Replacing Power Amp in Fender FM212R

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This is Pro Audio?

You have a lot more experience but I've had some surprisingly low prices for board-level replacement, but I guess not if it's all one board; it sometimes pays to ask.

When you get to the consumer-grade mixers I've found worn pots printed directly on a board, or a scorched board full of SMD devices that left carbon deposits and replacement of the whole mess is your only affordable option. Bose had a power-amp board exchange that was pretty cheap. Warranty TV repair nowadays is pretty much running a self-diagnostic and board-level replacement.

But I've never even seen inside one of these so I defer to you of course.
 
CXrap, I had a nice response typed in then typo'd a screen clear. Grrr...

Pro audio simply refers to the use, not the cost. This amp is surely as entry level as it gets, but it is intended for stage use, no matter how informally we mean that, as opposed to something for the home.

At the scale of TV sets - made by the millions - they can make boards of various types cheap and swap them out. That might be common in consumer goods. But someone like Fender will be expecting component level repair. As a fold level Fender tech I am authorized to spend up to two hours on a warranty repair. I suspect Sony or Bose would not allow so much labor on one of their consumer units. I might be wrong.

yeah, I remember long ago Alesis made some god-awful mixers with painted on pots. Once they wore out, there was nothing to repair there.


I know there are guys buying new boards for some Marshall amps. They may find $250 or whatever a good price, but if I took in a $300 amp, replaced a board in it, let us say a $150 board to be VERY generous, and $100 for the work, we are up to $250 for the repair, which will price most of th owners out of the repair. And that assumes my new board only cost me like $75. If I pay $150, I have to mark the board up, and I can quickly exceed the replacement cost of the amp.
 
I suspect Sony or Bose would not allow so much labor on one of their consumer units. I might be wrong.

I can't comment on Bose, but unless it's different in the USA?, Sony (and all other domestic electronics manufacturers I've done warranty work for over the years) simply pay a smallish fixed labour fee - doesn't matter how much time you spend on it, you get the fixed rate and that's all.
 
That makes sense, and I suspect it is predicated on a small amount of labor time.


I had a large PA/recording mixer a few years back, and had to replace all the ribbon cables within under warranty. I counted 960 knobs, over 250 jack nuts, 150 small screws for XLR mounting, and a lot of other hardware that had to come off to extract the boards, then put back together with the right color knobs where they belonged. Just that disassembly and reassembly took two solid hours of work. I expected to get paid for it.
 
I had a large PA/recording mixer a few years back, and had to replace all the ribbon cables within under warranty. I counted 960 knobs, over 250 jack nuts, 150 small screws for XLR mounting, and a lot of other hardware that had to come off to extract the boards, then put back together with the right color knobs where they belonged. Just that disassembly and reassembly took two solid hours of work. I expected to get paid for it.

I know what you mean :D

I repaired a small mixer (16ch?) for a 'friend of a friend' - it takes forever to just take the knobs and nuts off.

Interestingly the fault was that a number of the channels didn't work - and I found they were all grouped together, and the fault was a load of smashed potentiometers. Checking further I realised they were smashed in an exact circle - and I concluded it had been hit by a ball (knocking the shafts downwards, smashing the carbon tracks in the pots).

When the lady collected it (she was VERY attractive as well :D) I asked about the damage - which she denied. So I asked if she had a son?, she said she had - so I asked where the mixer was stored, in her conservatory - next I asked does her son play football? :D

When she left she was going to have words with her son about playing with a football inside the house :p

However, as for 'getting paid' for long warranty work, you have the option to become a service agent or not - fixed labour prices are universal in the TV trade here :(
 
True, though I suspect the labor times are larger than in consumer stuff.

For my shop, I look at warranty as advertising. Some pay OK rates, but the ones that pay cheap, at least I get customers who never heard of me finding my shop because I was on the warranty repair facility listings. So now they remain as customers for all the various services I can perform for them. IF a warranty claim beings me up $20 short of a cash repair, I look at it like that new customer only cost me $20. My $50 a month ad in the phone book never did that well drumming up new customers.
 
Okay, I've built a light bulb limiter and installed a new fuse so I think I'm ready to try and power it up again. I also disconnected the speaker load and don't have anything going into either input. Should I bolt the board to the chassis and power it up or leave it off and do something else first?
 
Start by measuring and replacing as suggested in post #13 .

The bulb limiter and new fuses won't magically repair your amp ;) , you still have to do all the hard work.

All they'll do is avoid your hard work going skywards in a puff of smoke if you forgot or didn't notice some small part ... which is the normal way things run.

But at least you'll have a second chance to find whatever is still wrong :)
 
There is nothing in a circuit that can make a shorted transistor look like it is not shorted. So if you test a transistor in circuit for shorted, and is says not shorted, then we can accept that. SO I always check them in circuit first.

That alone doesn;t say the part is GOOD, just it says not shorted.

The opposite is not true. There are plenty of things in a circuit that can make a transistor LOOK shorted when it is not. That is when we must remove the part. If it looks shorted in circuit, then we remove it for further testing. It then either is verified as shorted, or it seems OK, meaning something else in the circuit is shorting across that part.


And don;t assume there is only one way a transistor can fail. Shorting is only one possibility. Plus, while some parts will wholesale short fight out, some will be OK at the low voltages of your meter, but will fail as soon as any load is put on them.
 
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