microfonic on fender frontman 212r

[hutsch]

hi everybody
I'm having a little bit of trouble in a frontman 212r amp.
It's working normaly but with some microfonics issues.
Its is not to much, but when u use the drive channel u could fell that little sound on the amp.
I started to check if its a problem of the circuit, but i don't know where to start.
Could it be a circuit problem ?
Any suggestions?
thanks

[JoeM]

Is it still under warranty?

[hutsch]

Is it still under warranty?

no I have to repair it, but never did any repair in this fender.

[Chuck H]

Is it "microphonic" without an instrument plugged in? That is, does the amp begin to feed back all by itself with nothing in the input?

[Alan0354]

What do you mean by microphonic? feedback, wanting to start squealing? If only happen with guitar plugged in, it might be your guitar. Some pups are not potted. Give more description on the condition first, don't assume anything.

Slap the amp and see whether you can hear anything to do a rough check for cold solder.

[JoeM]

Yes, you need to be a bit more specific what you mean by microphonic. You're not referring to some kind of cabinet rattle or vibration by any chance?

[hutsch]

the thing is that its microfonic with the guitar plugged on, my client told me that the amp started to do this after some time he bought it, i tested with my guitar and i didnt see to much problem on it, but i notice on the back of the sound, a very thin sound like a whistle, and when i cut all the sound of the guitar, the whistle remains , very low sound, but annoying.

[Jazz P Bass]

Do any controls affect the "whistle"?
Break out your scope & find where the whistle is coming from.

[Chuck H]

A "whistle" is often a ceramic disc cap. You can try opening up the amp and set it up to cause the problem, then touch components with a wooden stick. If touching a component stops the noise then replace it with a higher quality part. But...

If the owner has a problem with his guitar, that you don't have with yours, it could be a guitar related issue as well. Have your guy set up and show you the problem so that you can determine if the guitar pickups are squealing. It's also possible that the owners guitar and the amp sort of resonate together more than your guitar and the amp, excacerbating the problem. I think the owner should give you a demonstration.

[Alan0354]

If you can hear the whistle sound, that should be easy to find. But....

Have him show you with his guitar before opening anything up. Try slapping the amp as see what happen. Just a rough check for anything loose. When you open the amp, then use a wood stick to tap the components and connectors.