High voltage on terminal 1

[pdrm350]

I have scratchy/crackling sound issues with my Crack + speedball.  After the voltage check I found a high variable voltage (140~190 VDC) on the terminal 1, B1 and B4.  What could be the issues?  Thanks!

 

[Doc B]

Sounds like a loose connection.

 

[pdrm350]

Could a bad tube be cause of this issues?

 

[Paul Joppa]

Check the other voltages, especially the 12AU7 socket. Do the tube heaters glow? LEDs?

 

[pdrm350]

Terminal/Voltage(VDC)

1. 80~190
2. 180
3. 0
4. 184
5. 75
6. 0
7. 182
8. 0
9. 111
10. 0

A1 76
A2 0
A3 1.6
A4 0
A5 0
A6 182
A7 0
A8 1.6
A9 0

B1 80~190
B2 185
B3 180
B4 75
B5 185
B6 110
B7 0
B8 0

The LEDs in the the 12AU7 socket are lighting fine
The right side LED on the A board is blinking
The left side LED on the A board and the LEDs on the B board have a very low light. 

Thanks!

 

[pdrm350]

I haven't found any loose connection and the tubes heaters glow.

 

[Paul Birkeland]

This sure sounds like a loose connection, or a flaky solder joint.

 

[pdrm350]

Thanks everyone!

Are suspected in an area or part of the loose connection?  I've not found any  loose connection so far.  :-\

 

[Paul Birkeland]

You can try swapping the small boards right to left, if the voltage issue migrates to terminal 5, you have a flaky connection on the board.

If it doesn't move, you have a flaky connection at A8, A7, or A6, and the parts those connect to.

 

[pdrm350]

Will do.  Thanks for your help and guidance!

 

[pdrm350]

You can try swapping the small boards right to left, if the voltage issue migrates to terminal 5, you have a flaky connection on the board.

If it doesn't move, you have a flaky connection at A8, A7, or A6, and the parts those connect to.

I swapped the small boards. Here are the new voltages:

1. 79
2. 194
3. 0
4. 195
5. 75
6. 0

A1 80~100+
A2 0
A3 1.6
A4 0
A5 0
A6 79
A7 0
A8 1.6
A9 0

What do you think? Thanks!

 

[Paul Birkeland]

Since A1 is connected to terminal 5, can you see if the voltage is jumpy there also?

-PB

 

[pdrm350]

Since A1 is connected to terminal 5, can you see if the voltage is jumpy there also?

-PB

Yes, the voltage is jumpy.

Update: I removed the Speedball, now the Crack is working fine. 

It looks one of the TIP-50 transistors has a issues, the left side lead and the right side one have connectivity from both sides. I'm not sure if it's all the Speedball issues though. 

 

[Paul Birkeland]

The TIP-50 transistors are on the larger PC board, which seems to be OK.

I believe you may have a flaky solder joint on that small PC board that is now feeding terminal 5.

 

[pdrm350]

The TIP-50 transistors are on the larger PC board, which seems to be OK.

I believe you may have a flaky solder joint on that small PC board that is now feeding terminal 5.

Two of the LEDs on the larger board didn't have light.

I've checked the all the joint connections on the small boards, but Yes, the A board doesn't work as same as the B board.

 

[Paul Birkeland]

You haven't mentioned this until now, was it a problem when you first posted?

 

[pdrm350]

Honestly, I didn't check the LEDs on the large board at the beginning.

 

[pdrm350]

It sounds great even without Speedball.

 

[pdrm350]

Update: I found a same issues with 2N2907 transistor on the A board. 

Is it possible that the Speedball's issues are related to the TIP-50 and 2N2907 transistors?

 

[Grainger49]

The best way to check a solder joint is not to touch it.  If you are checking the final lead on the transistor that feeds the output of the C4S board check from the transistor lead to the terminal that the wire from the board ends up on.  This checks the transistor solder joint, the trace on the board, the solder joint on the output point of the board and the wire to the terminal in the amp.

The point is that if you check resistance on a bad solder joint you may be forcing it to read good when it is actually bad.