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Yamaha M-80 Protection/Restoration

Look over this portion of the main board for cracked solder connections, cracked traces, broken solder pads or solder bridging.

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Swapped TR168 with KSC2383. Also went over all the solder joints in the area for cracks and have no change in the voltages. Still in protect. I’ve also gone over all outputs/drivers on the heat sink to be sure there’s no cracks there either.
 
Make sure that the three main board hold down screws are tight. 3 out of the 4 secure the main board to chassis ground.
 
I tightened all 3 screws that attach to copper pads.

Remind you this is on a dbt with a 200w bulb.

37.94v 36.3v(TR168 side) R208 Voltage drop of .006v

36.33v(TR168 side) 36.36v R213 Voltage drop of .016v



Thought i was onto something as i found more solder joints under there foam but after removing the foam and resoldering them nothing changed.
 

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The fact that you keep finding poor solder joints is not good news, you have to reflow ALL solder joints, every darn single one, there’s simply no other way.
 
Just finished touching up every joint on the main amp board and the two power boards on top. Still no change.
 
I added the voltage before the diode as well.
 

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Okay thanks. The voltage before the diode seems low, what do you measure on the collector of Tr143 (PC limiter circuit)? My miserable schematic says ≈9.7V.
 
Tr143c is way off, also b-e voltage is low, the transistor is off. Is the solder work okay? Is C171 healthy?
Emitter and base voltages are somewhat high, may or may not be an issue (probably not). I’d take voltage measurements of all that section, bias current detector, etc. included, to have a voltage map of what’s going on.

If Tr143c is disconnected from the D146(?) it’s feeding, what happens, does Tr143c voltage change?
 
Solder looks good, C171 measures 10uf (in circuit)

With D146 removed I have 3.1v at the collector of TR143. Here are some other voltages in the area. I can make a broader map if that helps more.
 

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So the Emitter of TR143 is connected directly to HB+. Then my Base voltage is to high? That is fed off TR145/146 in each channel?

Still learning what feeds what/how the voltage flows so correct me if i’m wrong.
 
RyeGuy859 said:
So the Emitter of TR143 is connected directly to HB+. Then my Base voltage is to high?
Click to expand...
It’s a PNP transistor, so Vb = Ve + 0.6, in this case that’d be ≈86.1V . Unless that’s by design which at this point I’m not sure … following this schematic is a nightmare

Just looking for anomalies, none of this may matter, however.
 
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