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.

 

[funandfunny20]

So I checked the resistance of the fuse, and it jumps all over the place, eventually settling at zero.  I'm assuming it is not fried since I'm getting some reading, is that correct?

 

[Doc B]

Make sure you have good contact of the fuse ends and the test leads. I often rub the probes against each other to clear any oils that might be on them, and then rub the probes against the ends of the fuse to make sure there is nothing interfereing with the metal to metal contact.

 

[funandfunny20]

Hey Doc,

I just did what you said and while meter does jump up slightly, it almost immediately settles at 0.  I'm going to make a run to radioshack shortly to get alligator leads and new fuse.

 

[Doc B]

Clip leads are a good idea. It sounds like the fuse is probably OK, but a new one is cheap insurance.

If the new fuse doesn't bring things back to life the next step is to make sure the power switch is working. WITH THE AMP UNPLUGGED use your new clip leads to clip a test lead to each terminal on the power switch then measure the resistance when you throw the switch back and forth. In one direction it should be overlimit and in the other it should read close to zero ohms. If it reads overlimit on both settings it needs to be replaced.

 

[funandfunny20]

Okay, so the Radio Shack near me doesn't carry 1.5a GMA slow blow.  Only fast-blow.  I'm assuming that matters, right?


As far as the power switch goes, it does OL when switched, and it is at zero when flipped back.

I did some resistance checks, and A4, A1, C4, C1, and all the other points that are supposed to read 1.2k Ohms, only read .5k Ohms.

Does that help with anything?

Sorry for all the dumb questions!