Fender FM 212R dead

[anelles]

I've got a Fender FM 212R that's been taking up space for too long now, I want to get this fixed and sell it. I bought my FM 212R around 03-04, the first one died after 2 months of use, Fender paid to have it shipped back and either repaired or replaced it, not sure.

After the initial problem, the amp worked flawlessly for about 5 years until it croaked. I built a '65 Deluxe Reverb kit shortly before the FM 212R died, so I haven't been to motivated to repair it.

The problem: When I turn it on, I get a low pitched, constant tone. Volume knobs do not work, tone knobs have no effect on the constant tone either. Adjusting any of the knobs has 0 effect.

I've opened it up and everything visually appears to be ok. Any suggestions on what components to check first?

[Enzo]

They replaced it, they didn't repair it.

Low pitched constant tone, eh? Pretty loud tone?

One of two things probably happened. Either the amp has blown or one of the filter caps cracked free of its solder.

First, WATCH the speaker cone when you turn it on. Does it move one direction and stay there? If so, turn it off NOW. The cone staying at the extreme means there is DC coming from the amp. That means something has blown, and it also will damage the speaker if left running.

If the speaker stays at its rest position, then the amp is not making DC, and the filter cap is not working. Most likely because it has cracked free of its solder underneath. The main filters are the two largest cylinders sticking up off the board. Wiggle them while it is running, if the hum comes and goes, resolder them. One COULD be bad, but probably not.

If the amp has blown, there are a few relatively recent threads on this board about the FM212R and repairs to it. Please find those threads and read through them for some insights. That should save us going over the same stuff again. But we'll do whatever we can either way.

[anelles]

The speaker pushes forward and stays. I don't think it's ever been allowed to hum for more than 5sec at a time, only a few times, so hopefully the speakers are unharmed.

I'll search for some older threads.

[Enzo]

Then the output stage is "blown." That doesn't mean any specific failure, just that something has failed causing DC on the output. Potentially: shorted output transistors, missing power supply voltage, shorted smaller transistor, etc.

[anelles]

Sounds good, when I get it on my workbench I'll check the transistors for shorts and see what the transformer is putting out.

[Enzo]

Oh, the transformer is probably just fine. The same winding creates both positive and negative DC for the system, so if one supply is missing, it won't be because of the tranny.

[Ronsonic]

Sounds good, when I get it on my workbench I'll check the transistors for shorts and see what the transformer is putting out.

Let me just say that when these were new Fender had them on the "No Fix List" IOW they would not pay a service center to perform repairs in the field. This is ATMO an admission that repairing them is not very profitable. Soldier on if need or curiosity drives you. Do know that these are fragile, crappy boards with feeble traces and a circuit that will require very complete repair and troubleshooting lest it destroy yet more parts as you walk in on a repair.

[Enzo]

Like any manufacturer's do not repair list, it reflects the cost of the item. Warranty repairs are never profitable, they are always an expense. The expense of paying a repair center is higher than the expense of replacing the amp in these cases. A warranty claim costs a predictable amount. If they pay me $50, plus it costs them $20 to process it and mail out a check, plus parts costs and shipping on them, that adds up. So there is a threshold of say $85-90 dollars. Any amp they can replace for less than that goes on the list, regardless of how good a quality the parts are or are not.