Noise, Heat, and Sparks: Oh My!

[MrPotatoSalad]

There's a red jumper that goes from B+ to B+ on the big Speedball board.  Yank that, then remeasure B2/B5.

Same LEDs still lit. Voltage B2/B5: 71V

[MrPotatoSalad]

Should I replace the remaining two transistors on the top main board or do you have any other tests?

I've checked over every circuit on the boards and everything is in place. The only issue is that there has to be a bad part that needs to be replaced.

I could also try removing the smaller or larger boards and replacing them with their corresponding resistors if that would help eliminate extra variables.

What is the next step?

[Paul Birkeland]

Running the amp without the 6080 and just the 12AU7 will allow you to test the functionality of the front two boards.  Seeing 150+V at T2/T4 and something around 70-90V on T1 and T5 means that your small boards are good.

-PB

[MrPotatoSalad]

6080 out gives:
1:80
2:230
4:229
5:77

[Paul Birkeland]

Yeah, this is indicative of a short on the large Speedball board. 

You can put the 6080 back in, then try removing one of the "O" wires and running the amp.

Then try putting that "O" wire back and removing the other.

Let me know what you find.

-PB

[MrPotatoSalad]

Top O out:
1:68
2:70
4:70
5:21
LEDs same

Bottom O out:
1:83
2:204
4:204
5:78
All LEDs on except the bottom main board LEDs are out and top LEDs are bright.


Also, both LEDs on the 12AU7 socket went on with the 6080 out. All board LEDs were out.

[Paul Birkeland]

Top O out:
1:68
2:70
4:70
5:21
LEDs same

That's the problem area.

Bottom O out:
1:83
2:204
4:204
5:78
All LEDs on except the bottom main board LEDs are out and top LEDs are bright.

That side is good.

Also, both LEDs on the 12AU7 socket went on with the 6080 out. All board LEDs were out.

The LED's on the small PC boards should've been lit up pretty brightly with the 6080 out.  The LED's on the socket couldn't light unless this was the case.

-PB

[MrPotatoSalad]

The LED's on the small PC boards should've been lit up pretty brightly with the 6080 out.  The LED's on the socket couldn't light unless this was the case.

You are correct, they just weren't noticeable with my lights.

Should I replace both transistors on top then?

[Paul Birkeland]

I would go over that big board with a fine toothed comb.  You have one side that is doing what it should, and one side that isn't.  The most probable cause at this point is that two legs of a transistor on that side of the big PCB are soldered together.

-PB

[MrPotatoSalad]

I would go over that big board with a fine toothed comb.  You have one side that is doing what it should, and one side that isn't.  The most probable cause at this point is that two legs of a transistor on that side of the big PCB are soldered together.

-PB

No visible connection or measured connecection with any of the transistor legs. Perhaps the TIP50 or 2N2222 is bad?

[Paul Birkeland]

Yeah, I suppose swapping them both out won't hurt anything.

-PB

[MrPotatoSalad]

Replaced the top transistors and started it up. All LEDs were lit except the one at terminal 3. The bottom main board was strong. The top was very faint along with the small boards. The top may have been lighting the whole time, but it was so dim that I never noticed (had to turn off all lights. Started voltage check and it was in the 68V area for the first 2 terminals so I turned it off.

[MrPotatoSalad]

Resistance check on bottom TIP50 (black/red probe):
E/C:15M
E/B:15M
C/B:81K

Top TIP50:
E/C:infinite
E/B:15M
C/B:13M decreasing to 4M and now rising

Brand new TIP50 out of circuit:
E/C:infinite
E/B:16M
C/B:13M

When I removed the lower TIP50 because I was going to replace everything (but only did the top instead) the lower TIP50 measured then same as the new, so I didn't replace it. It seems that something in the board is causing a short.

[Paul Birkeland]

Yeah, a less fuzzy photo of the bottom of the board might reveal something.

-PB

[MrPotatoSalad]

I can't do any better. Only have a camera phone and a webcam. Webcam will do even worse.

I checked over all the joints. Everything matched the pictures in the instructions. The only thing noteworthy is that I initially installed the TIP50/heatsinks on the wrong side. When I took them out, the heatsink on the bottom of the board's inner joint (the one more towards the center) had the metal ring inside the hole come out. I scraped off the surface to get to the metal path and then soldered the heatsinks on the correct side. When I test for connectivity between the heatsink metal lugs, each one has connectivity to the other 3.

(You can kind of thee the bottom left heatsink joint extends on the board a bit to connect to the path.)