LED ON C4S

[M42]

I've installed the two C4S boards for the Integration upgrade, however one led on the B side output is not illuminating. The led is on the A side of the board. The diode directly below it burns extremely brightly compared to the others. The diodes on the sockets are lit and the shunt regulator is working within spec.

Voltages:

terminal 2    60.9v
terminal 18  92v
terminal 26  92v
terminal 31  61v

B Side CS4  1A  94.4v    1B    94.3v
A Side CS4  1A  108v      1B   108v

[Paul Birkeland]

The first step would be to reheat the solder joints on the middle legs of the MJE350 transistors.

If the diodes on the socket under the board in question are lit (especially I'd they are brighter than those on the socket of the working side), you need to inspect your soldering under the board to look for solder bridges between component legs.

[M42]

I'll reheat the legs on the transistors and check the board for solder bridges. The diodes on the sockets do burn with equal intensity, it's only the led below the "failed" diode that is burning very brightly. Thank you for your continued assistance!

[M42]

I neglected to mention a mistake I'd made when I first installed the C4S boards. I had not installed the two jumpers on the bottom of each board (and powered on the amp). I don't know if this would have any bearing on the problem. No more working too late trying to complete a project!

I've not yet had a chance to reheat the solder joints on the transistors and check for solder bridges. Hopefully I can complete this tonight and report back.

[M42]

I reheated the legs on the transistor, jumpers and wiring. I did find and remove a solder bridge on the A side PN2907 transistor. This resolved the issue with the diode not lighting. However, I seem to have created another issue. The led directly below this (that previously was so brightly lit) is now out. The diode on socket pin 3 is no longer lit!

I have checked the board very carefully and don't see anything else that might be of issue. I took more voltage readings:

Terminal   2    60.6v
              18    -.022v
              26    -.026v
              31     61v

OA    -.029v
1A     112v
OB      61v

[Paul Birkeland]

You may want to contact replacement parts. The PN2907 and MJE350 need to be replaced on that half of the board, or a new board needs to be constructed.

[M42]

Thanks for your help Paul, I will request the replacement parts. I'm curious did the solder bridge destroy both components?

[Paul Birkeland]

Thanks for your help Paul, I will request the replacement parts. I'm curious did the solder bridge destroy both components?

Possibly yes, possibly no.  It's safest to just replace both transistors.

-PB

[M42]

I have received and installed the replacement transistors. All the diodes are lit! The voltages read:

Terminal:

2   61.1v
18 62.2
26 62.0
31 61.7

The manual indicates values should be 65/90 v plus or minus. Somewhat on the low side, but within limits it appears. The solder bridge on the 2907 must have caused the fault. I'll blame my ageing eyes. Thanks Paul et al who took the time to assist!

[Paul Birkeland]

I'm glad you got it all sorted out. Those low voltages are indicative of high emission from the 6922's, which is a good thing.

-PB

[M42]

Thanks again for your help Paul. That's good news regarding the voltages, I have a new matched and balanced set of JJ 6JD8's in the preamp. I like them a lot.