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Yamaha M-85, after recap not working, R221/222 get hot

S

Subwerk

New Member
Hi guys,

I recapped the amp, an inheritance of my father, because it was really a mess after a water damage. The dirty rainwater was more then a week within the amp. After a very long period of drying I never expect the devices work anymore - but it does! So I decided to recap and give him a new life. I also let frame sandblasting and powder-coating. It looks amazing - better then new.:)

Now the downside, it do not work anymore.:( For my apology I must say I did a lot of recapping in the past of other amps and all went well. I have the SM also the printed from a M80 and my Test-equipment is also fine, VOM, Hameg Scope, Component testers and a Variac is here.

I investigated now hours to find the issue but I stuck and now I need your kind support please.
I plugged the power to the variac and increased very slowly the voltage. From the beginning on I noticed the ampere meter of the variac increases also and I was immediately sure - something is wrong. Then, I saw at approx 20V the R221/222 get burnt and smoke. I changed the two and started again my test on the variac. At 10V on the variac, the both resistors get again hot, I'm sure, if I increase further, both will again blow away.

I de-soldered some devices like TR123/124, TR117/118, TR113/114 and the D119 and tested them with component tester - they are all ok. I measured a lot of resistors, most of them without de-soldering, also not issue could be found. I checked again and again all the changed devices, cables and measured the voltage inside the device. Also OK until now, no noticeable problems so far.

I need your support please, which part's I should now test next?
I tried to understand and read the schematic but despite I'm experienced within this kind of electronics, I'm not a professional and my good electronic knowledge to find the Issue is not enough it looks like.

Thank you for your support and advice in advance, Alex
 
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Did you get all the dried up glue around C162 & C163 remove and any of the corroded component leads cleaned or replaced ? Corroded jumper wires around the copper buss bars replaced ? Did C162 and 163 get installed correctly ?
 
If all you did is recap then it would seem most plausible a cap was installed backwards or maybe a solder bridge.

But, looks like you have the attention of an expert in the field of Yamaha amps.
 
Thx Avionic! :beerchug:
I remembered something else I did today, I removed one of the two R222 and R221 then I could increase the voltage on the variac without an issue to 200V , Relais clicked but then the remaining resistor get hot again and I must decrease voltage immediately. It did not matter which resistor of the both I removed or let stay in the device. After I putted the 2nd resistor back into the device - behavior is also as it was, 10V max then both resistors get hot.
 
What did you replace C164 with ?

Should be a 47µf/25v -- non-polar or bi-polar

The M-80 schematic shows a 100µf polar and the M-85 schematic shows a 47µf polar -- both are errors in the schematic..
 
Last edited:
avionic said:
Did you get all the dried up glue around C162 & C163 remove and any of the corroded component leads cleaned or replaced ? Corroded jumper wires around the copper buss bars replaced ? Did C162 and 163 get installed correctly ?
Click to expand...
Yes, I cleaned all very precise, will make a Foto tomorrow to show. The jumper wires l did nothing because they looked good, but I can double check. The copper bars I removed, cleaned them all and polished with Autosol. Directions of caps I checked every particular, look als fine. I have a M-80 also open beside the M-85 to compare because they are very similar. The M-80 have blown power transistors…I bought him defect.
 
The M-85 is and M-80 with all the service bulletins complied with --
 
avionic said:
What did you replace C164 with ?

Should be a 47µf/25v -- non-polar or bi-polar

The M-80 schematic shows a 100µf polar and the M-85 schematic shows a 47µf polar -- both are errors in the schematic..
Click to expand...
Hmm, let me check tomorrow. Great you’re responding so fast, really cool :)
 
Subwerk said:
Hmm, let me check tomorrow. Great you’re responding so fast, really cool :)
Click to expand...

For future considerations...

To that point, as has come up time and again, replacement with part like what's on the board is generally the right way to go rather than strictly by schematic values.
 
Subwerk said:
Hmm, let me check tomorrow. Great you’re responding so fast, really cool :)
Click to expand...
Hello, I checked the C164 and you was right, I had the wrong capacitor inside, it was a non-bipolar.:thumbsup: Now I changed to bipolar and tried again. Now I can increase the voltage on the Variac up to 80V…but unfortunately the same issue comes back :dunno:, both R221 and R222 get hot and begin to smoke. I stopped then immediately. My feeling say we’re very close to find the main issue/root cause… What do you suggest I can check now next?
 
A few more parts to check..
1. D111 thru 118 , D120 and D159

2.TR107 thru TR112
 
TR107,108,109,110,111,112 all ok
D120 and 159 ok
D118 ok, the rest I must check tomorrow.
I’m just wondering why both resistors getting hot…isn’t it the case each of them is for one channel…so I have an issue on both channels or a component which is working for both channels is the issue…hmmm…
I’ll inform you tomorrow about the other components…
 
Ok, I tested now D111,112,113,114,115,116,117,118 all ok. What should I check next?
About my “recap” I honestly must say that’s not the only thing Idid. I also changed the both VR to new ones and some Resistors because the aggressive glue eat some of them, used new wires and removed the old silicon pads on the power transistors and used thermal adhesive tape. I also changed some mica caps around the glued section with silver mica. All the same values of course. Maybe I changed too much? Hopefully not…
What do you suggest to check next in line?

Btw I really want to bring this puppy back to life, I will pay the one who helps me 100USD via PayPal. Nothing is for free and I would love very appreciate when we reach this together and can learn more to troubleshoot such errors. I know, the M-85 is not an easy one to start with…
 
avionic said:
What did you replace C164 with ?

Should be a 47µf/25v -- non-polar or bi-polar
Click to expand...

I believe that you can use a polarized cap, but the polarity marks on the board are backwards. C164 maintains a DC voltage. If you use a polarized cap, you must install with polarity opposite the marks on the board.

Make sure that the bias pots are setting the bias to minimum and not maximum. Check the bias voltage and confirm this when you turn the pots.

R221 and 222 feed supply to both channels, not one channel each. One is for positive supply, the other is for the negative supply. Don't try to run the amp with one or the other resistor removed.
whoaru99 said:
For future considerations...

To that point, as has come up time and again, replacement with part like what's on the board is generally the right way to go rather than strictly by schematic values.
Click to expand...
 
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