GGG TS-808 mysteriously stopped working. Any ideas?

[AppleScrappler]

My friend recently completed his first build (let us all pause and welcome a new pedal building geek into the world!).  It's a GGG ts-808 direct from the site built to standard specs with no mods (yet).  It worked on his first attempt and performed wonderfully for a week without any issues - that is - until now.  He was jamming with it one night and then went to use it a day later and it simply didn't work.  LED lights up when active, works fine when bypassed, but zero sound when the pedal is activated.  I'm not new to pedal building or debugging - I've spent many a weary hour trying to figure out why one of my builds didn't work only to realize I wired the input jack to ground or something stupid like that    so I was ready to help him and knew most of the issues it could have been right away because I've built this exact pedal several times before and have had to debug it.  I charged in confident that it would be a simple matter of a loose wire or accidental grounding or something along those lines.  That was several days ago.

I disassembled the pedal and took the guts out of the enclosure and plugged it into my guitar and amp and 9v power supply to test it.  No sound when active - as expected. I checked the voltages of the transistors and the IC and they check out perfectly (even though i ended up replacing all of them later on to see if they were the issue). I re-soldered every joint.  I checked (and eventually replaced) every relevant wire.  I experimented with hardwiring every pot and the the clipping switch in case they were mechanically failing.  I double checked that all the wiring was correct and confirmed that all the components were placed properly.  I checked the traces (visually) under the mask to see if any were cut.  I even replaced a suspect resistor that looked funny.  I've checked a dozen times for solder bridges or anything accidentally touching something it shouldn't.  I've done other things I've probably forgotten to mention, but alas nothing has even hinted at what the issue might be. 

I don't have the means to do an audio probe at this time.  The real mystery to me here isn't that the pedal isn't working... it's that it WAS working beautifully and simply stopped working.  To me that indicated a simple mechanical issue like a loose wire or bad solder joint and that the components are probably not to blame.  But now I'm beginning suspect there is something wrong somewhere I'm not experienced enough to visualize.  Although I know a bit about electricity and how these circuits work and have built dozens of pedals I'm still an amateur compared to many of the posters on this forum (who have saved me many times from throwing out my soldering iron!).  I'm just looking for any advice that can be given, I've scanned other debug posts but found nothing helpful.  Are there any specific components I should try replacing that may have failed?  Is there a common failing in the ts-808 I'm not aware of that could be causing this?

Remember, there is no sound coming through at all when the pedal is active.  Not even a hum.  And that doesn't change when I play with the pots, change the clipping switch, or even jiggle the guts around.  But the true bypass works so i know the jacks haven't failed me and at least a couple of wires are working 

I have all the necessary parts to replace anything on the board but I'm trying to avoid simply building a whole new pedal.  Any thoughts are welcome!  Thanks

[PRR]

Failed switch? Makes contact on the bypass side, not on the effect side?

Wire board in and out direct to their jacks, not via switch, see if that works.

[AppleScrappler]

Failed switch? Makes contact on the bypass side, not on the effect side?

Wire board in and out direct to their jacks, not via switch, see if that works.

Thanks for the response Paul.  I tried that and nothing has changed.  The mystery thickens...


I'm breaking out the sledge hammer next, but that only solves emotional distress issues... and only temporarily 

[Schappy]

If you use the improved audio probed described in the FAQ section it will save you many hours and many headaches. You may even be able to secure the parts at radio shack. Unless you are really lucky this is the only way to debug.

[AppleScrappler]

ok I'll give the audio probe a try asap (may be a few days) and give an update on whether I find the solution or not.   Any other suggestions in the meantime would be very welcome!

[Paul Marossy]

Audio probe it. I have been able to fix broken effects without even having a schematic by using an audio probe and common sense.

BTW, did you check the Vref supply? If that is bad, then it could result in it doing nothing. It won't pass any sound. Been there, done that.

[Schappy]

Read the debug thread as well. I have little knowledge of electronic theory at this point but the audio probe has been a savior.


Make sure all you voltages are right then start at the input with your probe. It has saved me tons of hours.

[petemoore]

Make sure all you voltages are right then start at the input with your probe. It has saved me tons of hours.
  Make sure all you voltages are right
  pretty much guarantees the amp is working, but says little or nothing about the signal path...great debug shortener [if there's a voltage offbias, the problem at least is found, and a solution lies near].
then start at the input with your probe.
  I've had good luck with this order of tasks, My DMM [with clip at black lead end] makes quick work of the voltage check, lighweight/handy it is].
  The DMM set to 'beep' mode can do many of the signal path 'through or block' tests [not the buffers in TS though], this may save a total patching, amp warmup/probe job too.
  Put a 1/4'' mono phono plug in the input jack to test voltages.
  It has saved me tons of hours.

[JAC JR]

For what it is worth....

I had a GGG Rodent that I spent about a week trying to "de-bug." The voltages on my IC socket were not even close to correct. After checking all my component values a number of times, and making sure I didn't have shorts I still couldn't figure out the problem. Out of desperation I remelted every connection on the PCB. It all of a sudden worked flawlessly! I recommend trying this approach.

[AppleScrappler]

thanks for all the replies so far fellow builders!  I just finished making and audio probe device and have been experimenting to make sure it works.  so far so good! 

my only issue are 1) the traces are covered by a protective layer on the underside so i'm not sure exactly how to safely remove it  (gently scraping maybe?)  or if I can just test at the solder joints along the path. 

2) I'm not entirely sure which traces to follow for the audio signal from beginning to end.  Some are obvious (like near the input and output) but following it the whole way looks like a maze to me. 

I suppose only trial and error and a stubborn resolve to get this thing fixed will guarantee success

I'm going to give it a whirl now.  Any more advice is welcome.  I've read most every debug FAQ on many sites ranging from this one to the GGG site.  I guess sometimes taking what's on paper and putting it to use is a foggy area for me.  I get in my own way by over analyzing until I confuse myself.   So I appreciate all the help guys!  I'll DEFINITELY let everyone know how things turn out one way or the other

[R.G.]

1) the traces are covered by a protective layer on the underside so i'm not sure exactly how to safely remove it  (gently scraping maybe?)  or if I can just test at the solder joints along the path. 

It's not necessary or even better to remove it. Probe the solder joints along the path. But yes, gentle scraping if you have to remove it. If you can see a copper trace running under the protective layer, a first assumption is that the copper is fine - at least until you find a different signal at both ends of a copper trace. Then you start suspecting the copper.

2) I'm not entirely sure which traces to follow for the audio signal from beginning to end.  Some are obvious (like near the input and output) but following it the whole way looks like a maze to me. 

You only need (for now) to check it at the input and output of each active device. In that case, the base and emitter of the buffer transistors, and input and output of the opamps. If you find it's missing from one of those, post it back here.

I suppose only trial and error and a stubborn resolve to get this thing fixed will guarantee success

Determination helps, always.

[AppleScrappler]

Thanks R.G.

The last place i have signal is at pin 3 of the op-amp.  i checked all the other pins (not just the out pins) for good measure and the signal does not reappear at any of them.  I assume it's supposed to exit at pin 1 and then move on to the clipping stage.  

I have replaced the op-amp and this hasn't fixed the problem.  all the solder joints have been done over too.  could the socket be broken or somehow shorting the IC out?  

[Paul Marossy]

The last place i have signal is at pin 3 of the op-amp.  i checked all the other pins (not just the out pins) for good measure and the signal does not reappear at any of them.  I assume it's supposed to exit at pin 1 and then move on to the clipping stage.

Looking at this schematic, and assuming that the PCB has Pin 3 of the opamp connected to Q1, I still think you might have a problem with the Vref supply. You would get no output at Pin 1 and everything else after that would get no signal, either.

[petemoore]

  And the voltage there  at the problem site ?
 Might as well measure all relevant pins, all, otherwise, we'll never know.
 A buffer should be right near 1:1 volume from input to output [B/E transistor probing should sound about the same volume] depending on what else is involved impedance wise, sometimes they make a touch brighter sound.
 Otherwise it sounds like the input buffer is working, but the opamp is misbiased [likely] or there's a blocked or open signal route [especially unlikely on it's own, it could be a mod solder gone bad].
 

[AppleScrappler]

Looking at this schematic, and assuming that the PCB has Pin 3 of the opamp connected to Q1, I still think you might have a problem with the Vref supply. You would get no output at Pin 1 and everything else after that would get no signal, either.
[/quote]

Yes, that's the schematic.  All the voltages check out exactly as indicated in the instructions and virtually match those in my other TS.  I've tried with battery and wallwart if that makes any difference.  What can i do to alter the vref so it's within spec - if needed?

  And the voltage there  at the problem site ?
  Might as well measure all relevant pins, all, otherwise, we'll never know.
  A buffer should be right near 1:1 volume from input to output [B/E transistor probing should sound about the same volume] depending on what else is involved impedance wise, sometimes they make a touch brighter sound.
  Otherwise it sounds like the input buffer is working, but the opamp is misbiased [likely] or there's a blocked or open signal route [especially unlikely on it's own, it could be a mod solder gone bad].
 

if the opamp is misbiased then why did it work for the first few days and then suddenly stop?  what should I do to change the bias if that's necessary?

[AppleScrappler]

So after much experimenting I decided to replace the opamp again... and now the pedal works fine.  I can't understand why the other times I switched the chip it didn't work... but now it does.  The only mystery left is why the first chip stopped working in the first place.  It was the 4558D jrc that came with the kit.  Any thoughts on why it failed?

[petemoore]

if the opamp is misbiased then why did it work for the first few days and then suddenly stop?
  The bias ~went offline and stopped the pedal.
  what should I do to change the bias if that's necessary?
  If you connect two equal value resistors across a voltage...such as the divider resistors which give you the also known as's: 1/2v = Vref = Vbias.
  If the resistors are perfectly matched...within 10% should be fine since the opamp will work when the reference voltage is held near the center of between the highest and lowest voltages [V+ and negative-Gnd.
  Any thoughts on why it failed?
  Test the pulled opamp, if it works then thinking it was something with the circuit may be the best use of time.
  ..and opamp socket lug got pushed against it's coldsolder?
  Distant point testing:
  Includes resistor, and connection and wire..anything between the two distant points:
   For instance, a transistor collector lead at one end of a DMM set to an R range of 200k, the other lead to the battery clip. This will show if there's a connection to the: Socket lug, socketlug's board trace, board trace continuity, the resistor value, the connections at both ends of the resistor, the other board trace, the connection to the batteryclip V+, the battery clip wire, clipwires connection to clip button.
 

[Paul Marossy]

So after much experimenting I decided to replace the opamp again... and now the pedal works fine.  I can't understand why the other times I switched the chip it didn't work... but now it does.  The only mystery left is why the first chip stopped working in the first place.  It was the 4558D jrc that came with the kit.  Any thoughts on why it failed?

Huh, strange. I had a circuit do something similar to me once. It only worked with one specific opamp. I couldn't explain why it was acting like that, and it's still a mystery to me even now.

[AppleScrappler]

Well guys I just wanted to formally say thank you for all of the input.  I'm still going to poke around and double check the voltages with the new chip in place to make sure they're within specified parameters, but otherwise I'm considering this case closed.  I'll admit I feel a little silly now after all I went through and what presented you guys being that the solution was to simply switch the opamp.  If I hadn't already tried that (it was the very first thing I did after checking that all the wired were attached) I'd feel really stupid now.  But in the end all that matters is that it works.  I will keep an eye on it after I give it back to my friend though... if it acts up again then I'll know something is wrong elsewhere causing the chips to fail.  Then I'll reconsider everything mentioned in this thread to try and solve the issue for good.

Thanks again for all the great advice!

[ACS]

Could it have been a bad socket for the IC?  One of my 'hygiene checks' when I'm debugging is a continuity test between solder joint, through socket, to IC leg.  Had a socket once that just refused to pass signal through one of its positions - but the voltages still looked fine!