The pots for gain/volume were a little scratchy when adjusted but not bad - then 1 day - poof no sound!
I changed the input jack, no fix. I changed the volume pot and gain 1 - no change - but while I was holding the circuit board in my hands a radio station started coming through the speakers/headphones - my thumb was obviously bridging something on the circuit board - but it was over the volume and gain pot area so this leads me to believe that the problem is still somewhere between the input jack and its entry into the circuit - any ideas?
When I turn the pots the sound is getting from the pots to the headphone jack (speaker disconnected as electronics are out of cabinet) but still nothing from input to pots as far as I can tell.
So essentially you can hear the speaker respond to your thumb touching the volume and gain pots. So there is amplified signal at the output but something before that location on the circuit board is not right. Can you take some close ups of that input jack area and the traces on the board that lead away from that part. Want to see top and bottom of the board to see if there are tl072 or 4558 IC or transistors used on the first stage of amplification from the input jack. No way to get this schematic as it is not online anywhere... Do you know how to trace signals? This link is in reference to tracing signals on effect pedals but will work as well in relation to your amp. From what I gather is that there is a 4558 IC right after the input jack and we need you to provide some form of reference.
http://www.diystompboxes.com/wiki/index.php?title=Debugging
Thanks for the help, I will try to get some photos this weekend and upload them. When I contacted the orange website I got this response from a dealer.
(I've worked on a lot of these and about the only two things that go out on a CR10 is a pot or the opamp in the U2 position - response from orange dealer when I posted on orange site)
I have no idea on wiring myself and circuit boards, I do fine with soldering and guitars electronics though and I redid the pots and input jack so I am willing to learn.
Sorry it took so long - any help?
Well okay I see the IC chip, looks like a JRC4558. So, I will first tell you that I don't like the looks of the solder joints on the input jack and have attached a pic to show. I am not sure but that joint looks like you should re-flow the solder a bit better, just for good measure. Also, those tabs on the pots need to be pinch off with some needle nose pliers. We can all help out on this but have you made any head way on understanding how to trace signals? Please ask questions as you go and we will help. Look at the pin out for the JRC4558 and realize we need to trace signal at some of those point. We want to see or hear signal at pins 1-3 and 5-7, especially pins 1 & 7(output pins). So start by injecting signal from an mp3 player on medium to low volume and then we need to trace that signal at those pins first. Please inspect soldering and be careful with those new pots, clip off the tabs. Good luck!
That solder joint was a last ditch effort to see if that was the problem - I found a site that said to connect the pins on that side of the jack. No problem removing that - the tabs either, just wanted to get it working before I messed with little things like that.
I will work on it over the next few days, thanks for the input so far, it helps.
To save some time, inject some noise in that preamp.
1) you have 2 amplifying "blocks" packed inside that 8 pin chip.
Each pin has some specific function.
To know how to look at it since it's symmetrical, on the end where pins 1 and 8 are there's either a notch (as shown) or a small hole in the plastic casing close to pin 1.
Some Korean chips use a printed white band to show that end.
The drawing shows it from above and as shown pin 1 is top left and you count counterclockwise , so pin 8 ends up being on the same end (but across the chip body).
2) Pins 3 and 5 are usually sensitive inputs, so put all pots on 5 , or halfway and with the tip of a small screwdriver touch either pin.
It should hum or make some noise, probably also a "tick" or a "thump" , plus "bzzzzz" or "hummmmmm" through the amp speaker.
It will be noisier if you actually touch the screwdriver metal shaft with your finger.
And if you touch the metallic chassis with the other hand, hum will be lower because now you are grounded.
After you get sound, move all pots one by one (preferrably using the plastic knobs so you do not touch metal with that hand) and take note of which have some effect, such as "treble works but gain does not" or whatever.
All this on pin 3, then repeat on pin 5.
I'm trying to find the input where all pots do something, because that's the input where the input jack must be connected. 8)
Quote from: greybox on September 23, 2014, 05:08:41 PM...I found a site that said to connect the pins on that side of the jack....
Just because I can't see that well in the pic and words can get confusing on forums. Are all 3 legs of that input jack connected together?
The piece of wire connecting those 3 pins on the jack must be removed. The way it is wired all jack contacts are grounded and it can not work.
Also, the pot you replaced (3rd from jack), it looks like one of the legs is bent over and the solder may be touching the ground trace. You need to make sure it is only touching the trace it connects to.
Finally had time to check all of these - all pins EXCEPT 1 make tick, thump or buzz some louder than other but all are present. (and i did remove the bridge across the input jack legs first)
Then maybe we have a dead chip or we are missing either or both the +/-15V lines.
Pin 4 is -15 , Pin 8 is +15, none should sound at all just by touching them with the tip of a screwdriver.
Or you fully lost ground between preamp and power amp or supply.
Please measure DC voltage at all 8 pins and post it here.
Use the 20V DC scale, connect black probe to chassis ground and measure with the red one.
All of the pins except 1 made noise - so do I give a new chip a try? I don't have a voltage tester and am starting to question whether its better to keep working on it or find a working amp cheap on craigslist and put the electronics in the orange cab with the orange speaker...I don't mind working on it, just trying to decide if this is going to become a(very low end) money pit....
You ask without answering first
QuotePlease measure DC voltage at all 8 pins and post it here.
No further dialogue possible without.
As of "money pit", an RC4558 costs less than a buck.
You might have to buy a new jack, another buck or two at most.
How much will a craigslist amp cost?
What if the seller "forgot" to tell you that pots are scratchy or that you have to insert a toothpick in the jack together with the plug to make it work or ... or ... or .... ?
Yours looks in working order, just with a small repairable defect.
Now if a neighbour sells you a perfectly working one for $10 .... yes, in that case I'd grab it.
I might have spoken too soon only in the fact that if the legs are all making noises than how big of a problem am I looking at (Yours looks in working order, just with a small repairable defect.) that's all I was hoping for - thanks. I will check into getting a voltage meter soon.
okay - tested chip starting top left and going counter clockwise (touching high on pin next to chip body)
pin1 = .2
pin2 = 0
pin3 = 0
pin4 = -17.3
pin5 = -17.2
pin6 = 0
pin7 = -16.1
pin8 = 16.3
When you measured did any of the voltages produce a negative voltage?
Perhaps pin 7 is stuck to the pin 8's rail? Also pin5 is stuck to pin 4's voltage rail? I am not sure if that could be the case here or not, maybe. Pin 5 & 7 should have millivolt readings and what we are seeing is similar to the voltages on pin4 & 8.
Disconnect the speaker and measure to check if there is any significant DC voltage on the output of the amp. Place black meter on the negative speaker terminal (or ground) and put the red meter on the positive speaker terminal plug. Do this all with the speaker disconnected.
Modified my post to show negatives in previous post. speakers = no measurements (randomly .1 - usually 0 though)
This is harder to navigate without a schematic... Still I would remove that 4558 IC chip and then power it up to measure where the pins were connected. It is possible that the chip is bad and it would be good to see the voltage readings without the chip in place. For the price of a 4558 chip it is worth just installing a new one to see if it fixes the problem.
That RC4558 looks very dead.
There can be no (or a couple mV ... single digit) between pins 6 and 5 .
Carefully desolder all 8 pins using a good solder sucker, then pull it while cold away from the PCB, it should come out easily.
Do not wiggle parts legs whilke solder is molten, pad to base material is weakest at that temperature and it's very easy to pull that pad with the slightest movement.
If possible, put an IC socket there so if you have to replace that IC later the board does not suffer.
Measure all 8 pins again without the IC present, as suggested above :)
Although I basically suspect the IC itsel, we *might* have a cracked trace .
+/-15V are reaching that IC normally.
Slightly high, but it might be because of lack of consumption.
I lucked out and actually got the replacement chips today, I ordered them just in case. I will work on it tomorrow and fingers crossed have an orange amp again
:dbtu:
Just work slow and careful, pamper the PCB, clean old solder well before pulling the IC out.
Just to make sure,measure voltages on all 8 pads without IC to rule out that some weird voltage is coming from somewhere else (besides the +/- 15V on pins 8 and 4, that is).
Oh, and mark which way pin 1 (or the marking notch) goes.
Unfortunately it fits the wrong way too.
WOOHOOO!!!!!! Fixed - new chip in and sounds fantastic (and I upgraded the chip to a TL072)! and because I started troubleshooting with the pots and input jack it has no scratchiness left either!
and just as important I have accomplished my first ever amp fix! (changed the tubes and speaker on my VOX before but other than that nothing else)
Thanks for the help guys!
Congrats on the amp fix!! Isn't a great feeling when you repair something to working condition again? I get a high feeling for about an hour and then I am bummed cuz I don't have to figure the problem any more. Then it is on to the pursuit of more broken amps to fix!!
Amps are all working now, did a pickup swap and strat mod yesterday...now I just have some playing left...what fun is that...
Quoteam starting to question whether its better to keep working on it or find a working amp cheap on craigslist
Quotejust trying to decide if this is going to become a money pit....
Ahem !!!! :trouble
The Forum Complaints guy is going to have a few words with you .... as soon as he's finished dealing with another ....
complainer ....
(http://kevanna.net/wp-content/uploads/cat-o-nine-tails.jpg)
:lmao:
I know...it was more just wondering how far down the path I was going to have to go, $5 here, $8 here...I only had $50 into the amp to start with....
Don't worry :)
As you see, it turned out quite cheap.
The price of servicing is 1% parts and 99% finding which the bad one is.
And (so far) we aren't charging for the detective work ;)
Quote from: J M Fahey on October 09, 2014, 01:32:51 AM
The price of servicing is 1% parts and 99% finding which the bad one is.
And (so far) we aren't charging for the detective work ;)
...although we do often expect a certain amount of
effort. 8|