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Yamaha CR-600 restoration advice

mbz said:
Pull F801,F803 and repeat measurement, still expect 1k
was it 1k from TR713 or TR715 and GND
edit D701,2 checked?
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1k from both TR713-ground and TR715-ground. Fuses removed gives me around 5k. I have zero voltage on cathode end of D702. Cathode end of D701 is giving me about 16V
 
Joolian said:
Ohms mode, got it. Right channel climbs up and maxes out pretty quickly, left channel stays around 1k ohms
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Do you have the L-channel output transistor mica insulators installed?
 
Joolian said:
Yes, they're new insulators and compound from when I replaced the original output transistors
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Hopefully a bit of solder or another metallic bit. Didn't get under the new insulator during installation. And poke a hole in the insulator.

This is something you might want to look into. ;)
 
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@Joolian my gut was telling me the power supply was ok. It seems you took it off the DBT and verified that today and more knowledgeable people are helping.

So you are seeing 1kΩ between the case (collector) and ground for both TR713 and TR715?
When you recapped the main amp board did you replace the other recommended components? FR701 / 702 are known to go out of spec for example.
 
The heat sink is connected to ground through the 2 long screws that hold it to the chassis. With the power off you could remove the screws and make sure the heat sink is not touching the chassis (pieces of cardboard under the corners). Then re-test the collectors of TR713 and TR715 to ground. If the 1kΩ path to ground is still there it is not through the heat sink. If is no longer there then the collectors are not insulated from the heat sink.
 
I'd be checking your final outputs NPN's and PNP's for proper placement while I was in there as well. That would blow both rail fuses if reversed.
 
avionic said:
I'd be checking your final outputs NPN's and PNP's for proper placement while I was in there as well. That would blow both rail fuses if reversed.
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Sure enough. It’s one of those things you swear you triple, quadruple checked and still had it wrong. Isolated the heat sink from the chassis, grounding issue persists. What I’m seeing now is an immediate 5k ohms of resistance on TR715, and 100 ohms on TR713 that very very slowly climbs up. I see the same thing when reading chassis to +\-BL where the wires come into the main board, for what it’s worth
 
Did you 6-way test the left channel output transistors when you took them out to reverse them?
 
rupes2 said:
Did you 6-way test the left channel output transistors when you took them out to reverse them?
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Yes, they’re still fine. I suppose it wouldn’t be a bad idea to just pull all of them and try and find a short on the back of the board?
 
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It sounds like the fuses saved your output transistors but it is likely some other components were taken out on the main amp board. Do any of the resistors show signs of overheating? FR701?
 
rupes2 said:
It sounds like the fuses saved your output transistors but it is likely some other components were taken out on the main amp board. Do any of the resistors show signs of overheating? FR701?
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Nothing’s sticking out to me. FR701 and R749 test fine.
 
I’ve been trying to follow traces and check resistance to ground of components along the way, the only thing I’ve found so far that looks odd is low resistance (~13ohms) on the emitter of TR705. Emitter of TR706 by comparison won’t even read anything within the range of my multimeter.
 
IMO failed outputs wont give you a low collector to GND resistance, more likely to be something physical like damaged mica. I like the idea of pulling the fuses when doing such measurements, to break the path through rectifier diodes and transformer secondary.

D701 at 16V is odd but is not in play for the -ve rail/resistance measurement

You could try measureing dc voltage at each TP1,2,3,4 to GND, this should rule out the outputs.
I'd be inclined to remove the outputs and connect any diode handy (1N4148, 1N400x,,,) between output b-e solder pads, alternatively pull the outputs then measure resistance between collect solder tabs and GND.
 
In addition to above double check:

Fr701 integrity
C723 integrity
With both removed, re-measure Tr705e to ground, if still a short, then you have a physical short somewhere nearby
 
mbz said:
IMO failed outputs wont give you a low collector to GND resistance, more likely to be something physical like damaged mica. I like the idea of pulling the fuses when doing such measurements, to break the path through rectifier diodes and transformer secondary.

D701 at 16V is odd but is not in play for the -ve rail/resistance measurement

You could try measureing dc voltage at each TP1,2,3,4 to GND, this should rule out the outputs.
I'd be inclined to remove the outputs and connect any diode handy (1N4148, 1N400x,,,) between output b-e solder pads, alternatively pull the outputs then measure resistance between collect solder tabs and GND.
Click to expand...
If I’m correct in understanding what you’re saying, I’ve checked ground resistance on each pad for TR713 and TR715, and emitter and base both test fine, it’s just the collector pad on each one where I see low resistance.
 
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