Just finished my S.E.X.

[Grainger49]

Sometimes a friend is the right friend for this case.  You may be looking at the problem and seeing something else.  After you do an inspection, if you find nothing let a friend do it too.

[JC]

Could not agree more, Grainger.  Even a non-techinical friend brings fresh eyes to the table.

I can't count how many times I've over-looked the same obvious problem, then had someone else spot it for me.  After you've worked on something closely for a while, I suspect everything starts to look just as it should, even if it isn't correct.

[SilverS]

Thanks for the suggestions, I'll have my dad give it a look over and see if he can find anything. I'm assuming he should just trace the circuit as best as possible?

[Grainger49]

I meant that your dad should look for odd looking solder joints and connections that have no solder.  If he can trace circuits that is good too. 

[JC]

If he can trace the circuit, that would be great.  Alternatively, you may just want to read each of the wiring steps to him in order, and have him follow along in the actual amp.  That will end up giving you a terminal-by-terminal look at each connection, I think.  Take the steps in order, and don't move on to the next step until you are both satisfied that the one you are working on is correctly executed.

A little time consuming I realize, but you should find anything that looks suspicious to you.

[SilverS]

Ok first thing we did was hook some speakers up before doing anything and guess what?

The right channel on the speakers is working, but not the left. And the left channel is still the only one that comes though when I plug in headphones.

Where should we go from here?

[JC]

Well, I would certainly suggest inspecting all the wiring to the headphone jack, the headphone jack, and the wiring that goes from the headphone jack to the speaker terminals.  Since a bunch of that is done in twisted pair in which both wires are black, I can see where it would be easy to make a mis-step.  When in doubt, of course, use your Ohm meter on each end to make certain that you are working on the same wire.

[SilverS]

I could also just be that headphone jack is shot, I probably resoldered the bottom terminal 4-5 times (miswiring/resoldering etc). I'll definantly check the wiring tomorrow though.

Thank you very much to everyone for all the help, I can't tell you how relieved I am to have you all around for advice

[SilverS]

Ok, I check the wires connected to the headphone jack and turns out one wasn't soldered, but that didn't fix anything, I think its just that the headphone jack is completely shot from all the soldering/desoldering/resoldering I've done to those connections.

[SilverS]

Alright big update! Both channels are working

The only problem is the 120Hz hum is still in the left channel. Where should I check to fix this issue?

[Paul Joppa]

Did you replace the headphone jack to get both channels working?

Here are things I've posted before, not sure if you've done all of them:

>> To start looking for hum and buzz, disconnect everything except the speakers or headphones and turn the volume all the way down. That isolates the electronics from possible external noise sources.

Try to measure the output hum at the speaker terminals, using the lowest AC voltage scale you have. (It may be too low to measure with your meter, but if we get any data it will help figure this out.)

>> A7, B7, C1 and C4 should all be connected to chassis ground by the wire from C1 to safety ground, and you should read nearly zero voltage, AC or DC, at these points. Check wiring and soldering.

>> Your readings at 2, 9, and 10 appear to be AC; the manual gives appropriate DC measurements but not AC. But T9 (connected also to T12) should be at AC ground through the 1000uF capacitorT12 to T15. Check those connections and solder joints, also the orientation of the capacitor. T10 is on the ground buss, ultimately connected to T18 which is screwed to the chassis plate so there should be no voltage, AC or DC at these points. (Are you sure the measurements are volts and not millivolts?)

[SilverS]

I just went down to give the amp one more test before going to sleep and its back to only working on the left channel again... This afternoon it transmitted on both channels when I plugged in my earbuds. So could it just be the low impedance of the Grado's that is messing up the transmission? Also, I'll do what you said to test for miss solders tomorrow afternoon and see if I can't get rid of the hum.

[Doc B.]

I'm wondering if it might be something about the fit of the headphone plugs in the jacks. Maybe check to see if the earbuds/both channels and Grados/one channel situation is consistent. I had a brand new set of cans at the Head Fi meet a couple weekends ago. Halfway through the day they went mono. Cans were fine, amp was fine. Turned out someone had overstressed the 1/8" to 1/4" headphone plug adapter and shorted it to mono.

[Grainger49]

I can't help but wonder if the Grados work on other headphone outputs?  The lack of Left channel might be the Grados.  Then again it might not be the Grados.  I just have to ask.

[SilverS]

I believe I have found the problem causing the hum:

T21 ~ 143V (supposed to be 183V)
T22 ~ 143V (supposed to be 183V)
T29 ~ -14V (supposed to be -17V)
T12 ~ -14V (supposed to be -17V)

So, I should just check all my solder connections to the terminals on the B side or could it just be that power isn't properly getting to that side? Sorry for asking yet again but I don't know where to start looking.

As for the left channel only transmission, it's probably just that the Grado's plug and the headphone jack aren't playing nice, I'll have a new jack by the end of the week though so that should fix any issues there.