voltage discrepancy OA/OB

[denti alligator]

Finished my build, which went fine. All checks out OK, except for a discrepancy in voltage on OA and OB.

OA measures 169, which is on target. OB measures 141.

I reflowed the join and ones directly connected. I switched tubes. No difference. Sound is poor in left channel.

How should I troubleshoot this? Thanks for help in advance.

 

[Paul Birkeland]

Is this an Eros 1 or 2?  Is this OA/OB on the board above the D socket? Or the boards up front? (Eros 1 or 2???)

 

[denti alligator]

Sorry. Eros 2.

The OA/OB are on the C4S board above the C socket.

Note: all other checks were on target. In the meantime I've reflowed OB and C6 and 25 U and L. (plus almost all joints on the B side)

If it's any help, the LED closest to the top right corner of the board is glowing only faintly.

 

[Paul Birkeland]

Can you post some photos of the top and bottom of the C4S board above the C socket? If you have one LED on that board that doesn't glow like the others, this is 99% a solder joint issue.

 

[denti alligator]

Photos coming soon. It looks like all 4 on that side are glowing slightly less. Where do I start looking for a bad joint? Or should I reflow everything on the board first?

 

[denti alligator]

Reflowed everything on the board's B side. That one LED isn't glowing. Could it be bad?

 

[Paul Birkeland]

You can measure the LED with your meter on the LED setting while it's installed on the board.  It should show 1.57V checked in one direction and nothing in the other.

Your images are 640x480, which is too small to really look at and get much of an idea about what's going on.  Is it possible to upload something with more pixels?

 

[denti alligator]

Here are some bigger pics. I have an extra LED so I can install that now.

 

[denti alligator]

Sure enough! It was the LED. I put another one in and all checks out. Spinning tunes now.

 

[denti alligator]

Dammit. Right channel dominates and left channel is too quiet. Balance is set right (on the main amp--Stereomour II--I double checked).

I tested this with a mono LP to be sure. What could be causing this?

Voltage discrepancy (though still within range) is now at

OkC  1.08
OkD  1.25

These are on the C4S board.

 

[denti alligator]

Next morning... the amp sounds pretty bad, with the right channel dominating over the left.

Resistance readings are all on target.

Here are voltages for the C4S board:

IA: 216.4
IB: 215.7
OA: 168.2
OB: 164.4
OC: 98.8
OD: 99
OkA: 99.9
OkB: 100
OkC: 1.207
OkD: 1.3

Only thing I can think I did wrong was that the heat sink wasn't fully snapped on to the B side of the MJ transistor on the shunt board during the first check or two of voltage. Could I have fried that transistor, or at least damaged it? The numbers all look right here, so why does the amp have imbalanced channels and sound so unimpressive?

 

[Paul Birkeland]

Solder joints.

 

[denti alligator]

Solder joints.

I've reflowed every one on the B side. I feel at a loss.

 

[Paul Birkeland]

The transistor is not fried.  Good voltages but troubled signal=bad solder joints.

 

[denti alligator]

The transistor is not fried.  Good voltages but troubled signal=bad solder joints.

OK, I'll go over them one more time. Thanks.

 

[Paul Birkeland]

You should also swap both the input and output cables at the same time to rule out that you have a flaky cable.

 

[denti alligator]

OK, I went over every joint, including removing the PC boards to get under them and reflowing the underside of each board. Same readings and same off-center sound. Is it time to send it in?

 

[Paul Birkeland]

Please be sure this isn't just a cable issue.  All of the Eros 2 kits that I have received for repair so far have been working perfectly.

 

[denti alligator]

I'll double check, but these are the same cables that were plugged into my Seduction, which worked fine.
I switched the input and output cables. Same problem. I'll try another set to be sure.