Left Channel Out, Right Channel Super Loud [resolved]

[oguinn]

I'm posting this here but I'm unsure if the problem is in the SEX or the Quickie.

I turned the Quickie on this morning and then the SEX. There were two loud pops in the left channel, then the left channel went out, and the right channel was super loud even with the pot turned all the way down. The problem persisted when I unplugged my headphones.

I turned everything off immediately and plugged the source directly into the SEX to see if the problem persisted when I turned it back on, which it didn't. I then plugged the source back into the Quickie and reconnected the Quickie back into the chain. No problem.

I assume that something is messed up somewhere that was temporarily fixed when I plugged/unplugged the interconnects. Jostling the tubes and tapping the plates doesn't do anything. Given that the sound in the right channel was very loud, even with the pot all the way down, my guess is that the problem is in the SEX since it has a lot more gain than the Quickie.

Two questions before I yank both amps out and start prodding around:

• Is it likely that this is a SEX problem given the scenario I described?
• If so, where's a good place to start troubleshooting?

[Paul Birkeland]

You never specified which pot was turned all the way down.

This sounds like a flaky solder joint acting up. 

[oguinn]

Good point. It was the SEX pot that was all the down, the Quickie pot was all the way up (which is the way I normally have it).

I'm hopeful it's the Quickie and not the SEX since I'm replacing the Quickie with a Smash soon anyway, but I don't typically have good luck on these sorts of things.

[Paul Birkeland]

If the SEX pot was all the way down and one channel was still blaring, the ground connection on one level of the volume pot (on the SEX) is probably not well connected.

[oguinn]

Perfect. I'll start there. Thanks, Paul.

[oguinn]

I re-soldered the solid orange wires and am still experiencing the issue. I checked for continuity on the wires and it appears they're not broken. The LEDs are all lit on the C4S board.

I've started re-running my voltage and resistance checks. So far everything looks good except terminals 4 and 8 have an expected value of 0 but both have around 12V.

Any thoughts on what I should try next?

[oguinn]

Hm, also the center pin of the Right RCA jack is at 1.2M ohm

[oguinn]

Attaching photos

[oguinn]

Some of those were blurrier than I thought. Here's a clearer view of the pot.

[Paul Birkeland]

Hm, also the center pin of the Right RCA jack is at 1.2M ohm

I've started re-running my voltage and resistance checks. So far everything looks good except terminals 4 and 8 have an expected value of 0 but both have around 12V.

The center pin resistance on the RCA jack indicates a broken ground wire (and I'm starting to sound like a broken record).  What is the resistance between ground and the shell of the right RCA jack?

12V at 8 shouldn't be possible since it's connected to the chassis.  What voltage do you get between whichever terminal you're using for ground and the metal plate?  Do be sure you aren't seeing something like 12mV or 12uV.

[oguinn]

Sorry, I had a typo in there. It's not 8, it's terminal 18. And it was mV or uV, I had the scale wrong. We're probably set there it looks like.

When you say shell, are you talking about the outside of the connector on the top side of the chassis? I'll provide some permutations here.

Ground tab and center pin: 1.4K
Ground tab and outside of jack on the top: 0.5 ohms
Ground tab and screw threads (bottom side): 0.05 ohms

[oguinn]

Alright, as luck would have it I had a length of orange twisted wire so I soldered the new pair in and everything seems to be working. When I get back home I’ll trim the old pair back and zip tie the new wire to the existing Cat5

[Paul Birkeland]

What I meant was the resistance between the ground that you've been using for all your other measurements and the metal outside portion of the RCA jack in question (basically any metal part of the jack that isn't the center pin is fine).

[oguinn]

Got it. Thanks, Paul. The resistance checks are all back in normal parameters after replacing the orange pair. I appreciate your help (again)