs around these parts and they purchased several of those Db powered rigs and half of them blew up in the first 6 months. :-X
Hence they sold them off real fast. :grr :grr
My concern is small bridged chips claiming humungous wattage :lmao: :lmao: is a real worry and even if you are able to fix it it may well blow again. :'(
On the bright side *IF* the unit can't be fixed you can just make a cover panel and use it as passive speaker.
You have a big heat sink, PSU and likely some other bits to make a complete Amp rig.
The PSU is the most expensive part of building power amps.
I'll bet the Do-nut transformer is quite capable of driving a 50~100 watt Amp and the Filter caps will also save you money.
You can likely pickup a barebones Amp kit for $50~$80 au.
But meantime you are gaining experience by fault finding this unit and heaps of professional help makes life easier.
Hope it works out for You, :tu:
Phil.
Quote from: jimmy74What exactly should I look for?
There should be continuity from CONN11 to the join of C46 and C47, then to R52 and R53, then to C48 and C48, etc.
You say you measured NO continuity from R52, R53, C48 and C48, to ground.
You now have to find out
why, and restore it. Start at the join of R52 & R53 and trace back towards C46 and C47 until you find a broken track, missing jumper, whatever.
Ok I actually tracked from the junction of C46 & C47 to the next point joined by a jumper track(I think all jumper traces are on top of the board so it is a double sided board) and probably a cold solder point or faulty trace which I bypassed with a short piece of wire. Now I get continuity to pins 7 of all the chip amps, and to the ground points that were "left out" before, through to CONN11.
voltages on the regulators now are:
LM317
Pin 1 adj = 12.4v
Pin 2 out = 13.7v
Pin 3 in = 37.7
LM337
Pin 1 adj = -12.6v
Pin 2 in = -38.1v
Pin 3 out = -13.9v
looking better?
new voltage chart for the chip amps (not installed):
http://www.flickr.com/photos/73835524@N00/11291983513/in/set-72157638111984374 (http://www.flickr.com/photos/73835524@N00/11291983513/in/set-72157638111984374)
Quote from: jimmy74voltages on the regulators now are:
LM317
Pin 1 adj = 12.4v
Pin 2 out = 13.7v
Pin 3 in = 37.7
LM337
Pin 1 adj = -12.6v
Pin 2 in = -38.1v
Pin 3 out = -13.9v
looking better?
Not ideal perhaps, but +/-14v is quite satisfactory.
If the link isn't an actual wire then the holes at each end will be "plated-through" and one of them has given up - normally due to abuse of some sort. If there is one such then be aware that you may strike this again around the main chip amps.
Only the jumpers are done this way, all the other traces are on the underside of the board. Have you taken a look at the chip amp voltage chart?
Quote from: jimmy74Have you taken a look at the chip amp voltage chart?
I have, and I can't see anything that looks out of order there.
I'd suggest that you now try fitting one of your LM3886 chips in the treble amp position, clip your meter to its speaker output terminal (speakers disconnected), and give it a short burst of power via the limiting lamp (which should flash and then go dim).
If the voltage settles to zero (or within half a volt), that looks good. If the voltage goes anywhere else (most likely full +ve or -ve, or perhaps the chip shorts the two supply rails together) then I'd mark that chip as dubious, remove and place to one side, and try another.
If it goes well however I'd fit another chip in one of the other positions and repeat.
The aim here is twofold; to identify any of the power chips that may have been damaged, and to try and get three good ones in place.
If you get to this point you can try connecting the speakers and gently feeding a signal in and see what happens. With the previous wild preamp supply voltages it is quite possible there is still dead silicon to be found in the preamp section, but having good supply voltages at least is a good sign.
would it be wise to take the voltage readings of the opamps first? (BA4560's and BA6110)
As for the "treble amp" position, do you mean U5? And if so that would mean clipping the meter to J5 and J6 right?
Quote from: jimmy74would it be wise to take the voltage readings of the opamps first? (BA4560's and BA6110)
When it comes to electronics it's wise to measure (and write down) everything you can, and you can give the preamp a going over before tackling the output stages if you want.
Since the preamp runs on split (+/-15V) rails a simple test for op-amp health is that their outputs should all be somewhere close to ground for DC. Possible exceptions are U3A and U3B; but what you are looking for is that the outputs are not stuck at +ve or -ve rails. Since the preamp is AC coupled to the main amps it is possible for the pre to be damaged and not working, but be no threat to the main power output chips.
Yes, U5 appears to drive the tweeter; again, a healthy chip should bias its output to something very close to ground, zero volts, and stuck at + or - 40V is a bad sign. The meter check is to ensure that there is no (less than half a volt) DC voltage across either of the speakers.
Once you are quite sure that all three of the chip amp outputs (pin 3) are within half a volt of ground you can try reconnecting the speakers and driving the rig (
gently) with a signal from your MP3 player or whatever, and see what happens (still via the limiting lamp of course).
If all seems well, no nasty distortion, smoke or fireworks, then you can try using a higher powered lamp, and if everything is still okay apply full power and test. Note that while using the limiting lamp the amp will only operate correctly at low levels; if you try and crank it the lamp will light and the amp will distort.
But first you have to check out each of the chip amps as in my previous post.
sorry for the late reply, finally got down to getting the readings off the opamps, from U1 to U4 which are BA4560N's getting -13.8 off pin 4 and +13.7 off pin 8 so that looks normal. U6 BA6110 here's what I'm getting:
Pin1 = 0.5v
Pin2 = 0.5v
Pin3 = -12.7
Pin4 = -12.9
Pin5 = -14
Pin6 = 2.8v
Pin7 = 2.8v
Pin8 = 2.7v
Pin9 = 13.7v
Pins 6 & 7 are soldered together. Everything look normal here?
I can't see anything abnormal, so here's hoping.
The BA6110 is a rather unusual type of "op-amp" which is a current-controlled gain block, the gain being set by the amount of current flowing into the CNT or control input via R19. (the datasheet shows pin 4 as "no connection" so I don't know what is going on here, maybe a different package, however...)
The output is sensed for overdrive via U3b, and its output is used to reduce the gain of U6, making a form of automatic volume control, similar to a compressor. This is a desirable characteristic in a PA amp but not really what you want in a guitar amp.
Since there is nothing obviously wrong with the preamp you can proceed to sort out the power amp chips as outlined above.
maybe a silly question, but isn't pin 3 on the BA6110 supposed to be positive?
This data sheet shows pin 3 as an input.
http://pdf1.alldatasheet.com/datasheet-pdf/view/36051/ROHM/BA6110.html
Well I'm having a hard time trying to understand where exactly should I connect the meter clips for the output test, U5 in the schematic is connected directly to J2 and J6 but there's no continuity from pin 3 to any of the connector pins... another shorted jumper?
got it fixed it was a shorted jumper just like the other one!!
Anyways fitted in one of the amp chips in the U5 position, clipped the meter leads to the output pins for the tweeter, gave it a short burst through the limiter and the tester went above 2vDC, I changed the meter setting to 200v and the amp gave me around 31vDC... so it's a bummer?
thanks
Quote from: jimmy74shorted jumper
I think you mean "open".
Quote from: jimmy74the amp gave me around 31vDC
If that's output to ground, across the speaker, then yes it looks like it's boofed. Mark it as sus and try another (but do check the actual chip legs to make sure that -ve supply is actually getting to the chip).
Repeat until you get to one that has less than +/-0.5V across the speaker.
I checked the voltages with this amp chip soldered in, -ve voltage to pins 4 & 6 are -37 but on pin 8 I'm getting -3 instead of -13, could this be indication of a fried chip?
thanks
Is the output pin within half a volt of ground?
No the output pin is giving me around 31vDC.
I'm *quite* certain that some tracks or pads are either cracked open , missing, etc.
That circuit is quite simple, but if its pins are not connected to what they are supposed to, no LM3886 will work there, even the newest freshest one.
I suspect (heavily) that that PCB has been butchered beyond repair by now.
I would get/buy/make an LM3886 PCB, mount the chipamp there, bolt it to the heatsink "upside down" (no 2 solid bodies can occupy the same physical space, and the old PCB is still there) and connect proper +/-V rails, ground, in, out with short wires to the approppriate points.
I do that all the time, specially to repair amps with unobtainable chipamps (TDA1514 , uPC1188, etc.).
Build what I suggest on the bench, "outside " the amp, just getting power and ground from it, obviously bolted to a heatsink, and test it with music.
Once it works, "transplant" it inside.
Ok I fitted in another amp chip and this time it behaved properly, going to zero on pin 3, however I'm still getting -3v on pin 8.
After pulling the first amp chip, I remeasured the voltage on pin 8 and was getting -13v, so the -3v once the chip is fitted in must mean that the amp chip is pulling the negative voltage down or is this normal?
thanks
Fitted in another chip amp in the U8 position, tested the voltage on the output pin, 0 volts and pin 8 is -2.5v.. The limiter lamp lights up very dimly (it's 40watts), is this normal? Should I proceed to placing the last chip amp in the U7 position?
Is the -2.5v on pin 8 indication that the chip(s) need to be replaced? If the 0v on pin 3 means the output is correct, then should I proceed to fitting in the thrid and last amp chip in the U7 position?
Also where do I find the correct length chip amp mounting screw isolation washer for this sort of amp chip?
thanks
went ahead and fitted in the thrid and last amp chip, the current limiter lights up at first then goes down to a dim glow, pin 3 for all amp chips is 0 and pin 8 is -2.3v.... what next?
opinions?
thanks
After turning on and checking you still have 0V on pin 3 , connect a speaker first and drive it with music, repeat with the other, then with both.
Ok the only problem is that I can't attach one speaker at a time, the tweeter and speaker are both attched to the same 4 pin plug
That shouldn't be a problem to a Tech armed with nippers, pliers and a soldering gun ;)
ok I mounted the amp inside the speaker cab, tried it first with the tweeter/horn and it was hissing but the amp doesn't go in protection and volume makes the hissing get louder. I then tried with the speaker only and the same result only difference is that the noise isn't a hiss but a crackling sound with a continuous airplane noise in the background. Tried with both horn and speaker and still the amp didn't go in protection mode so noise apart I think we've got it on the right road.
what's next?
Merry Christmas to all and have a wonderful New Year!!
Quote from: jimmy74volume makes the hissing get louder.
Sounds like a bad case of snakes. ;)
More seriously, that's a fairly good sign that the power stages are now operating, but given the wild voltages previously applied to the preamp op-amps I wouldn't be surprised if one (or more) have died.
Feed a signal source such as an MP3 player in the front end, and lacking a CRO use a powered computer speaker to trace the signal forward from the input, and each op-amp output, until it vanishes to localise the problem.
is there anyone in the EU that sells the right sort of insulator bushings for the LM3886? I think the TO-220d type bushing should be correct but searching ebay the only seller is in China.
For odd shapes often the best is to buy a small piece of Silpad rubber sheet (warning, it's relatively expensive) *once* and cut small customm pieces as needed.
It's a good investment.
Other solution is to buy 2 big mica pada (for TO218/247 and larger) and use 2 side by side.
You'll have to punch your own bolt hole.
Thanks for the reply but I don't need the mica spacer, the original ones are still fine, I need that plastic but that separates the chip amp mounting screw from the base of the chip amp so that there's no connection between the heatsink and the base of the chip amp:
http://www.ebay.co.uk/itm/Insulation-Bushing-for-TO-220D-Transistor-Washer-x-50-/130579772765?pt=LH_DefaultDomain_0&hash=item1e6729355d (http://www.ebay.co.uk/itm/Insulation-Bushing-for-TO-220D-Transistor-Washer-x-50-/130579772765?pt=LH_DefaultDomain_0&hash=item1e6729355d)
these are the only ones I could find
Hi jimmy,,
Trash bins mate that is where you find all those hard to get bits. :dbtu:
Old TV sets/ stereo units/ dead computer supplies,, plus the hundreds of other electrical gizmos folks just throw out in this throw away world. All the better for us tinker types. <3)
Phil.
If you really can't find the right thing take a plain fiber washer and a short length of heat shrink, put the washer on the screw and follow it with the short length of heatshrink. But as phatt says, go for a scrounge in an old TV or amp. You shouldn't need to go to China, electronics suppliers here sell such washers/bushes, as well as nylon screws and nuts, and I'm sure you'll find someone closer, e.g.;
http://au.mouser.com/catalog/English/102/APAC/1771.pdf (http://au.mouser.com/catalog/English/102/APAC/1771.pdf)
Pulled apart some old burnt up PC power supplies I had lying around and sure enough there were some of those insulators... thanks for the tips!!
Quote from: jimmy74 on December 27, 2013, 03:11:20 PM
Pulled apart some old burnt up PC power supplies I had lying around and sure enough there were some of those insulators... thanks for the tips!!
Yo! That's the ticket. Scrounge. Every tinkerer needs a well stocked junk bin. :dbtu:
well after a very long delay waiting for he new preamp opamps, I swapped ou the BA6110 and one of he BA4560's and sure enough that got rid of the crackling noise. Still usin the current limiter I hooked up a guitar and everyting seemed to be working fine, no noise or problems so I mounted everything back up and playd through it for around 10 mins without the current limiter, eveytn seemed perfect, when all of the sudden it just went dead, vey low sound coming from the horn, it doen't go in protection mode though.. one of the amp chips dead?
thanks
Oh dear. Sorry to hear. :'(
Well you are just going to have to go for a dig again, but at least this time you have a much better idea of what you are looking at/for. It may be the chip amp, but it could be lots of things, broken track, dodgy solder joint...
Since the "protection" is an automatic level control that operates in the preamp and isn't coming on it suggests that this time the problem may be in the preamp ahead of the protection circuit ... fingers crossed.
here are the voltage readings I got:
http://www.flickr.com/photos/73835524@N00/12134847064/ (http://www.flickr.com/photos/73835524@N00/12134847064/)
the +ve and -ve 29.9 readings follow back to the rectifier bridge, and after its 21 and 22vAC
thanks
Well those voltages, particularly the pin 3's at zero, suggest that the three power amp chips are okay.
Quote from: jimmy74very low sound coming from the horn
You're only going to get signal content above 2.5kHz from this path, so I would expect it to sound pretty quiet from a guitar. This also suggests (along with the limiting LED not lighting) that the gain reduction/protection U6 is not kicking in, which leaves the path between there and the main amp input, U4A&B.
If you inject some sort of a signal to the join of R45 and C34 you should get some sort of output confirming the main amp is okay. If so look back to U4, if not you have a break or short after there before U8 (cracked track at U8?).
I still think you have a dry solder joint or cracked track somewhere, and if it's a crack it's a fair bet it will be very close to one of the solder joints (but may be well hidden).
HTH
I tried resoldering all the solder joints of the parts that I had changed out, redid the voltge tests but all the same. So I replaced U4 but nothing changed there either. I did notice that U6 is giving me -12.6v on pin 4 again. Wouldn't the lower 10v on the main power rail mean there's a problem in the power supply or somewhere there's something sucking up +ve and -ve 10vDC?
Pin 4 on U6 is the control input, and from my reading of the circuit will limit/disable the signal to the power amps when it goes +ve, and I would expect the red LED to light; -ve should be enable, green.
Quote from: jimmy74Wouldn't the lower 10v on the main power rail
Sorry, what? In the voltages you give on flickr the lower power rail is -28V. After the regulator U10 it should be about
-15V.
Have you tried to...
Quote from: Rolyinject some sort of a signal to the join of R45 and C34 you should get some sort of output confirming the main amp is okay.
?
sorry for the confusion, I forgot about the low power rail voltage being odd too and was considering only the high power rail. I'll try injecting a signal at that point today.
thanks
J.
I also took voltage readings off U3:
Pin 1= -11.7vDC
Pin 2= -12.5vDC
Pin 3= -12.6vDC
Pin 4= - 14vDC
Pin 5= 0
Pin 6= 1.28vDC
Pin 7= -12.6vDC
Pin 8= 13.6vDC
From your voltages I assume that the LED is green, and therefore U6 should be enabled.
yes the led is green, I found another dead jumper right at the junction R45 & C34, bypassed with a piece of wire but voltages are still the same so I'm just about to do the signal test and let you know the results.
thanks
j.
Well I was hoping in getting my portable cd player to inject some music into the amp though a jack to RCA cable but when I touch the junction point with the RCA tip I get a loud hum so I'm supposing the power amp is ok. I replaced U4 yesterday and redid all the solder points.
UPDATE: I plugged the guitar in and it works, I get nice loud sound, no noise, the current limiter bulb lights up stronger as I play harder or turn up the volume but there's still -2.3volts off pin 7 on the amp chips... what's going on?
Pin 7 is the ground pin.
What are you measuring -2.3V with respect to, i.e. where are you connecting the -ve probe of your meter?
So what do you think you did that brought it back to life?
Sorry I meant pin 8, measuring as usual to ground, -ve probe of the meter to the heatsink.
I suppose maybe after instaling the heatsink one or more of the solder pins on the amp chips may hve move and with the vibrations may have caused intermittent connections, and also that dead jumper may hve lso been part of the cause.
thanks
J.
K. :dbtu:
So should I just leave it like this or start tracking down what's eating up +/-ve 10 volts?
Very bottom right or cct is R57 and C54. These are the switch on anti-thump, and operate on the Mute like of the power amps. This will normally be pulled high at switch on because the cap is uncharged. As the cap charges through R the voltage tracks from +ve to -ve rials, but somewhere it gets to the Mute threshold voltage, and the rest is of no interest. So what is the Mute/Un-Mute Voltage.
Quote from: LM3886.pdf, p3
Pin 8 Open or at 0V, Mute: On
Current out of Pin 8 > 0.5 mA,
Mute: Off
The voltage is not stated since this is a current-operated switch; if you draw more than half a mil out of the Mute output, the chips un-mute. The 10k pulldown to to -15V, R57, 15 - 2.3 =12.7V, a bit over a mA which should be enough to un-Mute all three chips.
Sorry, but I'm back to "um what?" Specifically
what missing 10V are we talking about?
the shematic states +/- 40vdc on the main power rail and +/- 15vdc after the VR's. Also the tests I did over a month go gave me these results:
http://www.flickr.com/photos/73835524@N00/11291983513/in/photostream/ (http://www.flickr.com/photos/73835524@N00/11291983513/in/photostream/)
whereas now I'm getting these results:
http://www.flickr.com/photos/73835524@N00/12134847064/ (http://www.flickr.com/photos/73835524@N00/12134847064/)
there's around 10v difference on all readings
Your mains voltage dropped or you are using a different tap in your transformer or your meter battery is flat (no kidding).
Or you are using a lamp bulb limiter.
Please confirm which one is it.
Quote from: J M Faheylamp bulb limiter
Oh,
that 10 volts! :lmao:
Ok tried without the current limiter and the main 40v rail gives me 37v so that's ok but where I was getting -13v before, now it's stil -2.3 (pin 8 on the amp chips).
I tracked back the negative voltage to R57 which on one end is connected directly to the LM337 -15v supply and infact reads -13.4vDC. On the other end which tracks to pins 8 on all amp chips an to the negative side of C54 reads -2.3vDC. R57 is 10k and after a few seconds of steadily rising readings it reaches 9.91k.
You seem stuck on the -2.3V on pin 8. Looking at the datasheet this appears to be operating normally. More to the point is what this voltage does after switch-on, which I would expect to shoot to +15v (Muted) then fall rapidly to some valve below ground (un-muted).
Do you have a problem? Are the output amps Muted? If not, no problem.
Quote from: jimmy74 on January 28, 2014, 11:45:10 AM
I tracked back the negative voltage to R57 which on one end is connected directly to the LM337 -15v supply and infact reads -13.4vDC. On the other end which tracks to pins 8 on all amp chips an to the negative side of C54 reads -2.3vDC. R57 is 10k and after a few seconds of steadily rising readings it reaches 9.91k.
OK, so you have -13.4V on one end of a 10K resistor and -2.3V on the other.
What is this telling you?
(hint hint Ohm's Law ::) )