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M80 acquisition -

ha1156w

ha1156w

Active Member
Hey folks, I've acquired an M80 via a local pawn shop for cheap ($5!!) as "untested". I powered it up with a proper preamp and it immediately turns on the "protect" lamp. I understand they are also the recipient of multiple updates from Yamaha effectively creating an M85. Can anyone point me to the service bulletins
 
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Pop the hood and look for burnt components.Especially look around the two 1000uf 100v green nichicon "KS" caps. for real bad corrosion caused by dried up glue.
 
Check the resistance between the collector and emitter of all the output transistors mounted on the lower portion of the heatsinks.
 
Look for DC on the Emitters of the Outputs

ha1156w said:
Hey folks, I've acquired an M80 via a local pawn shop for cheap ($5!!) as "untested". I powered it up with a proper preamp and it immediately turns on the "protect" lamp. I understand they are also the recipient of multiple updates from Yamaha effectively creating an M85. Can anyone point me to the service bulletins
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Everyone has given you good advice, especially the glue comment which has plagued a number of mfg's for years yet they never stopped using the stuff. Checking the emitters for DC will at least identify which channel is shorted. I have all the service bulletins. That said, the M8x amps where challenging to work on when a set of outputs shorted.
 
AV Svc Labs said:
Everyone has given you good advice, especially the glue comment which has plagued a number of mfg's for years yet they never stopped using the stuff. Checking the emitters for DC will at least identify which channel is shorted. I have all the service bulletins. That said, the M8x amps where challenging to work on when a set of outputs shorted.
Click to expand...

Yes they are.When outputs go bad they tend to take out a handful of other parts as well.Its not pretty..:yes:
 
the-real-mandak said:
Hey gues... Give the M-8x some slack... If you have to go... why not with a boom and some smoke? Rock & Roll :D
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Which is one thing the mods do, prevent catastrophic parts failure upstream.

Chuck, we've seen only one SB mod (TSB66H) a recent AK member found posted on the M-80 amps. Can you perchance pass them along? I would like very much to extend the life of the one remaining M-80 I have here should an output let go in it.

P.S. I updated the M-80 schematic with TSB66H, I should post it for the AK database. Any wants a copy, PM me with your e-mail addy.
 
Have you given enough time for the Protection light to turn off? The Yamaha M and MX series amps always have the protection light on when first powered on. They turn off after about 5-10 seconds.
 
That's what I thought. I just got recently a damaged Yamaha M-70 and managed to fix it. Without the manual I didn't know how this amp operates.

So I turned it on, Protection went on and R966 went in flames (220R - flame proofed resistor, on the pre-drive board) since the previous owner didn't reassemble the heatsink support bar (the metal that holds the pre-drive board in place). What happened was, this metal bar scratched the pcb and made contact on the ground, feeding voltage where ever it went and fried R966, lol.

I checked everything and replaced R966 and went thru all the necessary checks stated on the service manual and everything is fine. And yes, Protection lamp does turn off around 5-10secs.

However...when I set the DC offset to 0V, it seems to move around 3mV to -3mV, back and forth. To those guys who has done this before, is this normal for this amp?
 
Anyone that receives the schematic with TSB66H mods from me, please proof it against the included mod to make sure I did it right. I haven't applied those mods to my M-80 yet.
 
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