Stereomour Diagnosis Testing or Repair?

[audiotecture]

Swapping the 2A3s the reading at A1 is 1.167, A2 * (number keeps getting bigger), A3 248.7, A4 1.167. I don't know if it means anything, but when I did my resistance check, terminal strip 2 & 14 settled at 687K ohms rather than 486K ohms. Terminal strip 7 & 9 are at 15.79 and do not change when the potentiometer is turned. I've also included a photograph of 4 pin socket A. One of the soldering holes broke off at A2 so both wires are soldered to the remaining hole. Not sure if this makes difference?

[Paul Birkeland]

Swapping the 2A3s the reading at A1 is 1.167, A2 * (number keeps getting bigger), A3 248.7, A4 1.167.

Voltages?

[audiotecture]

Paul...I'm not sure if this is the information you are looking for, but I've detached the black wire from K on the power supply board on the A side and I get the following readings A1 = 59.6V A2 = 362.2V A3 = .008V A4 = 59.5

[Paul Birkeland]

That's a perfect set of DC voltages.  before you had over 100V at A1/A4.  Now you can put the K wire back and recheck the DC voltages again.

[audiotecture]

Paul...I replaced K on the A side of the power supply board and now have the following readings A1 = 59.27V A2 = 360.2V A3 = .007V A4 = 59.30V for reference C1 = 60.57V C2 = 363.1V C3 = .007V C4 = 60.42

[Paul Birkeland]

Those are working voltages.

[audiotecture]

Paul...Given the similar measurements on the A & C sides, I attempted to play music and observed the following: If I plug speakers into the A-side and C-side speaker binding posts, sound comes out of the A-side but not C-side. If I take the C-side red cable and touch it to the A-side red binding post, I get sound from both speakers. Touching the C-side black cable to the A-side black binding post does not produce any sound from the C-side speaker. 

[Paul Birkeland]

Turn each hum pot all the way clockwise.  Do you hear hum in both speakers?

[audiotecture]

Paul...yes I hear hum in both speakers.

[Paul Birkeland]

There's wiring that leaves pin 1 and pin 6 on the 9 pin socket to send signal to each 4 pin socket.  I suspect that yours is loose on the side without sound.  Since you can hear hum and I'm guessing it's roughly the same level, the 2A3s are operating properly and the output transformer wiring is OK. 

If the DC voltages at OA and OB on the 9 pin socket are OK, then that leaves the wiring leaving pins 1 and 6, or possibly signal isn't making it into the 9 pin tube from the input selector and volume pot.

To test the input selector and volume pot, temporarily install a jumper between terminals 7 and 9. This will sum both channels and send that mono signal to both sides of the amp.  If your dead channel awakens, then you need to inspect the wiring from the RCA jacks to the selector switch, the selector switch to the volume pot, and the volume pot into the amp.  If both channels stop working, that is also an indicator of an issue with the input wiring.  If the same channel is still dead, that's an indication of a remaining wiring issue around the 9 pin socket, or possibly the .1uF coupling cap.

-PB

[audiotecture]

Paul...DC voltage at OA = 212.1V & DC voltage at OB = 209.7V. The jumper between terminals 7 and 9 worked sound came out of both the A-side and C side. I checked all of my wiring and connections from the RCA jacks to the selector switch and selector switch to the volume pot and volume pot into amp. Almost perfect good news. RCA jacks 2 & 3 are sending a signal to both speakers. RCA jack 1 is still only sending a signal to one of the speakers. I don't have any more time tonight to troubleshoot RCA jack 1, but I'm assuming I'll just need to re-check all my solder joints and connections. Is it possible to damage an RCA jack during soldering?

[Paul Birkeland]

Yes, you can damage a jack.  If solder flows between the center of the RCA jack and the shell, it will short out the signal.  99% of the time, this is what we see going wrong.  If you measure the DC resistance between the center pin of the jack and the outside body of the jack with the selector switch not on that input, it should give you a very high resistance (or over limit).  If solder has shorted the jack out, then you'll see something close to zero ohms.

I have also seen debris get into the bottom side of the jack between the center pin and shell, and that was enough to create the same problem.