Need help troubleshooting! No sound in left channel :( [resolved]

[MikeSattler]

Hey all, looking to get some advice for a place to start troubleshooting here.

This is not a new build, my Crack + speedball has been working flawlessly for about 2 years now, but all of a sudden today the left channel didn't work when I powered it on. I've narrowed it down to the amplifier circuit itself as the issue (tried new interconnects, new DAC, new tubes, new headphones, etc...)

One of the LED's on the input tube socket is also not lighting up when the unit is powered on. I went through and measured voltages and some stuff is seriously wonky:

* Terminal 5 - 173V should be 75
* Terminal 9 - 172V should be 100
* Terminal 19- 85V should be 0
* Terminal 20 - 0V should be 206
* Terminal A1 - 175 should be 75
* Terminal A3 - 14V should be 1.56
* Terminal B4 - 175V should be 75
* Terminal B6 - 172V should be 100

Any help on where to start troubleshooting would be greatly appreciated!

[Paul Birkeland]

The voltage at terminal A3 indicates a damaged LED.  If they are installed with tension on the leads, then over time they can fatigue and break.

The easy solution here is to install a wire jumper between A3 and A8.

-PB

[MikeSattler]

Thanks PB! Will give that a try while I order a new set of LED's to replace the broken one.

[MikeSattler]

Installing that jumper did the trick!

Is the amp okay to use with this jumper installed until I can get a new LED to replace the broken one?

[MikeSattler]

I did notice that after installing this jumper there is sound coming out of the left channel when the volume pot is turned all the way down. Just wanted to make sure thats okay as a temporary fix...

[Paul Birkeland]

There isn't any issue when using this jumper, it can just make the amp a little harder to diagnose if it needs repairs in the future.

What you notice about the left channel is completely independent of what you have done with the jumper.  The pot just likely doesn't short all the way out when turned all the way down, but only on the left channel, or potentially the solder joint on the ground lug of the pot for the left channel is a little flaky.

-PB

[MikeSattler]

Thanks for the help so far! I installed new LED's on the 9-pin socket tonight and reflowed all the joints on the pot/headphone jack but there is still sound coming out of the left channel when the pot is turned down.

Sounds like the next course of action would be to replace the pot? I'm hesitant to without being sure since it's an Alps blue velvet but if that's the next step I'll give it a try.

Another weird thing though, not sure if it's related: I'm getting intermittent low-volume static that's coming out of both channels. Wasn't there before this LED broke and I haven't had a problem with RF in this room ever so it's very puzzling.

[Deluk]

If you reverse the channel connections on the pot that will prove if the pot is OK or not. With the wires off, check with a meter how the resistance changes. You could always fit the original Bottlehead supplied pot if you still have it.

[MikeSattler]

Thanks for the tip! Turns out the pot was bad, ordered a new one and it's working great now