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2275 Phono Board P400 Left Channel Out

catrafter said:
Double check the wire wrap connections on J401 and J403.
Maybe something is shorting out when it's mounted. It should operate fine with the board loose.

Tom
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Thanks for your input, Tom. I've left the board loose, and have been checking the collector voltage on H405 each time I try something, and it's always 0.6V. The wire wraps on J401 and J403 seem OK, pic attached. I still re-flowed the solder on the solder side, just to be thorough.

20200426_112659_resized.jpg
 
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sanjib said:
At both sides of R432 with respect to the ground? Compare it also with R433 at both sides wrt ground.
Click to expand...


Voltages:
At the side closest to J404/J407:

R432: 33.6V
R433: 33.7V

At the far side:

R432: 0.6V
R433: 0.16.5V

Sounds like R432 is bad? It did read about the correct resistance, 3.3.
 
sanjib said:
Is the far side of R432 and ground chassis showing continuity?
Click to expand...

No, it does not show continuity to ground. I actually just pulled it out, figuring I would be replacing it, then had to reinstall it to test for continuity to ground.

EDIT: Just checked R433, far side shows no continuity to ground, either.
 
R432 should be 3.3K. I don't think that far side should show any continuity to ground. That side is connected to the collector of H405 and another side to the supply voltage pin J806 via R434.
 
R432 does measure 3.3K. Far side shows continuity to collector at H405. I don't see any supply voltage pin named J806. Typo? I will now pull R434 to test.
 
sanjib said:
Did you check H403 and H401? Are they good? Also, check R416 and R418
Click to expand...

I checked the transistors earlier - here are the collector voltages:


H404 6.0V
H403 1.7V

And the last two:
H402 1.9V
H401 2.3V

I did check R418. Will now check 416.
 
Just looked back at your voltages and saw that I missed your low collector voltage on H403. Have you replaced or tested that out of circuit? I think KSC1845 is a replacement. I would also be interested in R418.
 
I have KSC1815s for replacements on the 2SC458. OK for these too? Will check H403 now.

EDIT: H403 =2SC1344. Data sheet says min hFE is 250. This one reads 264. Good?
Typo corrected to 2SC258
 
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It seems like the circuit after R432 acting like it is open and you are not getting any voltage drop at H405 collector.
H405 and H406 are 2SC458 and I think all of the transistors in this board usually replaced by ksc1845
 
The KSC1815 were previously recommended here at AK by Avionic in a long ago thread, and I had some, so I used them. Thing is, one channel works, one doesn't, so perhaps it is a suitable substitute.
 
I think KSC1815 will work. If you find H401, 403, 405, and 407 good. As you already checked R416, 418 and 432, my guess the problem is somewhere in the resistors (R428, 426, 424) either anyone is open or problem in the solder joint.
 
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