Tech 21 Trademark 60 Noise

[Lobsterjoe]

Just got an '06 Trademark 60.  At power-on, there are continuous popping and whooshing noises.  Consistently, it goes away after about six minutes.
Power cycle and the noise returns but then lasts less than a minute; unless the amp's been powered for an hour or more-then it's fine after restart.
All other functions work and amp sound normal except for addition of noise.
If I plug guitar into the effects return, the noise stops and guitar sound is fine.
Cleaned all the jacks, visually inspected PC board, jumpered the FX loop jacks (no effect on noise).
Channels settings, boost level and reverb level don't affect the noise level, but master EQ does. The character of the noise doesn't change-just how loud it is proportionate to the EQ cut or boost.
Tech 21 was responsive to my inquiry and said they haven't seen this before. Suggested I send it in. Being in California, the round trip shipping even for chassis only will be almost as much as the bench charge. Reminder: other than switches and some caps/IC's, most of the components are SMT. Comments welcome.

[g1]

I don't think they will provide any service documentation for anything they make, even to dealers.
For that, and the SMT issue, you pretty much have to send to them or their authorized station.
But I would check with them whether you could send the board rather than the chassis.  That would save a lot of weight for shipping.

[Lobsterjoe]

They quote $80 an hour.  Not sure the additional time for them to connect and disconnect from a chassis (or test rig) at their shop would be less than the shipping.  Shipping charges will likely be based on dimensions anyway, so additional weight of full chassis might not be a big cost difference.

[phatt]

You may have a dry or cracked joint somewhere. Get a wooden skewer stick and start gently probing and prodding around the PCB, large components are more prone to cracked solder pads.
Phil.

[joecool85]

Just got an '06 Trademark 60.  At power-on, there are continuous popping and whooshing noises.  Consistently, it goes away after about six minutes.
Power cycle and the noise returns but then lasts less than a minute; unless the amp's been powered for an hour or more-then it's fine after restart.
All other functions work and amp sound normal except for addition of noise.
If I plug guitar into the effects return, the noise stops and guitar sound is fine.
Cleaned all the jacks, visually inspected PC board, jumpered the FX loop jacks (no effect on noise).
Channels settings, boost level and reverb level don't affect the noise level, but master EQ does. The character of the noise doesn't change-just how loud it is proportionate to the EQ cut or boost.
Tech 21 was responsive to my inquiry and said they haven't seen this before. Suggested I send it in. Being in California, the round trip shipping even for chassis only will be almost as much as the bench charge. Reminder: other than switches and some caps/IC's, most of the components are SMT. Comments welcome.

Given that the noise is modified by the tone stack, that means that it is happening before this point in the circuit.  Starting there (at the tone stack), working your way backwards towards the input jack.  Something between here and there is either fried, or has a cold solder.  Odds are it is a cold solder.  Careful inspection of the potentiometers as well as any caps and ICs that are through hole components in this area (between input jack and tone stack) and I think you'll find the issue.

You can also share close up pictures of the board and we'll see if we can help.

[Lobsterjoe]

So the noise this TM 60 was making has mostly stopped: none on boot up; occasional very low level while playing, but thay may have stopped too.  In fact I used on a gig last week.  IS it possible that an electrolytic cap gradually reformed during use?

[g1]

Yes, it is possible for electrolytics to self-heal.  Whether it is temporary or permanent is another question.   

[Lobsterjoe]

Had a Marshall 5203 SS Combo that did similar things.  The guy I traded it to, said noise stopped as he was firing it up every day...In both cases the amps had not been powered for a long, but unspecified, length of time.