Marantz 2215 - Lost left channel in FM stereo after re-cap

[bdondo]

I've been refurbishing a Marantz 2215 and just re-capped the MPX stereo decoding board (P400). Before recapping this board, everything worked fine. After re-capping, I no longer get output in the left channel in FM stereo mode. I get output in both channels when in mono mode. In aux mode I get stereo in both channels. The stereo lamp turns on in FM when the mono button is not engaged and turns off when the mono button is engaged.

When this issue first happened, I inspected the board and found C401 in backwards. I corrected that, but the issue remains (and I don't see how it would cause this). I also bumped the R428 trim pot when I was soldering, but put it back to pretty close to where it was based on the white paint that was on it. I verified that it still works in general and tried setting it to various positions to see if it would help -- no change.

I measured DC voltages at several transistors (the odd numbers go to the right (working) channel):

H406
B  7.9
C 16.7
E 16.7

H407
B  1.0
C 15.9
E  0.5

H408
B 16.7
C 16.7
E 16.7

H409
B 15.9
C  3.2
E 16.5

H410
B  4.8
C 16.8
E  4.3

H411
B  4.8
C 16.7
E  4.2

There's obviously something not right with the voltages at H406 and H408, but I'm having trouble tracking down the cause. I've also done the following:

• Checked for shorts in various places
• Removed and tested H406 and H408 - both have >200 hFe
• For the following, I removed them from the circuit to test:
  • Verified C413
  • Verified C416
  • Verified R437
  • Verified R431
  • Verified H414-H417 diodes
• J408: Can measure 100-300mV AC with DMM
• J407: 0.00mV AC with DMM
  • J407 has AC voltage when switched to mono, but it’s less than J408

The 2215 service manual doesn't list any DC voltages in the schematic, but I used the 2220 service manual to get an idea of what I should be seeing. In addition to the H406 and H408 voltages being off, the collector voltage at H409 seems like it could be a bit low compared to the 2220 expected voltages.

I've added my voltage readings to this part of the schematic:

Any ideas?

 

[MBuras]

Did you take note of this capacitor error on the board?

Marantz 2215
Tuner MPX board P400
Capacitor C414, 33uf, 6.3V (service manual lists it as a 10V)

BOTH the silk screen on the board AND the service manual board image are wrong.
Positive (+) is towards the inside of the board.

 

[bdondo]

Did you take note of this capacitor error on the board?

Yeah, I luckily noticed that when replacing the capacitor. I have it in correctly, and used a 25V version. I also used 25V caps for all the 10uF/16V caps in the schematic (the board actually had 25V caps installed anyway).

 

[bdondo]

It's baffling to me that the H408 has 16.7V at B, C, and E, and there's no drop across R437. Yet the transistor tested ok out-of-circuit in one of those cheap component testers. When something is this baffling to me, I assume it's probably a simple thing I'm overlooking

 

[bdondo]

P.s., I have an oscilloscope but don't have an RF generator. My scope has a function generator that goes to 25MHz or something like that. Not sure if those would help here.

 

[kwayde]

It's baffling to me that the H408 has 16.7V at B, C, and E, and there's no drop across R437. Yet the transistor tested ok out-of-circuit in one of those cheap component testers. When something is this baffling to me, I assume it's probably a simple thing I'm overlooking

If I measured those voltages on that transistor I'd replace it even if the tester said it was good. There have been a few times I replaced transistors with new ones that measured good on the Peak DCA55 only to find they didn't work in circuit. Pulled them and replaced them with others to have it now work.

https://docs.google.com/spreadsheets/d/1rccXRHhV_1d_m1VrNq0r4fU_jiuTM82X/edit#gid=560669483

 

[bdondo]

Thanks.. yeah, I was thinking the same thing and am now digging up KSC1845FTA and KSA992 transistors which I think should work.

 

[bdondo]

Swapping out H406 and H408 dropped the voltage at H406's base from 7.9 to 5.5V, and now the stereo light turns on, so maybe that's progress. Otherwise nothing else changed (still zero sound in left channel). Maybe I'll swap out a couple more transistors to see if it helps.

 

[bdondo]

Swapped H407 and H409 with new transistors and no change.

 

[bdondo]

Success! Well... even though I had the C414 capacitor oriented correctly, I also had the positive end shorted to the V+ side of R424, which is in the right channel. By the looks of my soldering, I "intentionally" bent the capacitor lead over to the R424 lead. When looking at the board from an angle, it sorta looks like it's supposed to be that way. It's kinda surprising this thing worked at all. The V+ voltage is now around 29V instead of 16V as well.