Need Help - Yamaha M80/M85, smoked resistor

JonAnders

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I just finished replacement of the electrolytic capacitors in one of my two (yes, two) Yamaha M-85 amplifiers. Installed a fine bunch of Nichicon KYB, Muse, and Fine Gold. During this procedure I also removed the dreaded Sony bonding glue. I also replaced a zener (D119) which appeared questionable due to possible corrosion from the glue.

At final inspection, I was pleased with the capacitor solder joints. I was not so happy with the D119 solder joints, but they refused to look much prettier after a few attempts at touch-up. In hindsight (always 20/20), I should have desoldered completely, cleaned, and done fresh. But I didn't.

I connected the M85 with master volumes set at minimum. I powered up. All was good, and I heard the speaker relay click as expected. I then increased masters slightly and heard good music. Followed by a crackle. Followed by a puff of smoke. I immediately powered down - and I think I heard (hope I did) music still coming from both channels as power was switched off.

It appears R125 may have baked. That is the area served by the zener D119.

While I can solder quite well and have successfully completed a number of high-parts-count kits, I am not a techie with troubleshooting skills.

I welcome any and all input on the matter of how I might determine what other parts may have been damaged and how I may reasonably easily diagnose. Bear in mind I have my second M85, untouched, and fully operational to compare against. I do also have a variac and nice DMM.

I have done some searching and found some posts that might suggest R125 gave up the ghost and saved other components. But I don't know.

Help?
 

laatsch55

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#2
Member Avionic is a Yamaha guru, if he doesn't answer this thread, PM him...Joe may also chime in...
 

JonAnders

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I posted to one other site. But only to one forum here.
My apologies if I have violated some rule.
I will correct upon receipt of appropriate enlightenment. ;)
 

laatsch55

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No, no, no....you have violated no decorum here bud. Avionic hangs at AK and if you haven't posted there you might. Might get a quicker response out of him there...
 

stuwee

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Hello Jon, you didn't violate any rules here, you have a wealth of very talented techs here. Some more familiar with Yamaha than others, you will hear from them soon. Welcome to Phoenix!
 

JonAnders

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Thank you, all, for the very kind reception. I am very eager to get this issue resolved. Then I will begin recap on the second M85. It's a bigger mess than the first with respect to the Sony glue - globbed liberally everplace. Not really looking forward to it. But I cannot wait to hear them both working in tandem again. I drive each of my bi-wireable DQ20s with one amp each. Left powers woofer, right powers mid/tweet. Gives you all you need in Auto-A mode. No L/R channel crosstalk possible once the signal leaves the back of my Adcom preamp. Very sweet. Also upgraded op amp in the Adcom to LME79860. Cannot wait to hear improvements after replacing 25 year-old caps in all three units.
 

laatsch55

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When you want to hear A REALLY GOOD SOUNDING AMP, find somebody with WOPL ( White Oaked Phase Linear) and check em out...granted the Yamaha's are some fine amps....
 

stuwee

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Hey Jon, I had the MX-800U, which is an upgraded version of the M85, wicked nice amp, drove my old Martin Logan Sequels to amazing levels, rated down to 1ohm. You have 2 M85's for the Daul's, I suggest you see what the Yammie guys say since you seem to be handy on fixing these amps. I have to admit tho...I'm about to get into the WOPL club for my Summits!! Absolute power corrupts and absolute clean power corrupts absolutely!!
 

JonAnders

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I did briefly search and review some WOPL-related posts. Now the challenge is where to find them for audition? Now see what you have done? Yet another new entry on my never-ending to-do list!

I suppose my M85s would be ripe for sale after the recap/cleanup... perhaps money well spent in WOPL land.

Truth is, I would probably first move to another preamp. My GFP-555, while it sounds quite good, I do hear a bit of harshness sometimes that I think does not belong. Not sure if moving to the LM79860 will remedy that. The challenge - lamented by others in various posts - is the relative lack of good and reasonably priced preamps these days.
 
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WOPL Sniffer

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Jon, where are you located? The Happy Camper WOPL Club has members from one end of the country to the other. Auditioning is available. Too much fun.

Welcome aboard and good luck on the yammie... I love the big Yamaha amps too.

Perry
 

Fishoz

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Welcome to our little world Jon. Guarantied to spark your interest.

Where ya from? Maybe you're nearby someone that has a WOPL. I'm sure anyone here would love for you to have a listen.
 

JonAnders

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That would be counting my chickens prematurely. Still hoping for the arrival of a Yamaha guru to offer some guidance. I will probably start some in-circuit test measurements tomorrow if no word from guru. Perhaps comparison to working unit will offer enlightenment.
 

JonAnders

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#16
Just did a few in-circuit measurements should any guru appear on scene.



TR137, TR135 (on main board, on side/channel of main board as D119 and black smoke) which each show approx 52 ohms across one pair of leads (whether 1 and 2 or 2 and 3) and short across the other pair of leads.


TR137, TR135 (on main board, near rear of unit, on side/channel of main board as D119 and black smoke) which each show approx 52 ohms across one pair of leads (whether 1 and 2 or 2 and 3) and short across the other pair of leads. Not good. But could be worse. The Avionic-recommended replacements (2SA1494) are on their way (Digikey).
 
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orange

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Welcome Jon! Once you get a WOPL, you'll forget about those Yammies LMAO!!!
I still need to fix my CA-1000 and I've been watching a CT-800...

and I still have the T-480 tuner I got from Larry, it's running in the bedroom as the matching tuner to my 1982 Sony AV (two channel) integrated has a buzz...relay maybe?

The rears are ably powered by a Pioneer SX-400, but the SA-520 Jer fixed for me will get worked in!
 

nakdoc

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When an M85 burns small parts it is the tip of the iceberg. I would not recommend you try to repair this yourself. Let's see if we can find someplace near you to get it running again. typically a blown M85 will open several of the 4.7 ohm fuse resistors mounted vertically near the output transistors.
 

stuwee

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When an M85 burns small parts it is the tip of the iceberg. I would not recommend you try to repair this yourself. Let's see if we can find someplace near you to get it running again. typically a blown M85 will open several of the 4.7 ohm fuse resistors mounted vertically near the output transistors.
Jon, these are very wise words!! Nice to hear from you nakdoc!!
 
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