QSC TouchMix 16 sound problem fixed (other touchmix versions may also get this)

[Rick Smith]

Is there absolute certainty that the capacitors are reversed? Is it possible that the negative side of the caps connect to pin 2 of the XLR because the 48v originates from an external source and not the TM16?

Has anyone obtained the official Service Bulletin from QSC on the capacitor issue? It would be nice to see it. Also has anyone found a service manual for the TM16 or TM30?

 

[Paul Lewendon]

Is there absolute certainty that the capacitors are reversed? Is it possible that the negative side of the caps connect to pin 2 of the XLR because the 48v originates from an external source and not the TM16?

Has anyone obtained the official Service Bulletin from QSC on the capacitor issue? It would be nice to see it. Also has anyone found a service manual for the TM16 or TM30?

3rd post down from the beginning explains it. And it's not every one of them, just certain versions before they caught it, so make sure before just changing.

 

[Rick Smith]

Thanks for your reply. I did read and understand the entire post. But my concern is that this post seems to be the only source of information on this issue that I can find. And to be clear, my intent isn't to challenge anyone's character, but rather to authenticate the information before I modify the several mixers that I own. Two of them had swelled caps. So as prevalent as the issue seems to be, you'd think there'd be more out there besides this post and videos instructing how to replace the caps (in the same orientation). I just put a call in to QSC in hopes to get confirmation directly from them. The rep I spoke to was unaware of the cap issue on any boards manufactured, but assured me that he'd research it and get back to me with an answer.

 

[Paul Lewendon]

Yes I know what you mean, it's understandable, it seems like a big error, and head scratcher how it left the design, factory, etc. without being caught.
Any repairs they'd just swap the board, and problem solved.
The thing is that with most things these days, just like automakers with recalls, etc.. Admitting a problem opens you up to liability.
As long as there's no phantom power hooked up to the outputs instead of the input, the problem won't show up.
After he mentioned that, after I had already fixed ours, I took that one and another couple apart, I compared them and they look almost identical, except the markings, when I measure the continuity, it confirms what was said.
Putting reverse voltage to a capacitor will make a cap go bad.
If you have full control over your equipment and prevent power to be hooked up there, you'll be ok.

 

[Paul Lewendon]

To add a bit more to this story - we have a TM8 that was exhibiting the same problem. Low and uneven frequency response on Aux 3. I found this thread and took ours apart to find bulging blocking caps. Here's where things get interesting: I spoke to a friend of mine who does authorized service for QSC. Apparently in early production units of the TM's, the circuit boards were labelled backwards for the blocking caps, so although they appear to be installed correctly, they are backwards, meaning that if you send any of those outputs into a console with phantom power on, there's no blocking going on and the caps will fry.
So if you go to the effort of replacing the caps, check to make sure they are in correctly (positive side of the cap should make continuity with pin 2 of the output XLR - ours are backwards currently).

Hope that helps anyone else with this problem.

Cheers,
Brian

New problem caused by these bad caps, it sounds like a train going down the tracks just in hearing distance, fine on Aux out.
This is another one of our touchmix-16 units with bad caps and I did a continuity check, and sure enough the negative was at pin 2, but I was expecting the + of the cap to be at pin 1(ground), so for blocking it's a in series cap the signal just passes through, not attached to ground(parallel). It fixed the train noise problem.

 

[Alessio Ciccone]

Salve a tutti, stesso problema di volume basso da main right, ho controllato i 2 condensatori in uscita e sono ok.
Quale può essere il problema ?
Grazie in anticipo !

 

[Paul Lewendon]

Salve a tutti, stesso problema di volume basso da main right, ho controllato i 2 condensatori in uscita e sono ok.
Quale può essere il problema ?
Grazie in anticipo !

I used Google translate. So the caps were ok, only one channel has low audio or do both have problems ?
Try doing a factory reset.

 

[Alessio Ciccone]

I used Google translate. So the caps were ok, only one channel has low audio or do both have problems ?
Try doing a factory reset.

Grazie! Già fatto reset di fabbrica, il canale basso e solo uno, main right

 

[Paul Lewendon]

Grazie! Già fatto reset di fabbrica, il canale basso e solo uno, main right

If you have already did a reset and checked the capacitors, it looks like you have deeper problems, could be a few different components,
check to see if there's anything burnt, or if you have a multimeter, do comparison tests between channels.

 

[Alessio Ciccone]

If you have already did a reset and checked the capacitors, it looks like you have deeper problems, could be a few different components,
check to see if there's anything burnt, or if you have a multimeter, do comparison tests between channels.

Sicuramente un problema più serio, speravo qualcuno avesse già avuto questo problema e che poteva consigliare le possibili parti guaste da sostituire

 

[Roy Andrews]

Sicuramente un problema più serio, speravo qualcuno avesse già avuto questo problema e che poteva consigliare le possibili parti guaste da sostituire

Check post #27 where I discuss an additional problem I discovered after replacing the caps that resulted in lower than expected volume on one channel of the mains. Summary... tiny surface mount resistors could be bad or damaged.

 

[Alessio Ciccone]

Ok! Credo di avere trovato la causa!
Ho fatto delle prove di comparazione di tutti i componenti col canale funzionante, è solo questo jfet da valori diversi !
Qualcuno sa darmi i valori per poter ordinare il nuovo jfet ?

 

[Alessio Ciccone]

Ok ho risolto! Ho staccato il transistor bruciato dal canale AUX 4 (che non utilizzo) e l’ho sostituito con quello bruciato su MAIN RIGHT ! Ora tutto funziona! Spero sia utile ad altri col mio problema!

 

[Roy Andrews]

Based on the 41* code, it looks like this might be a P-channel MOSFET, and might be one of the following 3 devices - for those not aware, SMD packages do not have enough space to etch a full identifier, so typical identifiers are 1-6 alpha / numeric characters, which then need to be decoded to a full part number using some internet database. This can lead to more than 1 possible match when no schematic / parts list is available:

TSM3401CX

AFP2341

GSM2341

I remind everyone that NO schematics for the Touchmix family have ever made it to the public domain. And of course, if you happen to work at a QSC authorized service center and would like to accidentally drop a schematic on ManualsLib or someplace like that, well, we'd all be eternally grateful.

 

[Paul Saini]

Hi,

Anyone know why I don’t get any output at all from any of the Auxes or the Mains. Checked the caps and they all look fine on the outputs. Not sure where to go from here.

 

[victor koay]

I fixed a problem likely heat related, as these things run a bit hot.
I hope this post helps people having a similar problem as boards are all just replacement these days, and that's pretty much the whole unit.
Note: Read the 2 addendums below from Brian.

I got one of our touchmix-16 units in the other day and had to fix a low and missing some sound frequency on the right channel, I tried resetting everything just to start from scratch, but it didn't help. swapping channels(in and out) it followed it just on output. It didn't seem to appear on headphones. For some reason it was effected by the L,C,R adjustment even though I didn't expect that, but I don't have the schematics/block diagram to see how it effects it. These things do run a little hot with no fan and not much ventilation. I took the unit apart and most of the capacitors at the back of the unit along the AUX inputs and main outputs were slightly mushroomed on top (47uf/63v). Usually in electronics it's the caps in the power supply that do that, but this seemed to just be signal. 6 mushroomed of the 10 caps in the area were reading around 16uf, so I replaced all 10. It totally fixed the problem. I didn't test the Aux before taking it apart, but I'm sure they were effected as well.
I put the same temperature rating in from my stock, but probably best to find higher temp rating to help prevent it, or at least make it last longer.
I don't have the schematic to see exactly what all of the capacitors did, but I think most were just signal related.
If you're handy you could probably add a tiny fan off the supply in since those fans are such low power drain.
Normally our units aren't used every day, but I think this one was in a studio we had built(gone now) and was running
for probably a year and a half straight but only used maybe 1 or 2 days a week. For some reason some techs don't feel the need to shut thing off when not used every day.

Hi Paul,
I got a Touchmix 16 unit, running for a few years without any problems, recent lossing of low frequencies , further check from the main output (left and right), monitoring and headphone sound good.
Do you have the schematics diagram? is it possible the output caps problems?
thank you in advance

 

[Roy Andrews]

Hi Paul,
I got a Touchmix 16 unit, running for a few years without any problems, recent lossing of low frequencies , further check from the main output (left and right), monitoring and headphone sound good.
Do you have the schematics diagram? is it possible the output caps problems?
thank you in advance

As I said literally 2 posts above, there are NO schematics for this device in the public domain. We would all love for somebody working at a QSC authorized repair center to accidentally upload the diagrams to somewhere like ManualsLib, but I'm not holding my breath.

I believe that it is entirely possible that your issue is caps related, because my first experience with the caps issue was on a Touchmix8, which initially had weak bass, then after sitting unused for the entire pandemic had no output at all & was suffering from bulging caps when I opened it. Also, the TM16 runs very hot, so if you leave it on for long periods, like in a studio or something, then those caps are getting baked every day, which shortens their working life. And worth remembering that when these units are SOFT powered off, as opposed to having their plug pulled out of the wall (or turned off via a power strip), they are STILL generating plenty of heat as you can easily verify by touching the bottom of the mixer. For the longest life & best user experience, ALWAYS hard power off & leave disconnected until actually needed.

 

[Peter Gaff]

Hi, have a TM16 SN: LLE0G266. Caps are bulged and mains are noisy. Thank you for posting this issue.
Because there are 2 caps on the mains I was checking which pin connected to what.
Looking at the bottom of the board with the output XLR's to the top, Right or Left Main, the Left Cap, right leg goes to XLR pin 3, while the Right Cap, right leg goes to XLR pin 2.
Does this suggest that the left cap should be the opposite polarity of the right cap being that XLR pin 3 is the - signal or just reverse both of them?
Thanks

 

[Paul Lewendon]

Hi, have a TM16 SN: LLE0G266. Caps are bulged and mains are noisy. Thank you for posting this issue.
Because there are 2 caps on the mains I was checking which pin connected to what.
Looking at the bottom of the board with the output XLR's to the top, Right or Left Main, the Left Cap, right leg goes to XLR pin 3, while the Right Cap, right leg goes to XLR pin 2.
Does this suggest that the left cap should be the opposite polarity of the right cap being that XLR pin 3 is the - signal or just reverse both of them?
Thanks

Chances are if one or more caps are mushroomed on top(not flat), then the caps need to be replaced and reversed, but not just the 2 that are bad, but all the Aux inputs and the 2 mains. It will save you time not having to take it apart a second or 3rd time.
Note, it's just those, not all on the board
Post#18 has a pretty good explanation with pictures.T
Here is what a good one looks like with caps in the proper direction.

 

[RUDOLPH GAROA]

Hi there, For that part of your comment where the Touchmix 16 was running hot, I had the same problem with mine sometime last year. Where it would get really hot even to the point of cutting off. It seemed like the power supply for the unit was playing up. So I replace the cable connecting into it's power supply going to the wall outlet. This solved the problem totally. They do get hot, but very slightly but nothing compared prior to the changing of the cable. My lesson there is "don't take anything for granted"... : )

Regards,
Rudolph

I fixed a problem likely heat related, as these things run a bit hot.
I hope this post helps people having a similar problem as boards are all just replacement these days, and that's pretty much the whole unit.
Note: Read the 2 addendums below from Brian.

I got one of our touchmix-16 units in the other day and had to fix a low and missing some sound frequency on the right channel, I tried resetting everything just to start from scratch, but it didn't help. swapping channels(in and out) it followed it just on output. It didn't seem to appear on headphones. For some reason it was effected by the L,C,R adjustment even though I didn't expect that, but I don't have the schematics/block diagram to see how it effects it. These things do run a little hot with no fan and not much ventilation. I took the unit apart and most of the capacitors at the back of the unit along the AUX inputs and main outputs were slightly mushroomed on top (47uf/63v). Usually in electronics it's the caps in the power supply that do that, but this seemed to just be signal. 6 mushroomed of the 10 caps in the area were reading around 16uf, so I replaced all 10. It totally fixed the problem. I didn't test the Aux before taking it apart, but I'm sure they were effected as well.
I put the same temperature rating in from my stock, but probably best to find higher temp rating to help prevent it, or at least make it last longer.
I don't have the schematic to see exactly what all of the capacitors did, but I think most were just signal related.
If you're handy you could probably add a tiny fan off the supply in since those fans are such low power drain.
Normally our units aren't used every day, but I think this one was in a studio we had built(gone now) and was running
for probably a year and a half straight but only used maybe 1 or 2 days a week. For some reason some techs don't feel the need to shut thing off when not used every day.