Capacitor on 14U and 15U Smoking

[clamhost]

As the title said. Other than that my multimeter sucks. I will be uploading the checks I did. I didn't finish the voltage checks since the cap was smoking. Resistance checks seemed fine but again my multimeter is awful.

[Paul Birkeland]

Generally you'll smoke a cap when it's backwards.

There are other ways to make smoke from your amp, generally by having a short somewhere in the circuit that draws excessive current through the 270 Ohm resistors. 

If you post pics, we might be able to spot what's awry. 

[clamhost]

http://m.imgur.com/CFoodo0,rcaA2Ra,GI0Rcpv,qyU8Ddt,ISyVBAF,578HCl9,j0tK83R,7V3VfLK,KT5q14X

I uploaded a bunch of pics. The meter even told me a 270k resistor was 1.

[HiFi Builder Guy]

In looking at the 6th photo it appears (I can't see under the cap to be sure) the black jumper may be connected from T15 to T12 (should be T14 to T12 as shown on P.29 of the manual) 

[clamhost]

Its on T14.

-Thomas

[HiFi Builder Guy]

OK, I also noticed the untrimmed lead on B3 appears to be close to, or possibly making contact with the bare wire connecting B5 to B2.

[clamhost]

Its not from what I can see. Took a closer pic as well.

http://m.imgur.com/OVqrCY5

[clamhost]

Help?

[Doc B.]

If your multimeter is bad get a better one. We need reliable measurements to be able to help. Typically caps don't smoke, resistors do. Are you sure the smoke is not from the white resistor under the cap? If that resistor is having to much current drawn though it from a short somewhere further on in the circuit it could overheat. Look for miswires and look for wires and leads shorted to the chassis or touching terminals that they should not be touching.

[Paul Birkeland]

It would help to get more shots of the power supply as well.

If you want, you can disconnect the red wire leaving 13U, then turn the amp back on and test the power supply unloaded.

As others have pointed out, you have a lot of extra pieces of wire here and there that really should be removed, as eventually they may move and contact other parts. 

It's also possible that the leads on the 270 Ohm resistor crossing over the power transformer are touching something other than the two terminals that they are soldered to, and that would also cause some potential issues. 

-PB

[clamhost]

Good news. Asked my grandfather if I could borrow his nice Craftsmen meter and I passed all the checks. Bad news is when I put my HD800 in I can't put it in all the way or I don't hear anything. I have to put the headphone jack in almost all the way to get stereo sound. I believe my TRS jack is bad on the crack.

Opinions or perhaps I'm wrong?

Thanks,

Tom

[Paul Birkeland]

This is covered in the Crack FAQ. 

When you have the plug 1/2 way in, you feed one channel to both ears (ring to both tip and ring).  IIRC, this means there's an issue with the left channel. 

To diagnose this, you'll want to download a 60Hz test tone and feed it into the Crack.

Measure the AC voltage from ground to the center pin of each RCA jack, then to each of the outer lugs of the pot, then (with the volume up all the way) out the center lug of each level of the pot.

After that, measure the AC voltage at terminals 6 and 10.

-PB

[clamhost]

Alright I'll start working on it

[clamhost]

To diagnose this, you'll want to download a 60Hz test tone and feed it into the Crack.

Measure the AC voltage from ground to the center pin of each RCA jack, then to each of the outer lugs of the pot, then (with the volume up all the way) out the center lug of each level of the pot.

After that, measure the AC voltage at terminals 6 and 10.


Craftsmen Multimeter set to VAC 200.

RCA White Jack had AC of 01.0
RCA Red had AC of 01.1
The pot had 01.1 on all red and white wires.
All ground (including ground on RCA jacks had 0.00 AC)
Terminal 6 had AC of 09.6
Terminal 10 had AC of 09.2

[Paul Birkeland]

Ah, good!

This means that voltage is getting to the terminal strip.  Triple check the red and white wires leaving 6 and 10.  Also, if you did the grounding modification (forum sticky), try undoing it to see if that helps.

-PB