Audio issue a couple of weeks after Moreplay Upgrade [resolved]

[Paul Birkeland]

No, please don't randomly pull out all the transistors and attempt to replace them.  The odds that you destroy the board in the process of doing this go up with every transistor you pull.

Please do the shorts test I asked you to do and report the results, then also do the second test I posted. 

The diagnosis of the problem has to be completed before a remedy is attempted. 

 

[hmbscott]

Paul, just for clarity.

Can the shorts test be done with the transistor installed on the board?

 

[Paul Birkeland]

Yes, you should be doing that test with the transistors on the board.

 

[Doc B]

From a FAQ PB and I posted some time ago -

It takes some getting used to using meter probes in tight spots. Did you accidentally touched your meter probe to two terminals or leads at once? This can take out transistors. You can test transistors by unplugging the amp and measuring resistance across each of the three possible pairings of the three transistor leads. If any reading is very low, like under 100 ohms, the transistor is toast and will need to be replaced. It's usually the smaller 2N series transistors that fail.

 

[Galluch57]

Sorry that I missed the last several entries everyone. I did already remove all 6 transistors and replaced them. Same voltages at the test points.
6U - 173.3v
16U - 173v

B+ Reg TP - 177v

 

[Paul Birkeland]

Were any of the transistors that you replaced shorted out? 

 

[Paul Birkeland]

It's also possible that your main C4S board is working properly, but that there's a soldering issue related to the balance pot and the input/output wiring there, and the 6V6 grids are losing their ground reference and this is causing extremely screwy DC voltages.  I would evaluate this by temporarily soldering one bare wire across the L-Out, R-Out, and ground lugs next to the balance pot.  That will provide a DC short to ground, and if your voltages move dramatically, then you know the issues is in the input/balance pot wiring.

I won't be able to provide any more assistance on this until you complete this test. 

 

[Galluch57]

Is there  any chance you can provide a  diagram for this test? I’m not quite understanding .

 

[Paul Birkeland]

Temporarily soldering one bare wire across the L-Out, R-Out, and ground lugs next to the balance pot.

You are going to have to tell me what isn't clear about this instruction.

 

[Galluch57]

Voltages after soldering bare wire across L-In, L-Out and ground lugs next to balance pot:
6U - 172.3v
16U - 172.3v
B+ Reg TP = 175.4

 

[Galluch57]

Excuse the typo -- that should be:
L-Out
R-Out
Ground L
Ground R

 

[Galluch57]

I wanted to mention that it appears that 2 of the LED's light but two do not. Photo attached

 

[Galluch57]

When I completed the initial build these LED's did not illuminate but I read in the manual that some illuminate and some are dimmer, so since the voltage checks were within parameters when I completed the upgrade, I never thought much of it. Can you provide further troubleshooting advise?

 

[Paul Birkeland]

It would be helpful to go back to the plate loading resistors.  The white wires need to be slipped out of the front plate solder eyelets on the PC board, then connect each wire to one each of the removed 10K plate loading resistors.  Temporarily solder the other ends of those 10K resistors together and to a jumper wire, then run that jumper wire to Reg+ TP.  This will be kind of a hodge podge of wiring floating in the air, but it's useful to see if your plate voltages pull down to the correct value under these conditions.

 

[Galluch57]

I apologize - I’m trying to follow but it’s a bit confusing. I completely remove the two 10k resistors first?

 

[Paul Birkeland]

You already removed the 10K resistors in the process of installing the large C4S board. 

 

[Galluch57]

Understand now - the white wires you mention are soldered to the board at the ”Plate C” and “Plate B” locations?

 

[Paul Birkeland]

Yes, those are the soldered eyelets labeled as plate connections.

 

[Galluch57]

New voltage test:
6U - 90v
16U - 90.1v

Image attached (Please note that I used leftover wire from original Moreplay build so what’s going to Plate B eyelet was supposed to be white but I used red because I didn’t have enough white wire to make that connection)

 

[Paul Birkeland]

There's going to be a soldering issue or a failed component in the B/C area of that main green PC board.