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Samson Resolv 65a monitors - blown 220R 1/2w resistor again
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hymenoptera
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30th December 2012
Old 30th December 2012
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Samson Resolv 65a monitors - blown 220R 1/2w resistor again

Buddy of mine is sequencing and mixing on a pair of Samson Resolv 65a active monitors. Awhile back one of them stopped working. LED on front still comes on, just no sound from the woofer or tweeter.

I had him stop by and drop it off hoping it was something simple like a fuse, loose connection or cold solder joint. Once we opened it up it was clear there was an obvious burnt spot on the amplifier PCB where a resistor used to be.

Looking up the schematics at manual-archives.com I determined that the cooked componant (R9) was a 220 ohm 0.5w resistor and replaced it with the same. A nearby resistor (R7), a 1K 0.25, was scortched a little, so I replaced that one too even though it still showed 0.996 kOhm on the meter.

Reconnected everything and tested and R9 immediately got hot again. Saw/smelled smoke and killed the power.

Starting to suspect (Z1) 15v 0.5w zener and/or (Q21) C2061 power transistor. Hard to test either of these without peeling up all the yellow rubber they pour all over the PCB and desoldering each one by one. Groan, wtf is this rubbery stuff anyway?

SO, any advice for me or experience with fixing amps before I go and make things hard than they already are? I've gone and ordered more zeners and even some 2061 transistors to try and swap out. I have meters, irons, but only the most basic electronics skills, so all comments and questions welcome! Thanks.
hymenoptera
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31st December 2012
Old 31st December 2012
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I noticed the sister zener (Z2 on schem) looks like it might have gotten hot. It's buried under the tan glue the board is covered in, and the glue looks like it got hot there. Could be wrong.

Anybody want to take a peek at the amp schematic in the above link and postulate what might be causing R9 to burn up? Or what to test to try and narrow it down?

Thanks!
hymenoptera
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31st December 2012
Old 31st December 2012
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any advice on what's causing the voltage regulator to fail?

I have new 15v zeners ordered and on the way. gonna try to swap both out for new ones and see if that makes a difference.

is there a way to test them without desoldering them from the board?
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