Outer two LEDs on channel A C4S board not lighting up [resolved]

[amerk84]

I successfully installed the shunt regulator with no problems at all an all voltages within spec (first time I got something to work right away ).

Next I got to soldering and installing the two C4S circuits. At first all four LEDs on both the channel A and B C4S's did not light up. I started troubleshooting by first re-soldering only the joints that are part of the main circuit. This fixed the channel B C4S board as all four LEDs on that now light up. However, on the channel A C4S only the inner two LEDs light up. So I disconnected it from the main circuit, re-soldered all the connections, and then re-attached it to the main circuit board. Still only the two inner LEDs light up (I attached a photo of the channel A C4S).

Any ideas what my next step should be to troubleshoot, or what might be causing just the outer two LEDs to remain off?

-Andrew

[Doc B.]

What's the voltage at IB?

[amerk84]

The voltage at IB is: 108.5V

other voltages:

2 - 68.7V
18 - 79.6V
26 - 79.4V
31 - 107.3V

[Paul Birkeland]

What do you have at IA?

[amerk84]

IA: 108.5V

[Paul Birkeland]

You have basically no voltage drop across one C4S.  If both LED's are illuminated on the 9 pin socket under that board, then you have a short on that board (might be two legs of a transistor accidentally soldered together, or a jumper issue (not wiring IA to IB, but rather IA to OB or IB to OA). 

If one LED is off on the socket, then resolder all joints on that PCB.

[amerk84]

Both LED's on the socket light up. However, unlike the socket on the channel that's working where both LED's illuminate at the same time, the socket LED closest to 8 takes about 5 seconds longer than the LED by 4 before it gradually reaches the same brightness. Would this indicate anything specific that could be going wrong?

I checked for a shorts and there are none that I can see. I attached tope and bottom images of the PCB for reference.

[Paul Birkeland]

Try swapping the 6922's to be sure the problem doesn't follow a tube.

[amerk84]

You got it! That is the source of the problem. I switched the tubes and now all four LEDs on the right PCB light up and only two of the four LEDs light on the board that was previously working.

Paul, where can I get a new tube to replace the defective one?

[Doc B.]

Contact [email protected]

[amerk84]

Thanks for the help!