No Left Channel - Voltage Errors [solved]

[vvhistler]

Hello All!

After quite a bit of research here and tinkering, I need some help isolating the issue with my build.

After completing the stock Crack, I ran into the issue with A3 not lighting and no sound left channel. After some chopstick poking and reflows, it eventually came on and everything worked great.

I installed Speedball and I'm back to A3 being out and no left channel. All Speedball lights are on, however it should probably be noted the small board connected to T5 comes up a few seconds after the other small board, which comes up immediately with A8. The 12AU7A tube I have does seem to light up completely (two filament sides) however it looks upside down compared to other pics in the forum.

Voltages are:

T   Expected   Measured
1   75   83
2   170   182
3   0   0
4   170   181
5   75   176
6   0   0
7   100   112
8   0   0
9   100   175    ****
10   0   0
11   0   0
12   0   0
13   170   183
14   0   0
15   185   200
19   0   91
20   206   0
      
A1   75   176     ****
A2   0   0
A3   1.56   0     ****
A4   0   0
A5   0   0
A6   75   82
A7   0   0
A8   1.56   1.53
A9   0   0
      
B1   75   82
B2   170   182
B3   100   112
B4   75   177     ****
B5   170   182
B6   100   175    ****
B7   0   0
B8   0   0

I've tried the following suggestions from other forum posts:
*Reseated the 12AU7A tube many times
*Reflowed grounds, terminal pins, socket pins, POT pins, headphone jack pins.
*Jumpered A8 to A3: the A3 LED does light, however still no sound from left channel.

Any suggestions?

[Paul Birkeland]

You should resolder the center leg of the MJE-350 on the small board feeding T5.

-PB

[vvhistler]

Hi, and thank you PB! Per suggestion, middle via has been reflowed, joint looks shiny and in spec. Still no luck.

Are there any other common points of failure aside from the small tube socket?

[vvhistler]

Alright, crisis averted.

Turns out the 12AU7A tube just needed a little thump. Light came back on and all is well.

[Strikkflypilot]

If the tube needed a thump, You probably still have a bad contact/solder somewhere or the tube is flaky?

[vvhistler]

Right, I can't prove 100% that it's the tube until I get another. Might be time to check out the tube rolling section