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Yamaha M-80 Protection/Restoration

So it appears C+ is connected directly to B- which would explain the connection there. However, B- shouldn’t be connected to any other grounds without RY103 being closed. Does this mean my relay is stuck closed or am i reading the schematic wrong and that is it’s proper function without power.
 
This is a great power amp but please follow avionic.

Look around the big caps for glue corrosion.

Here is a pic with the caps removed to give you an idea. you will need to remove the glue and replace any affected parts, jumpers, ... I had both.

Don't forget DBT, mini grabbers, and common sense.

m80-cap-glue.jpg
 
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Yes, I will be removing the glue/replacing corroded parts once the replacements come in. Should be wednesday. In the meantime, I am tackling the speaker terminal replacement and noticed that issue i mentioned above. I believe this is the correct function as C are in series with B but do not know what speakers are turned on when looking at the schematic example to see what connections i should have.
 
I was attempting to diagnose the protection circuit by taking voltages, they were mostly all off. When i got to tr168 I wanted to check and make sure the emitter was grounded. So i went into ohms and pressed the base just to make sure it wasn’t grounded and click. Protection light turns off and the relay clicks. I take it off and it disengages. Same goes for when i touch the collector. click. But it’s not a solder joint as i pressed with a plastic tool and got no such result. I wasn’t aware my ohmmeter passes current but when the circuit is live i guess it does provide another path of follows. I assumed it was a bad transistor that’s getting funky when i’m ohming it, but I pulled and tested TR162-169 and they are all fine. I also replaced D166 and D146.

I have 37v at the collector of TR168 where is should be .3 and .005 at the base. So by grounding that 37v through my multimeter the circuit worked. So where is that 37v coming from, perhaps r205 is shorted?
Edit: R205 tested fine out of circuit

I also noticed i’m missing my 42v at the collector of TR167. I have it at the emitter and base but not collector.
 
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After studying the schematic i believe that with my meter i was turning on and off TR168 by either grounding the collector voltage or applying a small voltage from my dmm to the base voltage, allowing it to turn off/on and flow that same current to ground itself? This then lowers the voltage at the base of TR167 allowing the 42v to flow through engaging the relay?

So i have an issue somewhere before the the base of TR168 in the circuit?
 
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RyeGuy859 said:
When i got to tr168 I wanted to check and make sure the emitter was grounded. So i went into ohms and pressed the base just to make sure it wasn’t grounded and click. Protection light turns off and the relay clicks.
Click to expand...
Never use your multimeter ohm's function in and energized circuit.. Good way to blow a fuse or something else.
 
Got the old glue parts pulled in preparation for the new ones tomorrow, The only 1000uf tested and looked good, have replacements coming anyway. The 220uf Blackgates were pretty destroyed. One tested 50uF don't know esr. The other pulled a leg out as I removed it so it was probably open or destroyed anyway. Of the 330k resistors I couldn't get a good reading with the leads being rusted, the two diodes D119 and D120 measured okay but one of the leads snapped right off after I removed it. All those replacement parts should be in tomorrow. I'll pull those local 4 transistors and test them just to be safe. Hopefully those 220uf caps were the reason I was in protect.
 
Do you have any oxidized jumper wires along side that copper buss ?
 
No they were mostly untouched. One closest to the cap had a light amount on the surface but i was able to scrape it off/rubbing alc. I tested continuity along them front to back and it’s good.
 
When replacing HZ16L-3 16v zener, the originals are .5w. On hand I have 1w. I know the higher wattage changes the bias of the zener, but does the jump from .5-1w make a big enough change to make it a bad replacement? Or is this more of an issue on a jump from .5w to 5w?
 
So parts came in yesterday, just got them all in and the glue cleaned up. Still in protect. All voltages in the protection circuit are the same as before, so while the glue was bad it wasn’t the issue causing the protect.

I’ve attached a photo circled all the parts i’ve pulled and tested good. One notable thing is so am missing my base voltage at TR168 as I have 37v at the collector. Where should i look next? check more resistors in the protection circuit or is there a more likely place?
 

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RyeGuy859 said:
So parts came in yesterday, just got them all in and the glue cleaned up. Still in protect. All voltages in the protection circuit are the same as before, so while the glue was bad it wasn’t the issue causing the protect.

I’ve attached a photo circled all the parts i’ve pulled and tested good. One notable thing is so am missing my base voltage at TR168 as I have 37v at the collector. Where should i look next? check more resistors in the protection circuit or is there a more likely place?
Click to expand...
is R208 ok? It is the resistor between the collector of TR168 and the +LB line, which is ~+47V but is noted to be ~+42V at this point. What voltage do you get at the emitter of TR167?
 
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RyeGuy859 said:
So it appears C+ is connected directly to B- which would explain the connection there. However, B- shouldn’t be connected to any other grounds without RY103 being closed. Does this mean my relay is stuck closed or am i reading the schematic wrong and that is it’s proper function without power.
Click to expand...
Just curious. Did you replace any of the relays ?
RyeGuy859 said:
After studying the schematic i believe that with my meter i was turning on and off TR168 by either grounding the collector voltage or applying a small voltage from my dmm to the base voltage, allowing it to turn off/on and flow that same current to ground itself? This then lowers the voltage at the base of TR167 allowing the 42v to flow through engaging the relay?

So i have an issue somewhere before the the base of TR168 in the circuit?
Click to expand...
My next step would be to replace TR167 with a new part.

2SB560 > KSA916YTA

Or a KSA1220 if you can find one.
 
avionic said:
Just curious. Did you replace any of the relays ?
Click to expand...
No I did not, I believe my C relay may be a bit dirty as the resistance between the terminals changes when I would tap it. I know the A relay works as It engaged during my mishap earlier.


I have KSA916s currently. I'll drop one in and report. The original tested good when I pulled it before, so possibly not the issue.
 
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