Speedball troubleshooting [resolved]

[athomas21]

Hey there, I'm adding the speedball upgrade for the first time, and everything seems to be working except the bottom half of the big board.
The voltages are as follows:
Big board top half - B+: 178V
                               O: 99V
Big Board bottom half - B+: 195V
                                      O: 0V

Both of the LEDs on the top half light, but the bottom half LEDs do not light up. I've resoldered most of the joints on the bottom half and retried, and still the same voltage readings. I'm going to go ahead and resolder the entire board, but I just wanted to ask and see if there's a common problem that I'm not checking for in this scenario.
Also, everything else looks to be working well, all other LEDs light up, both tubes light up, and all other voltages are within spec. Let me know if there's any other information needed.

Thanks,
Alex

[athomas21]

Also, I went ahead and tested the TIP50 transistors, and for the top half board transistor all 3 resistance checks between the leads reads OL on my DMM, but for the bottom half board transistor I'm getting 110kΩ that steadily rises between leads 1 & 2, 392kΩ between leads 2 & 3, and 323kΩ between leads 1 & 3. Would this indicate that that transistor is blown/damaged?

[fullheadofnothing]

You have not  isolated the transistor from the heatsink. Improper use of the shoulder washer is the most common cause.

[athomas21]

You have not  isolated the transistor from the heatsink. Improper use of the shoulder washer is the most common cause.

Thank you for the quick reply and knowledge, I've taken off the hardware securing the bottom transistor to the heatsink and sure enough, the little black insulating washer's sleeve was not fully encasing the screw threads from the transistor.

Now that that's figured out, do I need to replace the transistor or is it probably OK? Also, would anyone know where I could get another of these insulating shoulder washers? The sleeve is pretty chewed up and I doubt I would be able to reliably install it without the same issue repeating.

[fullheadofnothing]

The transistor is probably fine.

You could re-install the hardware and test resistances as before to see if the re-positioned washer is doing its job before seeking a replacement.

[athomas21]

After reinstalling the washer and hardware, the resistance between each of the transistor leads and the screw was around 250MΩ, which I had thought to be good enough to work, but turning it on produced the same results with 0V at O and the bottom LEDs still not lighting up. I will see if I can get a new washer and update this thread when it's installed.

[athomas21]

After installing a new TIP50 and shoulder washer with the mounting hardware, all of the LEDs now light up and I'm getting voltage at O on the bottom of the large board. I rechecked all of my voltages, and all are still within spec except for O at the bottom of the large board, only now it has 180V. Also, when first turning on the unit, the LEDs for the the bottom of the large board light up almost immediately, while all of the other LEDs take about ~6 seconds to light up. Also, the 4 LEDs on the smaller boards are not nearly as bright as the LEDs on the large board.

What might I try next?

[Paul Birkeland]

Can you confirm that you get the correct voltage at "O" on the top half of the big board?

What voltages do you get on OA and OB on the small board?

[athomas21]

Here are the present voltages:
Small Board A: I = 181V
                        O = 71V
Small Board B: I = 181V
                        O = 81V
Large Board Top: B+ = 181V
                             O = 104V
Large Board Bottom: B+ = 183V
                                   O = 183V

[Paul Birkeland]

Just to confirm, you did run the stock amp without the Speedball and test it? 

I only ask because in this part of the circuit, the only real place you will find 180V is on pins 2/5 of the octal socket, and one side of each 47K resistor.

What voltage do you get at that "O" terminal with just the 12AU7 in the amplifier and no 6080?

[athomas21]

I built the stock Crack and checked all of the resistance and voltage checks, and then continued onto the Speedball without listening to the output first (my mistake).

Presently after removing only the 6080, the voltages are:
Big Board Top; O = 1.5V
Big Board Bottom; O = 203V
Small Board A; O = 71V
Small Board B; O = 80V

Also, the 2 LEDs at the Big Board Top do not light up with the 6080 removed.

Would you suggest I remove the Speedball, reinstall the 3kΩ cathode and 22.1kΩ plate load resistors and recheck all of the stock Crack voltages/resistances first?

[Paul Birkeland]

Can you go back and look at the wiring leaving terminals 7 and 9?

Getting high voltage at an "O" pad with no 6080 installed is very unlikely unless you have a miswire in the original build.

[athomas21]

Thank you for all of your help, patience, and prompt replies Paul, the unit is now working flawlessly thanks to you. I had stupidly installed a wire between terminal 9 and B+ for some reason, which was transferring over the high voltage from 2U to O on the bottom of the Big Board. Now all of the voltages are within spec, and the sound is absolutely divine. If you're ever in Portland, I owe you a beer.

Cheers,
Alex