Yamaha M-60 Score - Protection Mode Troubleshooting

kermit_xc

Active Member
picked up a M-60 in pretty freaking mint condition at Goodwill for $9.99 - but it doesn't leave protection mode ... so I started by removing C158 / C157 as I saw DSBG around, it actually looks pretty good underneath.

Output transistors job looks awful for factory job - but nothing stands out - quick visual inspection didn't reveal any obvious issues - so I figured I reach out here while I drive across the town to pickup some parts

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Closely inspect all the greenish resistors that are mounted up-right. These are a fuseable type of resistor. Look for a blackened band around there centers.If you find any. Check there resistance with a meter (isolated from circuit - unsolder one leg).

If you don't see any. Then we need to check for any DC voltage present at each amplifiers output.
 
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If component leads have any corrosion on them I replace the component. Jumper leads as well. For the copper bus bar. I remove it and polish out the corrosion.
 
Check the output transistors for shorts with a multi meter before bothering to do anything else. You can do this in circuit and it will right away tell you which channel is causing your issues. The last M-60 I rebuilt had the drivers and a bunch of small signal transistors blown but oddly the outputs were fine. If that's the case then the fuseable resistors are your next hint.
After that print out the amp section of the schematic and work your way back from the outputs and see what may have been damaged. I use different color highlighters to mark what I've tested and what is good and bad. That way you can pick up easily where you've left off. You're likely looking at outputs, drivers, some small signal stuff and however many of those fuseable resistors you find smoked. Maybe a diode or two as well.

Once you are done fixing whatever damage you find build a dim bulb tester and power it up using that. On power up the bulb should go bright and then dim quickly as the capacitors charge. If the relay doesn't click shut on a 100w bulb (this could take 30 seconds or so at the reduced voltage so be a bit patient) check for voltage at the relay pins that the amp feeds. If you've got more than a few mV then you've got more troubleshooting to do.
 
are you talking about the output transistors ?
No.. I was talking about measuring for DC voltage at the output of each amplifier circuit. If there is no DC then there is no reason to pull and check the output and driver transistors.
 
Gotcha, makes sense ... new caps are coming in few days, will check once their are in place. Stay tuned for the update ... and thanks for the guidance, we’ll make it sing again !!!
 
Closely inspect all the greenish resistors that are mounted up-right. These are a fuseable type of resistor. Look for a blackened band around there centers.If you find any. Check there resistance with a meter (isolated from circuit - unsolder one leg).

If you don't see any. Then we need to check for any DC voltage present at each amplifiers output.
 
Hey Black Knight, I have been reading all about the Yamaha M-60 Circuit Protection Issue,(since I am in the same boat!) I do not have any experience in repairing any stereo electronics. I would rather take it to a local reputable repair shop, but finding one is like finding a needle in a haystack! I am wondering if you could assist a Fellow Black Knight as well? Yes, I was stationed out on the West Side of Keflatraz as well!
Opie
 
Ah yes Rockville, if it weren't for the giant golf ball you'd swear you were on the moon. Nothing but rocks for miles and miles.

Craig
 
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