High Voltages At Small Board [resolved]

[Kaitlineddy]

Hello! I'm getting high voltages at the small board of the Speedball installation. I have not installed the large board yet.
The Crack had the correct voltages on its initial build. It has been working flawlessly for a few months in its original state.

- Red lights on 9 pin socket are not lighting.
- Both tubes glow.

Readings (with small board installed):
12U to:
    OA: 149
    1A: 159
    B-AB: 0
    1B: 159
    OB: 148

    1: 148
    2: 159
    3: 0
    4: 159
    5: 148
    6: 0
    7: 146
    8: 0
    9: 146
    10: 0

    R1A: 235 ohms
    R1B: 235 ohms

I tried reflowing the solder joints on the small board, but got the same readings.

Thanks in advance!! 

ps: If you need photos, I'll be glad to post them. For some reason they aren't uploading with this original post.

 

[Paul Birkeland]

I would definitely post some photos.  You may need to shrink them a little bit in order to be uploaded.

Generally what you are experiencing would be consistent with insufficiently flowed joints on the MJE350 transistors.  You can hold your iron on each leg of each MJE-350, then count to 5, then take the iron off and move to the next leg.

 

[Kaitlineddy]

Thank you for your quick reply, Paul! I've attached photos.

 

[Deke609]

Did you try this?

  You can hold your iron on each leg of each MJE-350, then count to 5, then take the iron off and move to the next leg.

cheers, Derek

 

[Paul Birkeland]

I would reheat the joints on the small PC board.  I think you have plenty of solder on there, I'm just not convinced that the joints are well flowed out. 

 

[Kaitlineddy]

I did reheat the MJE-350s' joints before those photos were taken, but I will try it again.
Will report back. Thank you!

 

[Paul Birkeland]

It is also completely possible that a prior build issue is just now surfacing after installation of the Speedball.  What I would expect to find in this case is a loose black wire somewhere in the amp.  A simple test you can do is to measure the DC voltage between terminal 12 and the black wire on the RCA jacks.  You can also poke and tug gently at the black wires in the amp with your meter probe while it's running to see if the small board randomly pops on at any point. 

 

[Kaitlineddy]

So, I reflowed the small board and found a couple of iffy connections on the black wires where some of the insulation looked to be pretty close to the solder joint if not mangled in it (oops!). I tidied those up and now the voltages are checking out! Thank you so much for your help!! On to the large board! 

 

[Kaitlineddy]

Update! Update! I ended up having the same issue with the large board, and I found a loose wire at the A100K potentiometer. I did just now learn how to trace things with the multimeter down the ground rail to find the fault, so along with everything else I learned about electronics through this kit, I just learned something else! Thanks again for your help.