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Old 9th July 2012, 08:29 PM   #1
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Default Could use a hand - Picking replacement output devices for Yamaha M-45

There was a mishap with a slipped meter probe and a bright blue flash, more about that in a minute...

I'm assuming that the output transistors are toasted; they are 2SC3182 and 2SA1265. A search on Mouser lead me to this pair of Fairchilds:



...which look like viable replacements. Are they good substitutes? Also, should I get the "O" or "R" version? (The hFE ratings are different between the two.) This amp is one of Yamaha's class AB/A where a switch on the faceplate biases the output devices into class A up to 10W, according to the literature. I don't know enough about circuit design to know if the Fairchilds will work in that situation. The schematic will be posted this evening, if need be.

So about the slipped probe, I shorted the "upstream" end of the emitter resistor to a jumper that ties into the corresponding transistor's collector. Most likely the drivers are toasted, too? I have yet to disassemble the amp and do any testing. The main 10 amp fuse blew right away. No semiconductors have burn marks - the board has a black mark; the resistor's lead and the jumper both have divots from the short.

Last edited by geaugafletcher; 10th July 2012 at 04:56 AM.
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Old 10th July 2012, 04:55 AM   #2
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Datasheets for the originals:


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