Voltage help on 2015 Crack Model

[johnnys]

Hey All,
I'm thinking I've got some cold solder joints, and I was hoping you could help me identify them. This is an April 2015 model Crack that I put together ages ago but am just now getting around to troubleshooting. All resistances check out and both tubes light up evenly when it powers on, no trouble with the fuse. The bottom LED lights, but the top LED running to A8 does not. One strange occurrence was that the 6080 tube did not light up the first time i powered up the amp, but after removing and replacing the tube it fired up just fine the next time. No idea if that means anything, was just curious.

Photos are attached, let me know if others would be helpful. Appreciate all the help here.

Voltages are as follows:
1. 153***
2. 170.9
3. 0.5
4. 170.9
5. 78.2
6. 0.3
7. 153***
8. 1.1
9. 105.4
10. 0.4
11. 74-60*** got different measurements two times
12. 0
13. 170.9
14. 0.1
15. 195.1
20. 0.3
21. 218.9

A1. 78
A2. 0.9
A4. 0.1
A5. 0.1
A6. 153***
A7. 0.7
A9. 0.1

B1. 153***
B2. 170.9
B3. 153***
B4. 77.6
B5. 170.8
B6. 105.1
B7. 0.1
B8. 0.1

Photos:

Thanks again,
John

 

[Paul Birkeland]

If these two diode leads touch, you'll have other problems.

Can you measure the DC voltage at A8?

-PB

 

[johnnys]

Thanks for your reply, Paul.

Yes, those diodes were touching, I’ve separated them at the point that you circled.

My DC voltage at A8 is 8.2.

 

[Paul Birkeland]

You have a damaged diode going to that terminal.  You can run a wire from A3 to A8 and your amp will likely work properly (and your voltages should fall into line).

-PB

 

[johnnys]

Roger that. I will get that done tonight. I'm assuming I should remove the damaged diode while I'm at it?

 

[Paul Birkeland]

You can leave it in if that's more convenient.  It has failed open.

 

[johnnys]

Alright, I bridged A3 to A8 with a wire. After turning the amp on to test the tubes the input tube flashed brightly 2-3 times. Now, only one side of the input tube glows and I believe both LED diodes are now blown as my multimeter diode tester now longer lights up the LED A3.

A3 and A8 now reading at 34.4 DC. Other anomalous readings coming in at about the same as before.

I actually have the speedball upgrade kit which I believe has 8 more of these diode LEDs. I can use those for the time being to replace these, but need to figure out what’s frying them.

Thanks again for the help.

 

[Deke609]

I'm thinking I've got some cold solder joints,

Hi John - I'd try redoing the solder joints at and around the PT. The 2 circled below look particularly suspect.

Good luck!