Completed Stereomour—left channel crackles/pops/hisses/distorts [solved]

[funandfunny20]

Hey Guys & Gals,

I finished my Stereomour this past weekend.  I stayed up way to late…but it was all worth it—such a fun couple of days.

Everything sounded great and was working fine until last night.  After about a half-hour of warm-up, the left channel starts to crackle/pop/hiss/distort.  I swapped the tubes, but the problem still persists on the left side.  I haven't measured anything since the problem started last night…I'll try to take some measurements before I go to bed.

Is it likely a bad resistor or capacitor? 

The noises are not effected by volume.  They're loud regardless. 

Please advise!

[Paul Birkeland]

This is probably a funky solder joint.  Voltage measurements will be very helpful.

-PB

[funandfunny20]

Here are the voltage measurements.  T2 and OB are the problems….

“HV+” Settled at 400 and 398
T 1: 369
T 2: Only 3
T 3: 0
T 4: 0
T 5: 60
T 6-10: 0
T 11: 59
T 12: 0
T 13: 0
T 14: 218
T 15: 364
T 16: 60
T 17: 395
T 18: 0
T 19: 394
T 20: 60

A1: 60
A2: 365
A3: 0
A4: 60

C1: 60
C2: 358
C3: 0
C4: 60

IA: 388
IB: 380
OA: 217
OB:1
kreg (on OA/OB side): 0.8
kreg (on IA/IB side): 2.5
both regs: 0


From what I can figure, it looks like either the film cap itself, or some of the red-wire leading to it, aren't soldered properly.

[Paul Birkeland]

You'll want to resolder the center leg of the MJE5431A on the B side.

Also make sure the wires leaving Kreg go to pins 3 and 8 on the 9 pin socket.

[funandfunny20]

Well, I think i really messed things up…I think I got solder between OB and OA…because it started to smoke from in-between the two…now my board is black between them.

Suggestions?

[funandfunny20]

I've inspected the board…there is no solder between OA and OB….but it is sparking. 

What might cause this?

[funandfunny20]

Here are some photos of the board:

[funandfunny20]

What should I do now?

[2wo]

That black carbon may be forming a conductive path. You might try scraping it away with a sharp knife point or small screwdriver. you need to be pretty through and get down to clean board or it will arc over again. Or as long as there no trace on the underside of the board you could take a hacksaw blade and cut a slit between the two connections until you get past the burnt area...John 

[Paul Birkeland]

Post any voltages that you have that are not consistent with the manual.

[funandfunny20]

I got all the carbon off and now the board at least doesn't spark!

While doing this, and also going over the manuel again, I noticed that I had the both tube sockets incorrectly installed…now the sockets are correctly installed.  However, now all my resistance checks are way low.  For example, A1, A4, C1, and C4 are only reading .6, not 1.2.  A3 and C3 are out of spec as well.  Terminal 1 and 15 don't read anything.

What have I messed up now?



I feel like a complete idiot….apologies in advance.

[Paul Birkeland]

While doing this, and also going over the manual again, I noticed that I had the both tube sockets incorrectly installed…now the sockets are correctly installed.  However, now all my resistance checks are way low.  For example, A1, A4, C1, and C4 are only reading .6, not 1.2.  A3 and C3 are out of spec as well.  Terminal 1 and 15 don't read anything.

That can be a pretty grievous error... 

I would try a fairly brief voltage test to see what things look like, it's entirely possible that having the 4 pin sockets backwards roasted your 2A3's.  If you measure the resistance between the fatter pins of the tubes (out of the sockets, just in your hand), what do you get? 

[funandfunny20]

Yeah…that's what I am afraid of…

The tubes jump all over the place, but then after about 5 seconds finally settle at zero.


I just did a quick voltage test—doesn't look good.  To make sure I didn't break anything, I only took a couple of readings:


HV+” 0


A1: 0
A2: 0
A3: 0
A4: 0

C1: 0
C2: 0
C3: 0
C4: 0

both regs: 0


I think I should just pay the $125 and have you guys fix this.

[funandfunny20]

Oh, and I forgot to mention that the two LEDs closet to the output transformer are not lighting up.

[Paul Birkeland]

You could do that, but I'm pretty sure that you have a blown fuse.