Fender FM212R switching prob.

[jbmdisco]

Hi,
Have one of these in today with the channel switching fault. Metered out the usual suspect resistors both showed as good. However these have been previously swapped out so I decided to remove, clean the legs and refit as the soldering looked a bit 'off' - more blobby as flowing. As I cleaned the pads to refit one came clean away from the board. I am now suspecting that there was an intermittent contact between this and the track causing the fault. I tried the amp for a good hour or so before proceeding but couldn't get the fault to occur. The other problem this amp had was a broken clean channel volume pot which the owner said stayed in one position and has been for the last year . This fault was highlighted when unscrewing the nut and the pot disintegrated
RE- switching fault : is there any other common fault which would give the same symptoms of the changing channel fault ? The owner did ask if it would be possible to have the amp permanently switched to clean as this is all he has ever used.

[DrGonz78]

When you say channel switching fault what do you exactly mean? Stays in dirt drive mode only and clean is shunted off always, does more drive switch? I think that is what you meant, but I am a little confused. Is this with the foot switch connected or not, both? I can attach the schematic but I am not sure which resistors you are referencing. Just need some more info to clarify. Actually I am getting the impression that you fixed the switching fault already?

[52 Bill]

I don't think that there are any "typical" problems with these amps, other than the usual things that are common to all amps of similar construction. Parts come loose, traces break, etc.

This is one of the many non-serviceable amps from Fender, so there won't be a lot of info out there. I fixed one before I knew that we weren't supposed to fix them, coil on the output line broke loose. A few have come in out of warrantee, with similar problems, loose power resistors, bad speakers, etc.

[olddawg]

I picked one of these up in like new condition with the foot-switch for $35. I was surprised at how good it actually sounds. It has a very annoying and intermittent loud pop which I suspect is the diff pair imputing the power amp and it hasn't been a priority, lol. I have fixed several of these for local musicians where the main power supply filter caps have simply fallen out. The Raggae guys like them. If you are having switching problems the first thing I would check is your rail voltages for symmetry and ripple. A scope is pretty much essential for SS amps.

[MandyWeidemann]

When you say channel switching fault what do you exactly mean? Stays in dirt drive mode only and clean is shunted off always, does more drive switch? I think that is what you meant, but I am a little confused. Is this with the foot switch connected or not, both? I can attach the schematic but I am not sure which resistors you are referencing. Just need some more info to clarify. Actually I am getting the impression that you fixed the switching fault already?

i kept this pdf...it's good...and i agree with you...can you tell more details as i am confussed too...

[J M Fahey]

i kept this pdf...it's good...and i agree with you...can you tell more details as i am confussed too...

Generic robot generated answers 101 .

[g1]

That's definitely not this Mandy's blog, the blogger has some grammar skills.