No sound after upgrade install [solved]

[mcwhart]

Hello,

Just installed upgrade kit on my S.E.X 2.1 kit.  Powered up, and there is low level hum with only a very faint signal heard through headphones with volume turned all the way up.  All four LEDs light up, and both tubes are working.  Any ideas?

After looking again, I realize I did something very stupid:  connecting wires to A6 and B6 instead of A5 and B5.  Ugh.  Anyway, might anyone know what damage I could have done, or what may need to be replaced?  I reconnected correctly, and I still get low level hum with only the faintest signal through headphones from the left channel only.  Tubes and LEDs working...


Thank you for your help!   

[Paul Birkeland]

Hello there,

How are the voltage measurements?

I do not anticipate that any harm has come to the PCB.

-PB

[mcwhart]

Hello,

I checked all the voltages.  Here are the ones that did not measure according to or near spec.:

On the 2.1 C4s,

Terminal 0A voltage is 0, should be 75

On the S.E.X 2.1,

Terminal 15 voltage is 9, should be 19;
Terminal A2 voltage is 310, should be 375;
Terminal A3 voltage is 9, should be 19;
Terminal A5 voltage is 55, should be 75;
Terminal B5 voltage is 65, should be 75;
Terminals A6 and B6 voltages are 2, should be 2.5;
Terminals A7 and B7 voltages are -3.8, should be -3.15;
Terminals A8 and B8 voltages are 2.25, should be 3.15;
Terminal C1 voltage is -3.8, should be -3.15;
Terminal C2 voltage is 2.2, should be 3.15;
Terminal C4 voltage is -3.8, should be -3.15;
Terminal C5 voltage is 2.5, should be 3.15.

Thanks for your help.  Please let me know if there is something else I should be checking.

[Paul Birkeland]

0V at OA means that you have a cold solder joint on the middle leg of Q2 on the "A" side on the PCB.

[mcwhart]

Thank you.  I removed and switched the q2 transistors, resoldered, and I am getting a satisfactory reading of 70v at 0B but only about 7v at 0A.

Just powered up and I am getting an audible hum through the right channel at zero volume, nothing from the left.  I get sound in the right channel when I increase volume, but again, nothing from the left.  Any thoughts?  Thank you

[mcwhart]

I just did another voltage check after getting low level hum at zero volume and sound with increased volume on right channel only.  No sound from left channel.  Tubes and LEDs all lit.

Terminal 15:  voltage is 9, should be 19

Terminal A5: voltage is 60.7, should be 75
Terminal B5: voltage is 70.4, should be 75

Terminals A7 and B7 both measure -3.89, should be -3.15

Terminals A8 and B8 both measure 2.26, should be 3.15

Terminal C1: voltage is -3.89, should be -3.15

Terminal C2: voltage is 2.3, should be 3.15

Terminal C4: voltage is -3.89, should be -3.15

Terminal C5: voltage is 2.49, should be 3.15



ON THE C4S:

0A voltage is 61.2
0B voltage is 70.6

Any suggestions would be much appreciated.  Not sure where to go from here.

Thanks!

[mcwhart]

Any advice?  Anyone?  Thank you.  I just don't know what I should be looking for.

[Doc B.]

Check the connection of the 0.1uF cap at A5. Sounds like a lead might be shorted.

[mcwhart]

I checked the connection as suggested, resoldered it, and still, I am getting no sound from the left channel, and low level hum from right channel with volume down and sound in right channel with volume up.  I rechecked resistances.  The only discrepancy I found was with 14 and 24, which are supposed to be variable.  14 was 1.8, and 24 was 0.5 with the volume turned all the way down.  Measurements at A7, B7, A8, B8, C1, C2, C4, and C5 are 4.10-4.18.

Voltage discrepancies are the same as in my last post.

Really at a loss here.  Unit was working fine until I tried unsuccessfully to install the upgrade.  Any suggestions much appreciated.

Thanks

[Paul Birkeland]

Can you post a couple photos of the channel that isn't working?

The 9V issue is independent from the C4S upgrade, but would cause some serious issues.

I would be triple checking that the 249K resistor on that side is still properly connected.

[mcwhart]

Triple checked point you recommended and all appears good.  Here are some photos.  Measurements and symptoms remain the same as in recent posts.  Thank you.   Oh....forgot to mention that I pulled upgrade board out of the way for photos.  Thanks

[fullheadofnothing]

The left channel output cap looks pretty scorched. Did that happen during the C4S install?

[Paul Birkeland]

What's the voltage at A1?

[mcwhart]

Yes, I nicked that cap with soldering iron while installing upgrade--would that impact sound?  Will check voltage at A1 and reply with that when I get home from work.

Thank you for your help.  I really appreciate it.

[mcwhart]

I switched the output caps and now I get low level hum in both channels.  Level of hum is constant, does not change with volume adjust, but it definitely more than it should be, more than it was before I installed upgrade.  Still getting sound from right channel only.  I checked voltage at A1 and it is as it should be, near 0, .008.  Any other ideas?

Thank you