Yamaha M-80 Help Needed...Again

[goatropercu]

I understand the importance of visual aids so here are a few pics.

Thank you.

 

[goatropercu]

Well boy do I feel like a big dummy. I was poking around with my meter and found a discrepancy between channels. Upon further inspection i found where the pcb had what I consider a fairly mild abrasion between R151 and connection #2. Big thanks to @bberkom and @avionic. I would have never have suspected this nick to break circuit. I'm not done, but the machine is out of protect on power up. More to come. Thank you all for your help. Dumpster dog may live.

Update: I took and attached a pic. The picture makes it look very obvious, for shame. I need to use the magnifying glass more often.

 

[avionic]

 

[merlynski]

Obiwan was on duty, the defect you saw wasn't the defect you were looking for . . .
Good you found it!

 

[avionic]

Good looking soldering . If that is yours.

 

[goatropercu]

Idle set to 15mv on both sides. Offset at acceptable (milli)voltages. This is good. Put it on scope with a signal, things seem to be looking up. Now we’re on the test speakers, hell yes.

This amp has been quite a trip. This thread doesnt cover a whole lot of previous hooplah. One thing is clear, i have a boat load of homework to do on oscillation, fets, etc, etc. I will certainly never trust a RCH of exposed copper again.

Much appreciation to everyone here who has the experience, knowledge, and kahones to lend a hand. One day i hope to be there.

 

[goatropercu]

Good looking soldering . If that is yours.

Some of it has to be, feels like i touched every pad on the left side and then some. I appreciate the positive attitude Dave. You da man.

 

[Semanon]

Keep us informed through the home stretch and your listening impressions.

 

[Asmodeus2112]

Great job sticking with it. That is one of the best feelings when you turn an amp on and the problem is gone and it nicely clicks out of protection.

 

[goatropercu]

Thanks for the encouraging words. I really felt like a goon after taking that picture, but the break is not nearly as apparent to my naked eye. Magnifying glass will now sit next to soldering iron. The amp has moved up to the dedicated garage speakers, so far so good.

Good lesson in sticking with it. I got another working M80 in the same deal. Fella literally plugged this one in saw smoke and dropped it in the roll off. It was tossed out then tossed in, cue rimshot. I’d be lying if i said i wasnt tempted to hide this amp away in the closet as a backup parts unit, especially once things got heated (on a roll here), but that’s not me. I like them to work, and always learn something in the process.

Lastly, i used to not be a fan of black boxes and red led’s, but the M80/85 have changed my outlook. I dig em.

Thank you all very much for your time and help.

 

[Semanon]

These are my constant companion at the bench.

 

[analog addict]

These are my caps companion at the bench.
View attachment 2259917

Heh, I have to use one all the time or I can't see $hit

 

[goatropercu]

Looks like a meter lamp is out. Not popping the cork just yet.

Problem solved. Now we’re cookin’.

I’m running it at a decent clip now. The left side seems to get a little warmer than the rt. Rechecked idle and offset, idle at 15mV on both channels.

Left ch offset at -15mV.

Right ch offset at 3mV.

 

[avionic]

The left side seems to get a little warmer than the rt.

Transformer heat...

 

[goatropercu]

Transformer heat...

That was my initial thought and what i will chalk it up to. Thank you for putting my mind at ease. I hit all switching and output transistors w the laser beam thermometer while running it at decent throttle. Fun stuff.

 

[goatropercu]

Now wishing i had a C-80/85

 

[avionic]

Looks like a meter lamp is out.

Which one ? The light ( LED) below the scale ? Press the RANGE button.

 

[goatropercu]

Which one ? The light ( LED) below the scale ? Press the RANGE button.

It was the bottom of the 3 middle lamps. I put a new 8v 150mA incandescent lamp in then took the pic. “Problem solved” would have likely been more appropriate than “now we’re cookin”. Sorry for the confusion there.

 

[avionic]

Oh..OK..

 

[goatropercu]

The amp played all day (a little over 8 hours straight) at a low to moderate listening level. Finally after quittin time i got to piddle with it. The meter level lamps are acting a bit odd. First thing i did was crank it up a notch to celebrate being one step closer to the weekend, the meters seemed to respond accordingly. Now i cant get the sons of guns to go back down. No signal but still indicating such. She’s warm, maybe heat related. I’ll take the face off, again, and clean the pots and switches, again, and look around for any foul play, again. I did not perform the meter adjustment procedure, everything looked hunky dory in terms of scope and local meters when applying a 1khz signal. Im using a phone as a preamp for testing, sometimes it seems the phone line out can cause a little trickeration. Will rinse and repeat.