I have a HH MA150 PA 5 Input Mixer Amp with 2 HH Pro 100 Speakers that I use indoors. It is in near mint condition because it has never been abused.
Just before Christmas I was using it to play some backing tracks, I left it switched on (with nothing playing through it) left the room for 5 minutes when I returned it was making a loud humming noise! I checked
all the connections etc. and they were all fine. 30 years ago it died and I had it repaired, I was told it was the output resistors. I am more electronic savvy now having done some work on valve amps so I can use a
meter/solder read schematics etc. but not much experience on SS.
I checked the 4 resistors that were replaced last time and 3 were burnt and way out of spec. So I replaced all 4. The amp switches on, everything lights up, nothing smoking, its cured the humming, but no sound at all?
Well, it can be repaired :)
But now you do a little homework 8|
1) google and post or link the HH MA150 schematic, at least its power amp
2) tell us *which* "4 resistors" you replaced.
3) read the lamp bulb limiter thread here in this Forum and build one, you'll need it.
Hi JM Fahey,
On August 15th 2014 a member on this site by the name of Mike H had a similar problem and put a schematic on his post by the name of, HH MA150 Help Please.
I'm sorry but I don't know how to do a link.
The 4 Resistors I replaced were, R26, R27, R30, R31. Upon double checking R30 and R31 are in spec but were a bit black, this is why I changed them all.
I removed and checked the 2 internal fuses and they are OK.
I'll build a light bulb limiter.
Ok, I found him searching his name and posts.
For the next time, in such a case you simply open the page you ant to show us, copy its address from the top address bar and paste it here, so clicking the"link" sends us straight there.
In this case:
http://www.ssguitar.com/index.php?topic=3550.0
the circuit is:
(http://www.ssguitar.com/index.php?action=dlattach;topic=3550.0;attach=4825)
Now to some diagnostics:
* blown R26-R27 tells me that VERY probably power transistors Q1 and Q2 are blown, probably blown open or you would be blowing mains fuses by now
* toasted R30 tells me the amp oscillated, big time, which is an excellent way to cook the output transistors.
* toasted R31 tells me that the amp was driven into a short or a very low impedance (did they hook half a dozen cabinets to that poor amp?) for an appreciable time, and didn't smell the smoke rising from it.
you'll have to check Q1, Q2 , Q6 and Q7 at least for shorts.
Hi,
Update on amp history, the amp repair from 30 years ago was because I lent it a Social Club when they had an emergency, I don't know what speakers they hooked it to, but that's what
blew the resistors the first time. It had been running perfect ever since.
I am the only one to use it since and have only used it with the proper HH Pro 100 Speakers,
so no mismatch with impedance. It has never been driven hard or abused.
I tested the transistors Q1, Q2, Q6 and Q7..... Q2 and Q6 are faulty.
Ok, not the most orthodox way, but to save time I'd replace Q1 - Q2 - Q6 - Q7, even if a couple does not show shorts (as said before, I suspect some might have failed *open* ) , of course desoldering carefully, pampering the PCB, would also replace R25/26/27/28 , plug the amp into a light bulb limiter and turn it on.
No speaker or any load connected, also no input signal and all controls on 0 .
*Maybe* that's all there is, speaker out rail stays within 200mV of ground and later connecting a speaker and applying some signal lets us hear some Music :)
If not, we keep troubleshooting.
I guess power transistors are TO3 metallic, in that case a pair MJ15024 would be fine; also MJE15030/31 would be good as drivers.
Just doublecheck pinout on TO220 drivers, to make certain they match originals.
I'd be concerned that this issue has happened before so something is not right.
Am I right in thinking that the current limit setup may not be working?
Just think'in out loud , Phil.
Agree, also think very possible that those current clamps are shorted, thus always clamping.
But I want to keep this step by step troubleshooting so for now I'd just be happy to restore low DC at the output conditions plus no fuse blowing.
Later, we'll feed some signal and your prediction may very well be found.
Hi,
You say replace R25/26/27/28 in my earlier post I did say that I have replaced
R26/27.
On the schematic there are two R25's, one on the Driver PCB and one on the
Pre Amp PCB. I assume you mean the one on the Driver PCB?
I haven't had time to make a light bulb limiter yet. I'm going to be a bit busy
the next 2/3 day's with other things, so progress might be a bit slow!
Phil,
Thank you for you concern, but since the last repair the Amp has worked fine for the last 30 years, which I think isn't too bad!
Regards,
Baz.
Quote from: bazmusicman on January 02, 2016, 06:23:23 PM
Hi,
You say replace R25/26/27/28 in my earlier post I did say that I have replaced
R26/27.
I give you the full recipe.
If you already did some of it, fine.
Not forgetting that if the transistors are shorted emitter ballast resistors might have blown again.
QuoteOn the schematic there are two R25's, one on the Driver PCB and one on the
Pre Amp PCB. I assume you mean the one on the Driver PCB?
Today I'm worried about a dead power amp, didn't even *look* at the preamp.
QuoteI haven't had time to make a light bulb limiter yet. I'm going to be a bit busy
the next 2/3 day's with other things, so progress might be a bit slow!
Take your time ;)
QuotePhil,
Thank you for you concern, but since the last repair the Amp has worked fine for the last 30 years, which I think isn't too bad!
Things can work for ages until they die or fail ;)
Thank you both for your help, it really is appreciated.
I will recheck the resistors that I replaced, and test R25 (on both boards!) and R28.
I checked all the said resistors and they are fine. I have removed the 4 transistors, just need to obtain replacements and fit.
I have a friend bringing a Variac to me later in the week so once the amp is back together maybe we'll get it back up to speed hopefully without anymore problems.
I'll keep you informed on progress.
Well I'm having a problem obtaining replacement transistors!
I know what you are thinking - you can get transistors most anywhere - I can get Q1 (tip 29c)
and Q6 (tip 47) no problem, but Q2 and Q7 are both SM2177 which I am having trouble finding a replacement/alternative. I have found that Semelab PLC appear to be the makers stating its BJT PNP 200V 30W. This info may be right / maybe wrong but anyway they are discontinued!
I have tried several 'cross reference' sites but I can't seem to find an alternative. Any help would be appreciated. I don't want fit the wrong thing and cause more damage.
Unless I'm sadly mistaken just find a 200V 30W rated BJT (or above) and it will work, though check the pin out. No matter what you do, run it with limiting lamp or variarc until you know it's stable.
In my DIY experience, it needs to be able to run at full power into a load before you know it's stable. If something gets insane hot (the instant burnt finger bias test) then it won't last long. Sure if you never turn it up full pelt then it may well last 30years in tender hands but one day it will fail again,,,,, if it was my amplifier *THAT* would bug the hell out of me. :trouble :grr
My recent adventure into design and build of a power amplifier took me quite a while to perfect. My final test, ran for 8 hours into a 4 Ohm load and my temperature probe could not get past 35 Deg C at any point in the circuit.
Only the load box got hotter, which is what you want.
You might find some very helpful info and tips here;
http://sound.westhost.com/index2.html
click on *Articles*
Power amp circuits here;
http://sound.westhost.com/projects-0.htm#pwr
Phil.
Hi Phil,
Thank you for your help and those links, that is some very interesting reading and tips.
Regards,
Baz.
Houston, we have a problem :grr
The same transistor designation was repeated twice in the same schematic and PCB :grr :trouble
Q1 and Q2 are used at the beginning of the power amp and also as power transistor designations.
To differentiate them I'll use Q1 and Q1(p) (power) , same with Q2 and Q2(p) so please follow the same system.
Modern equivalents first best, then acceptable if best is impossible.
Q1: TIP29C = available
Q2: SM2177 = MJE15031 or TIP32C
Q3: BC204 = available
Q4: BC207 = available
Q5: BC204 = available
Q6: TIP47 = available but MJE15030 is better
Q7: SM2177 = MJE15031 or TIP32C
Q1(p)/Q2(p) TO3 case: HH9080 = MJ15024 BUY ONLY FROM AN ON DISTRIBUTOR OR MOUSER OR (maybe) FARNELL .
When you see a house number like SM2177, look at the circuit. Q6 is a TIP47, which means that Q7 will just be its PNP complement.
I also think you might as well use more modern transistors. TIP47 could be replaced with MJE15032, while the PNP would fit a MJE15033. Your power amp has 120v of power supply, so the transistors need to be at least 150v types, I chose 250v types to be safe.
For the SM2177 you can use a PNP complement to the Tip47.
Or some use MJE15033 in the HH with no problems (and you can use MJE15032 for the Tip47).
Edit: sorry Enzo, we were thinking the same thing at the same time. :)
JM Fahey,
Thank you for beating me up, I deserve it!
I'm sorry if I have driven you to 'tear your hair out' with frustration but I did say I was a little green working with Solid State. You have helped me tremendously for which I am very grateful.
Now you have pointed me in the right direction I can move along. Thank you once again.
Also a big thank you to Enzo and g1 for their help.
Best regard,
Baz.
Latest update.
I made a 'light bulb limiter' fitted the new transistors, used a hundred watt bulb switched on and the bulb flashed and went too dull to see any glow, but the amp was on. I switched everything off and fitted a 40 watt bulb, switched everything back on, the bulb flashed and went to a very dim red - you can just see it in a very dark room - at least the Amp wasn't cooking - so I disconnected the limiter and tried the amp, but still no sound.
I took a couple of measurements from the Driver PSB that I saw on the other thread that I thought may be relevant.
+C = 53.4v.} these two I believe are in spec?
- E = 53.3v.} " " " " "
O = minus 51.0v.} ( I know that this one is way too high) should be about 200ma?
Any help with the next step would be greatly appreciated.
Regards,
Baz.
I think you mean 200mv - millivolts not milliamps. But yes, 200 of them is a reasonable maximum. You have 50v there, which means the whole thing is slammed over to the -50 rail. If you had a speaker there the thing would blow a fuse and the speaker burn out. No speaker until we have the output near zero.
The whole power amp is one big loop, so lets look at the 741 op amp IC. Pins 4 and 7 are the power supply pins, +15 on 7 and -15 on 4. Are they there? Note that for each 15v supply, there is a zener diode and a dropping resistor from 50v. If one voltage is missing, look at those.
Output of the 741 is pin 6, what voltage is there? That is what tells the output where to be. If that is over to one side, so will be the output. See D1 in the middle? What voltage is sitting on its ends? That should be roughly the voltage at the bases of the outputs, they follow it.
Hi Enzo,
Yes I did mean 200mv, not ma. I did connect the speakers when I tried the amp but the speakers still work and no fuses blown! Before that I noticed
Resistor R13 was very burnt, but it still measured 1K! Neadless to say I replaced it anyway.
With your suggestion's this is what I found.
Pin 4 minus 15.03v
Pin 7 minus 0.68v
Pin 6 minus 1.15v
D1 minus 52.2v anode, 52.8. cathode
ZD1 minus 0.69v
ZD2 minus 15.10v anode end only? would this be reversed biased?
These measurements were taken with the light bulb limiter in circuit.
Regards,
Baz.
So you are missing +15v. Go find it. You have two zeners. Note one has its cathode to ground the other has its anode to ground. Zeners work by applying a reverse voltage to them, then their reverse voltage "breaks down" in a designed way to leave a steady voltage across the part.
Without me looking at the schematic at the moment, either your zener diode is shorted, or perhaps the resistor from the higher voltage source is open, R7. If R7 gets hot, then ZD1 or the IC are likely shorted. If R7 stays cold, it may be open. However also check the upper end of R7 to make sure the +50 has reached it.
Have we verified that +50 is coming from the power supply and getting to the Q6, Q3, R7, etc.
Hi Enzo,
Resistor R7 is open, I have a boxful of resistors
but not a 3K3!
I have + 53.2v power feed to Q6, Q3, and to R7. I will replace the faulty R7 and take some more readings and let you know how I get on.
Regards,
Baz.
You got a 3.9k? 3.6k? Just get close, the resistor limits current, the voltage is established by the zener. Or do you have two 6.8k? Put two in parallel for 3.4k, certainly close enough.
No I don't have anything near or I would have used it. the nearest I have is 4.6k.
That's a good idea with two 6.8k in parallel, but I have some 3.3k's coming tomorrow.
Thank you for your help Enzo, I really appreciate it.
I fitted the resistor and remeasured:
Pin 4 minus 14.9v
pin 7 plus 14.5v
pin 6 plus 00.6v
ZD1 plus 14.6v
ZD2 minus 15.0v
speaker out 02.2mv
As the speaker out level is now right I tried it. The amp now works but very low on power and distorts. Is there something I've missed, Any ideas please?
Regards,
Baz.
Well, maybe not something you missed so much as something you haven't got to yet. You needed to get your power supply right before anything else mattered. Now that we have that, we continue on to find out what else the amp might need.
Now start checking out the amp. Plug the guitar into the AUX IN or SLAVE LINK jacks. Does it sound OK? That is the power amp input, so you are testing the power amp alone.
You can test the preamps too. Set up some other amp, with a guitar cord to that amp's input. Now plug that cord into the SLAVE jack. Does that preamp sound OK coming out the other amp? Now connect the other amp to the ECHO SEND instead. Turn on the FX switch on the channel ins, now how does that ECHO send sound? All input channels sound alike? Or just one or two sound bad?
Remember how that fouled up +/-15v situation made the power amp not work? Well the preamp has similar supplies. Look just left of the SLAVE jack, see the +/-15v supplies there? From the V+ and V- supplies there are 1k 3w resistors dropping down to 15v zeners. So are both 15v supplies present? Note these are totally separate from the ones in the power amp. And do you have good 15v supplies right at the ICs on the preamp?
We need to determine which section of the amp has the problem, THEN we can think about what to do about it.
I plugged the guitar into the AUX IN and SLAVE jacks, both sound fine.
I set up another amp as advised to test the preamp, slave jack fine, the echo send is fine and the same on all input channels. The two 1K3w R24/R25 resistors both measure fine.
R15 should be 3K3 but is 1K70? also R17 should be 3K9 but is 1K53? would this cause the low output/distortion?
A couple of others are a little out of speck.
Measured supplies to preamp;
supply 75 minus 14.9v
supply 76 plus 14.8v
Z1 plus 14.8v
Z2 minus 14.9v
IC3
pin 4 minus 14.75v
pin 7 plus 14.79v
pin 6 plus 00.10v
IC4
pin 4 minus 14.95v
pin 7 plus 14.81v
pin 6 0.00v
Regards,
Baz.
1k7 you measure for R15? Likely just parallel circuit paths lowering the readings. Look at R17 3k9. I bet that 1k5 reading changes if you turn the presence control up and down. Look at the schematic. In paralle with R17 is the path through R18, R19, and the presence control. That path adds up to something 4k4 to 8k9 depending on the control, and those parallel 3k9 cuts the total roughly in half, as you measured.
You have good 15v supplies at the ICs, all that looks fine.
If playing into the slave jack sounds fine out the speaker, and the preamp out the slave jack sounds OK elsewhere, I am hard pressed to think why it wouldn't sound fine going straight through.
Well I tried it 'straight through' and it was back to normal; full volume, no distortion, brilliant!
I put the bottom panel back on the amp and sat it were it always sits, turned it on and........
that's right, low volume and distortion!!!
back on the bench, remove bottom panel, preamp readings fine but still low volume /distortion.
Perhaps I need to check the capacitors on the preamp and power amp?
it sounds more like a connection to me, bad caps don't come and go.
If the preamp works and the power amp works, it only makes sense that straight through works. So go back and do the isolate thing again. Play through the input jack, and connect preamp out to some other amp as before, but also leave the amp speakers running. Now if the preamp sounds OK through another amp, does the speaker still sound OK? Maybe the bottom panel is touching something, or one of the screws. Try it with and without the panel.
The schematic doesn't show a cutout, but just for science, when it sounds crappy, plug a cord from preamp out right back to slave amp jack. Does that restore the sound?
The first thing I thought of was a bad connection. I tried moving the wires with a plastic chopstick without success.
I did also try it without the bottom panel, and looked to see if it was touching anything.
I'll try your suggestions and keep looking, I've got a feeling that success is just around the corner!!
My money is on the hidden switch inside the send return or Aux/link sockets (comes under many names but all do the same) It is by far the most common failure point and often intermittent so,, As ENZO mentions establish that Switch is making proper contact by jumping with a cable which bypasses the switch completely. If all runs fine then two options,,,, replace switching socket or if you are like me,, 8) just leave a short cable permanently plugged in,, I'm too lazy to replace the socket. ;)
Phil.
Thank you Enzo and Phil for your help and suggestions, I've tried them and although I get sound with them I also get sound using the amp normally through the inputs. As I said the amp works, but it has a very nasal like sound (read awful) and no volume, turning it up almost full you couldn't blow a candle out, and still be able to talk to someone in a 10' x 12' room without shouting.
I have gone through the cable joint's/wires anything I can see that might be loose or a poor connection. The main 'on switch' that lights when on, has a very faint flicker, could this be a sign of poor current flow?
As all the channels work/sound the same, I'm thinking its something on the main flow/output that is choking the signal strength? maybe I'll have to work from the output backwards?
Any other suggestions/idea's would be greatly appreciated.
I've got a feeling that success is NOT just around the corner!!
I don't follow you.
You said that it worked perfectly on the bench , then mounted it in the case and it lost tons of volume.
What is the situation
today?
What if you put it back on the bench as when it worked earlier?
We are not there, don't see what are you are actually doing.
Hard to
QuoteAny other suggestions/idea's would be greatly appreciated.
without a clear input.
If it works on the bench but not when bolted together, only a couple things come to mind. One is that perhaps tightening down the bolts flexes the chassis in some fashion or more crudely, maybe a bolt comes through the hole and touches something. The other is that maybe a component or a wire sticks up a bit too far, and bolting it together pushes down on that or pushes two things together.
But those arguments only apply if it CONSISTENTLY works open on the bench, but not closed up.
Sorry J M Fahey and Enzo, I apologize for being a bit vague, What I'm trying to say is that I put it back on the bench and it didn't matter what I tried, I couldn't get it to work properly again at all. It only worked properly that once. As I said it does work but its gutless.
I have checked for bad wiring/contacts, wires being squashed, screws touching anything etc. I even re-soldered a couple of joints that may have been dry. I'll recheck everything again.
Thank you both for your kind help,
Regards,
Baz.
The essence of troubleshooting is to isolate the problem.
Apply a signal to the input, then use a scope or a signal tracer and look stage by stage along the signal path, and see where it goes haywire.
Thank you Enzo, yes I agree, to troubleshoot you have to isolate the problem. This is what I have been trying to do.
I have a friend with a scope but he isn't local to me. I'll have to wait until he can come over.
Thank you all again for all your help.
Do you have another working amp? Use it as a signal tracer. Make up a cable to plug into it, and on the free end put a probe, a straight wire even. We want to add a series cap of some sort to block any DC the circuit might hold. Now we probe any point in the circuit and listen to what is there. Sort of an audio scope, if you will.
Yes Enzo I do have some other working amps.
I'm intrigued by the signal tracer idea, I've never heard of that. Could you please enlarge on how to make one?
I assume that I use a normal guitar lead with jack plug one end and a piece of wire the other end, but not sure where/how to connect the cap and probe?
Yes it's that simple :))) A cap on the end of a guitar cord. :dbtu:
On the rare occasion you may need a ground clip for a common path return but as most Guit amps are grounded chassis then the power cords Earth wire make the loop.
As you have established that both the preamp and powr amp work then the weak link is in the interconnections which is almost certainly in those 2 sockets and if they are enclosed plastic types then they are suspect to failure.
Although the schematic shows a hard link to both *Slave link and Aux out* it may not be wired as per schematic. the internal contacts may have broken *inside* the socket. I know the plastic types are a nightmare and at the age of the unit it maybe failing.
Maybe bypass those connections and hard wire the preamp out back to Pwr amp input to be sure?
I have an old Ross 16 Ch mixer with more than half of the 32 plastic sockets broken now the internal contacts no longer switch,, the threaded shoulder has broken on most of them.
Phil.
Yes, I have suspected all along that the two jacks are not wired as drawn, but have the slave jack as a cutout.
I have to suggest always using a ground wire from the work amp to the tracer amp, they may be grounded together through the mains cord, and that may be good enough for voltage readings, but the potential for ground loops that way is large, and often as not, when we are listening to the tracer, we don't want any added hum we can avoid.
The signal tracer used to be an actual piece of equipment on the bench. Nowdays we just make one up. But 50 years ago, no shop lacked one.
Like phatt said, simple as a cap on th end of a shielded wire fron the tracer amp input. Essentially using your own amp, the signal tracer is little more than a special cord. Official ones have an actual probe on the end, but many times I spun the cap off a gitar cord and used a clip wire and cap for the purpose. "Probe simply means something with a live tip you can touch to circuit points. Use the cap itself as a probe, watch your fingers and don't touch its wires.
The tracer lets you touch the tracer amp to any point in the circuit and listen to what is going on there. With the DC blocking cap, I can even listen to ripple on the power supplies. Cap value is not critical, I use 0.047uf/630v because I have tons of them. Just make sure the voltage rating is at least the highest voltage you might touch.