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Marantz 240 - bad transistor?

ocdecio

ocdecio

The proof of the restoring is in the listening.
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I am chasing a high DC voltage at the left amp board on a 240, so I am checking each of the listed transistors in the SM list. When I pulled Q508 (SJ2582) this is how the collector looks like:

upload_2021-1-28_13-0-30.png

Of course I will replace it, although the tester shows normal parameters and the DMM test passed as well.

I wanted to ask - has anyone seen this before, and I am concerned this may have implications to other components.
 
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goldswimmerb said:
I assume you've seen the 250 service bullitens? They apply to the 240 as well.
Click to expand...
Thank you for the reminder. Indeed, I applied two of them - the flyback diodes and the updated bias values (12-15mv). I will review the others and see if there is anything applicable to my 240 which is a later model.
 
From what I was taught, it is 'best practice' replace the bad component's complement as well.
Q503, 504
Q507, 508
Q510, 511

If one output is bad, you should replace all four (Q802,803.804, 805)
Q516 and 517 are AOS transistors and may not be that critical.

Tom
 
@catrafter thank you! I am most definitely replacing all of them, including Q516 and Q517 if no other reason that they are listed as possible causes for high DC at output. As for the output transistors, they seem OK but when I read the hFE they are all over the place, 3 above 100 and one at 48 (which the latter seems more appropriate). I don't know what could cause an output transistor to show a higher hFE but as someone said here, if it is out of spec it is not a good component.
 
@Steven Tate most definitely. I resolved the high DC voltage at output issue so now I will resume replacing them (since the issue that started it all is still there - after warming up left channel begins to hiss).
 
My list so far (for reference, my board is AW 115-1071 REV. NC ELI04)

Q501/Q502 - 2N5961 Mouser part 610-2N5961
Q504 - (SPS1951) - BC547 Digikey part BC547BTACT-ND
Q505 - (2N4125) - 2N3904 Mouser part 2368-2N3906-ND
Q506 - (2N4123) - 2N3904 Mouser part 512-2N3904TAR
Q507 - (SJ2582) - 2N5416 Mouser part 610-2N5416
Q508 - (SJ2582) - 2N3440 Mouser part 610-2N3440
Q517 - MPSA93 Mouser part 610-MPSA93
Zener diodes - 1N967B Mouser part 610-1N967BBK
Q802/Q804 - (SJ2520) - MJ21193G Mouser part 863-MJ21193G
Q803/Q805 - (SJ2519) - MJ21194G Mouser part 863-MJ21194G

Flyback diodes as per SM Bulletin - 1N

I pulled Q503 and read an hFE of 31.5k so this one definitely the Darlington (MPSA65) which I am ordering from Little Diode just in case. I put it back to get the amp going in the meantime.

Attached a spreadsheet with these items (rename to .xlsx)
 

Attachments

Just curious about Q505/506. The subs show the same number, but different Mouser part numbers. What is the difference in those two transistors?
 
Still having DC instability. Will try BC550C as diff pair, I replaced everything mentioned in the troubleshooting section of the SM.
 
Alright, DC instability was due to one of the 2N5961 either being defective or my soldering skills are not that great. Initially they read a beta of 428 both, and when I pulled them out one of them was reading anything from 284 to 308, the other 428 steady. Not a good sign.

Replaced both, bonded with their faces aligned to each other and now DC is stable again.

One thing I was doing wrong - I didn't let it warm up for at least half an hour before setting bias and DC, so I think bias was getting above safe levels after it warmed up. The SM doesn't say anything about adjusting bias with the unit warm, but I guess that would be "common sense" or "that's how these things are done" type of knowledge that I might be slowly getting to know. Would anyone please confirm that's usually the case?
 
This is why I ask about the correct procedure:

upload_2021-1-31_11-32-54.png

I thought bias was to be set cold. If it needs retouching after 30 minutes, wouldn't make more sense to say "wait 30 minutes and adjust bias"?
 
Two more substitutions:

Q510 (SJ2586) - MJE15030G
Q511 (SJ2585) - MJE15031G

Q510 (2N4123) - MPSA20

These were replaced in my attempt to figure out hiss/static/pops after warm up. I get bias and DC controlled, now need some burn in time to see if the current configuration holds.
 
In one channel I had a bad SJ2586 and I bought a pair of 2SC783/2SA483 from consolidated electronics to replace them. It is great to know that MJEs are good replacements. I was trying to put a complete list below.

Q501 2N5961 2N5961 Mouser part 610-2N5961
Q502 2N5961 2N5961 Mouser part 610-2N5961
Q503 MPSA65 MPSA65 Ceitron
Q504 SPS1951 BC547BTA Digikey part BC547BTACT-ND
Q505 2N4125 2N3906 Mouser part 610-2N3906
Q506 2N4123 2N3904 Mouser Part 512-2N3904TAR
Q507 S39613 2N5416 Mouser part 610-2N5416
Q508 SJ2582 2N3440 Mouser part 610-2N3440
Q510 SJ2586 2SC783 Ceitron/MJE1530
Q511 SJ2585 2SA483 Ceitron/MJE1531
Q516 MPSA43 MPSA43 Digikey part MPSA43-APMSCT-ND‎
Q517 MPSA93 MPSA93 Mouser part 610-MPSA93
Q518 MPS6519 MPS6519 Mouser part 610-MPS6519
Q519 SPS1928 2N5961 Mouser part 610-2N5961
Q520 2N4123 2N3904 Mouser Part 512-2N3904TAR
Q801 MJE180 MJE180G Mouser part 863-MJE180G
Q802 SJ2520 MJ21193G Mouser part 863-MJ21193G
Q803 SJ2519 MJ21194G Mouser part 863-MJ21194G
Q804 SJ2520 MJ21193G Mouser part 863-MJ21193G
Q805 SJ2519 MJ21194G Mouser part 863-MJ21194G
 
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@sanjib let me make sure the amp holds up with the MJEs. I also considered using MJE15032/MJE15033 because they are rated to double the voltage.

Also - I had to patch the collector on Q510 on the back with a wire connecting the two screw posts. I was somewhat uncomfortable making a change that I didn't read anything about anywhere but it looks like it worked.
 
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