S.E.X. 3.0 Kit: Right headphone driver is significantly quieter [resolved]

[Paul Birkeland]

You now need to repeat the test with the amp on but measure the AC voltage available at terminals 4 and 18 with the volume pot turned all the way up.  This voltage will be substantial enough that you'll want to be on the 20V scale.

If those are equal, then check 3 vs. 17. 

If those are equal, then check each of the positive binding posts.

At least one of those checks with yield and imbalance.  I have them listed in order so that once you find the imbalance, you can stop and we can debug, as all of the following steps will continue to show an imbalance. 

[Jet]

Before trying the next test you recommended I decided to repeat the previous one with the 60Hz tone and without voltage, I'm now getting 0.575-ish volts AC with a small fluctuation in the thousandths decimal place. Would this indicate the issue with my amp? What's causing this?

[Paul Birkeland]

What AC signal voltages do you see at the terminals listed?

[Jet]

Terminals 4 and 18 were around 8.30 AC with some variation around 0.01 and 0.04 AC volts on the 20 volt scale.
Terminal 3 was about 16.6 AC with some variation around 0.01 and 0.09 volts AC on the 20 volt scale. At terminal 17 I had to switch to the 200 volt scale to get a reading and it was around 157 volts AC with some variation of about 0.1 to 0.6.

[Paul Birkeland]

This narrows things down a bit.  Seeing the same voltage coming out of 4 and 18 tells us that the first amplification stages are working properly on each channel.

The 10x lower voltage is a bit puzzling on the second stage.  You could get a pretty big difference if the 1000uF cap on that side wasn't well connected, but not that much of a difference.  I think the next test I would do is to temporarily remove the white wire attached to terminal 10 on the output transformer of that side, then recheck the voltage at terminal 3.  We would generally expect this voltage to rise a bit with that wire disconnected, but if it pops up to 150+ volts AC, that would be helpful information.  If the voltage at terminal 3 doesn't change with that wire disconnected, then there's a bad solder joint around that socket or an untrimmed lead possibly touching the chassis or a neighboring terminal that is not allowing the signal to reach the output transformer.

[Jet]

Terminal 3's voltage didn't change with the white wire at terminal 10 of the corresponding output transformer being disconnected and terminal 17 is still reading 150+ volts AC.

[Paul Birkeland]

If you reconnect that wire, what AC voltage do you see at terminal 11 vs. 25?

[Jet]

Well I soldered the wire back at terminal 10 of the output transformer and I began testing terminals 11 and 25, I wasn't get much voltage out of either one and when I was testing 25 something in the amp suddenly started to make a slight popping sound and then there was smoke so I unplugged everything and turned it off. This doesn't seem like a good sign.

[Jet]

I now notice that the white wire going to the output transform that I just soldered again was in contact with the underside of the capacitor attached to terminals 35 and 36, could that have had anything to do with it?

[Paul Birkeland]

You'll probably want to go back and do a DC voltage check to be sure all the DC voltages are still correct.

[Jet]

I checked the DC voltages, they all seem to be correct and within the recommended values.

[Paul Birkeland]

Now with signal playing through the amp I would check the AC voltages present at 11 and 25.

[Jet]

When playing a 60hz tone through the amp with the source and potentiometer turned all the way up I got an initial reading of about 0.017 volts AC on terminal 11 but it then went down to about 0.03 and sometimes even 0 volts AC. Terminal 25 reads stable around 0.016 volts AC.

[Paul Birkeland]

Is the lead of the cap attached to terminal 3 touching the bare shield wire under it?  That will suck out all your signal. 

What you need to be looking for is metal bits on components touching each other when those components don't go to the same terminal.  This could also be leads poking through a terminal strip and touching things they aren't supposed to.

[Jet]

The cap attached to terminal 3 and the bare shield wire under it don't appear to be touching.