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 Fatman Repair 
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Joined: Sat May 22, 2010 4:49 pm
Posts: 2
Post Fatman Repair

I recently inherited a Fatman rack unit from a friend, but it will not power up. The previous owner told me that it had a faulty transformer, so my friend and I tested it, and that seemed to stand up. So I connected a new one in this weekend, it was 1200 instead of 500 ma, but I didn't think that would be a problem. The unit powered up for a moment, then the new transformer failed. Any ideas as to what might be going on?

Sun May 23, 2010 1:45 pm

Joined: Thu Sep 24, 2009 2:14 pm
Posts: 99
Post Re: Fatman Repair
Check out this PaiaTalk comment:

It refers to this Scott’s Fatman troubleshooting pdf:

First off, check the 3 regulators.
First--Check for proper orientation.
There’s a +8 (IC20), a –12 (IC14) and a +5 (IC19) regulators.

It’s possible that one or more are in backwards and are sucking down
the transformer’s voltage. Or, one of the capacitors in the pwr
supply is reversed or shorted. Check C26, C27, C30, C31, C32.

Maybe pull out the regs.
Then check the voltages at + of C26, at – of C27 and + of C30.

Might be a good idea to remove the other IC’s until the power supply is working properly.

See Scott's uploaded 200dpi scan of the Fatman manual if U don't have one.

Get that PaiA Phlying! 8-)



Sun May 23, 2010 10:41 pm
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Joined: Sun Nov 09, 2008 2:49 pm
Posts: 733
Post Re: Fatman Repair
Thanks Tone.

Also, check the power switch. They can be damaged from heat during soldering and if the terminals look crooked or wobbly this is probably it. The misaligned terminal can come in contact with the metal bushing and panel and audio output connector sleeve putting the two transformer wires in contact with each other. This SinglePoleDoubleThrow SPDT mini-toggle switch should be readily available at local shops.

The fin/clip-on-heat-sink on the 7805 voltage regulator tilting over and touching the twisted resistors can cause power trouble. The tab on this positive regulator is ground and the twisted resistors have the positive power supply voltage on them. The 7912 negative regulator has the negative supply on its tab so it shouldn't contact the other two which have ground on their tabs.

Adding a connector for the power source can cause trouble if the two terminals aren't isolated from the chassis: The AC voltage could short to the neutral wire via the chassis connection with the 1/4" output connector sleeve terminal (ground/circuit-common).

Scott Lee

Mon May 24, 2010 3:15 pm

Joined: Sat May 22, 2010 4:49 pm
Posts: 2
Post Re: Fatman Repair
Thanks! I tested the leads on the voltage regs and found that the "lead C" and "V In" on IC14 were shorted. Is it reasonable to assume that this is the cause of the problem? There's no heat sink fin on that IC either.

Do I need to replace IC14 and, if so, how can I get that part?

Thanks for your help!


Sat May 29, 2010 6:32 pm

Joined: Thu Sep 24, 2009 2:14 pm
Posts: 99
Post Re: Fatman Repair
This certainly can be part of the problem, but maybe not ALL of the problem.
These little 3-terminal regulators cost about 35cents. The 5V and 12V are most common. Probably RadioSH** has them(?)

But wait......
Are U familiar with removal/replacement of an IC from a printed circuit board(pcb)?
Do U know how to test the regulator after U get it out?? These regs are pretty sturdy little beasties and have built-in thermal overload. They can take a licking and still keep ticking!!

I would say that it would probably be faster, and ultimately cheaper in the long run, to send your Fatman back to Scott. He can test EveryThinG and fix whatever was damaged.

That way, when U get the Fatman back, it's ready to make music!! 8-)


Thu Jun 03, 2010 8:21 am
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