Speedball issue

[mteresko]

I completed the Crack assembly last night, and all was working well. I went on to the Speedball, and I've run into issues with the small board. OB measures 156.7v, the other voltage tests are all normal. Also, the LED to A8 is not lighting, and all the other LEDs are lit. I've reflowed all points on the board, checked continuity between the pcb and the chassis, double checked the orientation of the transistors, and tried a different 12AU7. Suggestions?

OA  76V
IA   171V
B-A/B  0V
IB   171V
OB   157V

[Paul Birkeland]

If the solder joint at A4/5 is not super solid, only one half of the 12AU7 will light up and you will get these exact symptoms.  If the center leg of the MJE350 on that side of the small PC board isn't really well heated, you will also end up with these issues. 

If you have reheated the solder joints for your LEDs and you now have 12V DC on pin 8, then you need to replace the LED in that position.  Typically this will only happen from applying too much heat to those solder joints.

[mteresko]

If the solder joint at A4/5 is not super solid, only one half of the 12AU7 will light up and you will get these exact symptoms.  If the center leg of the MJE350 on that side of the small PC board isn't really well heated, you will also end up with these issues. 

If you have reheated the solder joints for your LEDs and you now have 12V DC on pin 8, then you need to replace the LED in that position.  Typically this will only happen from applying too much heat to those solder joints.

A4/5 is good. Both sides light up, and were working prior to the Speedball.

I've reflowed the center leg of the MJE350 twice, and it looks fine. I've got continuity between B1 and the center leg itself between the board and the body.

I've reflowed A8, A3, and the center pin, and the A8 LED still won't light. I've got 14.2V at A8 and 1.6V at A3. Still 150V +/-  at OA. Now, both LEDs were lit and the amp was functioning normally prior to the Speedball installation, and I don't believe I did anything that would cause one to fail, certainly not reheating anything connected to it.

Time to try a new LED?

Thanks,
Mike

[Doc B.]

Many pads on the A side of the board need more solder. Add enough to give them a decent fillet and make them look more like the joints on the B side.

[mteresko]

Many pads on the A side of the board need more solder. Add enough to give them a decent fillet and make them look more like the joints on the B side.

Done, no change.

I tried switching the two diodes so the unlit one went to A3 and the working one went to A8, unfortunately I ham-fistedly broke the lead on the working LED. The non-working diode is now attached to A3 and there's nothing from A8 to ground, and OA and OB now are both around 150V. This seems to me to indicate that the original A8 diode has failed for whatever reason. And I now need 2 diodes! Any idea what may have caused the one to have failed? I don't believe overheating to be an issue as it was working, and no heat was applied after that.

[Paul Birkeland]

The LED going to A8 needs to be replaced.