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2385 reconnect PS00 to P400 pin question

dankik said:
You probably should be testing from Pin 1 to Pin 2, then Pin 3 to Pin 2.
Both should be open since they go through the cap.
J737 looks OK.
On J737 it looks like C744 might be shorted.
Again, you should be testing J738 Pin 1 to Pin 2, then Pin 3 to Pin 2.
It should be open for both.

View attachment 3839903
Click to expand...
J737 Pin 1 to 2 = .82m Pin 2 to 3 = 26k Pin 1-3 = 1.4 m
J738 Pin 1 to 2 = 5.9k Pin 2 to 3 - 5.9k Pin 1 to 3 = 1.7ohms
Cap 744 reads 1.7 ohms OL uf
 
I was just testing transistors for a short and find Q720 and Q722 are shorted. I need to find replacements. This may be my issue
 
I'm not so sure that those account for the low resistance at J738.
Why all of a sudden do you have all of these issues with backward connectors, bad transistors, etc. when it was almost working a couple of weeks ago? What happened?
 
dankik said:
I'm not so sure that those account for the low resistance at J738.
Why all of a sudden do you have all of these issues with backward connectors, bad transistors, etc. when it was almost working a couple of weeks ago? What happened?
Click to expand...
I guess you didn't read post 1053. As far as backward connectors I could have made a mistake trying to see where the short was . As far as how it was wired , it has always been like that
 
Your right as far as low ohms on J738 , i removed both resistors and still when testing pins on J738 get the same results.
I retested those two transistors out of the board and still get short on diode test collector to emitter , then reverse probes same result.
I must still have a damaged component causing the readings on J738
 
Then someone besides you was in there before because those wire wrap connections are not factory and a sloppy job.
There is an outline of how the notch in the connector is to be inserted so you don't put it in backwards.
 
I also noticed when removing the two shorted transistors, Q712 was not original and was replaced, when it was reinstalled the solder on the collector and emitter had only a hairline between them, when moving the transistor the two shored out, i have removed the solder and re soldered, Also i found a few other that had new solder but no issues with possibly shorting, I now realize why when i tested Q712 and touched probe on collector it was enough movement to short.
 
This may mean something or nothing, Q766 Diode tests shorted both ways in the board
It tests good out of the board as per photo.
 

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It might mean that Q004 has a collector-emitter short. R788 is only 0.68 Ohms.
Disconnect Q004 and test out of circuit. Actually, it could be Q004, or Q006, or Q008 since the emitters and collectors are in parallel.

1789947907031.png
 
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dankik said:
It might mean that Q004 has a collector-emitter short. R788 is only 0.68 Ohms.
Disconnect Q004 and test out of circuit.

View attachment 3840615
Click to expand...
I am having an issue finding Q004, is that one of the main transistors in the huge heat sync? If so where are they marked for number.
OK i figured it out, they are the main output transistors. I pulled Q004 out and its shorted, I will order three new ones or should i replace all?
 
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sendust said:
Your right as far as low ohms on J738 , i removed both resistors and still when testing pins on J738 get the same results.
I retested those two transistors out of the board and still get short on diode test collector to emitter , then reverse probes same result.
I must still have a damaged component causing the readings on J738
Click to expand...

1790001304694.png
 
I replaced the shorted transistor Q004. And now pin 1 to 3 on J738 I get 16k. I was getting 1.7 ohms
I still haven't replaced q720 or q722.
On J737 pin 1 to 3 I get 640 k.
Do I still have an issue, or do I need to first replace the two missing transistors before measuring
 
For whatever reason, the L channel does not match the R channel (J738). from Pin 1-3 on the L channel (J737) you measured 1.4M, on R channel you measured 640k?
 
dankik said:
For whatever reason, the L channel does not match the R channel (J738). from Pin 1-3 on the L channel (J737) you measured 1.4M, on R channel you measured 640k?
Click to expand...
On the left channel I read 1.4m on pin 1 to pin 3 but I noticed if I wait it counts down to 640k. On right channel I read 1.7 ohms pin 1 to pin 3 but now after replacing Q004 it reads 16k but I still have Q 720 and Q722 missing untill I get replacements.
 
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