crate GTX 212 wavering hum

[chateau]

Got this gtx212 for $50 and it has this very noticeable hum after plugged into. seems to function fine. but have volume up to drown out the hum. Had the head completely down and inspected all the boards with a magnifying glass, all good . checked the grounds and the input and tried the red wire loom relocate with a tiny bit of improvement. Guitar and cord are good. This amp does way more than my little fender champ tube amp. Would really like to get this crate right again. Help needed!

[Jazz P Bass]

Well to the forum.

A number of things could be causing hum.

First up is the power supply filtering.

Do you have a volt meter?
If so test the power supply voltages for symmetry & lack of Vac ripple.

[52 Bill]

Help needed!

Welcome to the place.

You need to give us some more information in order for us to help you. There were a few different models of that amp, so if you go to NickB's site you will find the schematic for it there. https://bmamps.com/Schematics/crate/...tx_212_sch.pdf

Compare the amp with the schematics and tell us which version you have.

Is the hum always there as soon as you turn on the amp? Is it there when there is no cable plugged into the input? Do any of the volume or tone controls change the tonal character of the hum?

What sorts of test equipment do you have available for your troubleshooting investigations?

[chateau]

There is no hum until I plug into the amp, no change with any volume control. I have a volt meter and ohm meter.
serial# on the back of the amp is A s030303, 11/20/03 1st eng. model made in china

[Enzo]

If there is no hum until you plug in, then I would look at the input jack itsel;f, are the ground connections solder cracked? Try just resoldering all the point of the input jack. Or possible bad jack. otherwise it points to a problem being outside the amp.

[52 Bill]

If you plug your guitar into the insert jack, it will bypass the entire preamp. If you do that is the hum still there?

[chateau]

If you plug your guitar into the insert jack, it will bypass the entire preamp. If you do that is the hum still there?

Yes the hum goes away

[52 Bill]

Did you check the input jack as Enzo suggested?

Sometimes if you lightly push or pull on the phone plug it will move the jack enough to make or break a connection. If that doesn't work, then you will have to remove the chassis from the cabinet to inspect things. Do you have any experience with working on amps? Do you have any test equipment?

[chateau]

Did you check the input jack as Enzo suggested?

Sometimes if you lightly push or pull on the phone plug it will move the jack enough to make or break a connection. If that doesn't work, then you will have to remove the chassis from the cabinet to inspect things. Do you have any experience with working on amps? Do you have any test equipment?

I have had the chassis out and checked it over with a magnifying glass , the input jack is good, no cracks on any of the soldering anywhere. Did take it to TV, radio ,audio tech and he determined that the DSP board was faulty. Haven't been able to locate the exact one. The # on mine is 06b885-20. Found a -14 & -15 . The -14 looks close and might or may not work. I am at best a novice at amp repair. Did replace a caps can in my little fender tube amp. Hoping to find the correct effects board at this point. I appreciate your response .

[chateau]

Are there tech's out there that could check dsp board out? It looks like new physically , Maybe one of those little cans went bad, can't find a burned resistor .