Frontman 212R no output on drive channel

[bnwitt]

I just received a Fender frontman 212R for repair with no output on the drive channel. The normal channel sounds fine and the reverb works when in the normal channel mode.

However, if you swithch to the drive channel with the panel button or the footswitch, the amp goes silent. Does anyone have a schematic on this amp? I'm working off the non-reverb one at the moment. I'm going to pull the chassis and look for obvious problems.

[black_labb]

i had an issue with one, and couldnt find the schematic either. my issue was the resistors dropping the voltage, but yours wouldnt be. sorry i couldnt be any help

[bnwitt]

I appreciate the response black_labb. I did find a schematic for an FM212R so I'll attach it for you. Looking at the schem, there are any number of devices that could fail and drop the drive channel signal including several jfets, opamps and the contour switch along with many others. Here's the funny thing. I just played with the contour switch a little and the drive channel came back on. I'm going to pull the chassis and check all connections.

[bnwitt]

Ok, now I have a question for anyone familiar with this amp. It looks to me like the drive channel when turned on just swamps out the signal for the normal channel and doesn't actually switch the normal channel's output off. Is that the case?

[Enzo]

Looks that way, unless the gate circuit of Q5 is totally mis-drawn.

[bnwitt]

Sort of makes you wonder why Q5 is even there if it is really wired that way. Wired differently with the gate controlled by the channel switching it would shunt the signal to ground right?

[Enzo]

I have no idea what Q5 is all about as drawn.

[bnwitt]

I have no idea what Q5 is all about as drawn.

Well then there is no hope for me to understand it. Obviously it is drawn wrong.

[Enzo]

Sure you can. Find Q5, and the gate diode D9, on the board. Follow the traces from the cathode of D9 and see if it actually goes to C10 like the drawing, or if it instead connects to the DRIVE-SEL line.

Actually, don;t bother to trace it, just measure continuity from cathode of D9 to negative end of C10. COntinuity or not? Then measure from cathode D9 to some point on the DRIVE-SEL line like the cathodes of D11 or D14. COntinuity or not. No need to flip the board.

[Mars Amp Repair]

As an aside,
Did you know that Fender no longer authorizes warranty repair work on the FM212?.

They send an exchange amp. Wild to think it's cheaper for them to ship one of these & pay to have the defective one shipped back to them, then to have me fix it for their measly $50.00.

Surprized (and disappointed) the heck outta me...glen

[bnwitt]

Enzo,
Unfortunately the amp is back in the hands of the owner after cleaning the Mid Contour switch, everything was working fine. If it comes back in I'll trace things out.

Glen,
I had heard that. It doesn't make a lot of sense unless the failure rate is really low and they've not been happy with the quality of warranty repairs from authorized service centers. I would think sending a new amp might not fix the problem when it is something connected to a design issue that has not been corrected with a redesign. They definitely lose the field tech feedback aspect that way. From what I've read in this forum and others this seems to be the way of future for alot of manufacturers. Thank goodness for warranty expiration dates.

[Enzo]

The FM212R is about the largest throw-away Fender. There was also a bass combo, a (something)60 that surprised me the first time.

They don't pay us $50 because the amps are so inexpensive and profit margins so low. It makes more sense to their bottom line to send another amp.

I do note that the little Frontman practice amps and similar, they don;t want back. The FM212R last time I did one, they sent a call tag for it.

[Mars Amp Repair]

BTW...the new Peavey VYPR 1x12 combo looks alot like a Beringer inside. Only 3 pcb's that look unservicable...REALLLLL JUNK!

fortunately (I guess), PV just does board swaps on these little 'gems'. Makes me sick that this once proud American company has had to stoop to making this garbage... economics & all.

I hope the better ones remain quality & don't all go this route for Peavey. g

[Mars Amp Repair]

Enzo...that's the Rumble 60 you're thinking of...g

[bnwitt]

Well I just finished servicing a TOA A-912MK2 P.A. amplifier and I was blown away by their quality. The unit failed after a power outage due to a spike and the power board fried. Excellent construction inside and easy to service. I ordered the power board and it came in a composite break apart that included the condenser rectifier board, the output jack board and the LED MV board. All for a very reasonable price. Some American companies are still doing the right thing.