Diagnose problem for no sound in left channel [resolved]

[danhead]

My crack (built circa 2012) has no sound in the left channel. Both tubes are lighting up, and I made sure the audio source was good, and everything checked out fine there. What are the steps to diagnose such a problem, or which part of the circuitry should I test first?

Thanks in advance for your kind help

 

[Doc B]

As always, start by measuring voltages and post any that are out of spec by more than 15%.

 

[danhead]

I highlighted the unusual results in red
Resistances
1. *
2. *
3. 0
4.
5.
6. 2.5
7. 2.9
8. 0
9. 2.93
10. 2.5
12. 0
13. Falls from around 5k
14. 0
15. 0
20. 0
22. 0

b3. 2.9
b6. 2.9

Ground lug - 0
Center pins - 96/94

Voltages
1. 154.6
2. 171
3. 2
4. 171
5. 82
6. Fluctuating around 0
7. 154
8. 2
9. 104.9
10. Fluctuating around 0
11. 0
12. 0
13. 170
14. 0
15.195
20. 0
21. 220

A1.82
A2. 0
A4. 0
A5. 0
A6. 154
A7. 0
A9. 0

B1. 154
B2. 170
B3. 150
B4. 81
B5. 170
B6. 104
B7. 0
B8. 0

 

[Paul Birkeland]

Does this Crack have a Speedball?


The voltage at terminal 1 is the issue.  That half of the 12AU7 isn't operating properly.  Do both diodes on the 9 pin socket glow?

If yes, and you have a Speedball, the most common issue is the wrong R1 being installed.


If one LED is out, then I would suspect that the wired connection between A4 and A5 has come loose or wasn't properly soldered.  Another possibility is a damaged LED, which will manifest as seeing 12V at A8 in your case.  The ground reference could also be compromised, which will show up as some DC voltage far from 0 at A7.

 

[danhead]

C.B., thank you for your insight and response. I do not have the speedball upgrade. I will check the diodes and a4/a5 connection when I get home later and report back.

 

[danhead]

C.B.
The LED between A8 and the center connector is not lighting up. This should be lighting up, correct? I attached a photo

 

[Paul Birkeland]

The wire at A5 is not soldered well.

 

[danhead]

Problem solved - it was the 12au7 tube that was bad. I had bought another, replaced it, and sure enough, both channels are working. Thanks for your suggestions before.

 

[Paul Birkeland]

I would reflow the joint at A5 and try the tube we provided again.  They are all tested (sometimes twice) before being shipped.

 

[danhead]

Oh no, I spoke too soon! The sound started fading out. If I jiggle the 12au7 a little, I'll hear sound in the right channel, but then it fades away to only the left channel. Maybe that's helpful information?

 

[Paul Birkeland]

Yes, as I said before, I would reflow that joint at A5.  It's not all the way soldered. 

 

[Kitchener]

What Joshua said, it's time to heat up ye olde soldering iron.


I had a similar problem with my Crack.
In my case one of the big wirewound resistors had a flaky solder joint.
As I jiggled the tubes, I'd get loud pops and the sound in one of my channels would fade in and out.

Cocksure of my soldering, I figured the problem might be the tubes or some component.
Alas, the joint needed the iron.


Reflowing is always a good idea.
Most of the components in the Crack, apart from the plastic bits (switch and LEDs, mainly), can take a good, hard, long, hot pounding from the soldering iron. Go at it.

 

[danhead]

I'm sorry for my delayed response. Last night I had time to resolder the A5 point and, fingers crossed it doesn't fade out again, I can hear sound out of both channels and so we're up and running, thanks to the gracious help and support of you guys.

Kind thanks,

 

[attmci]

What Joshua said, it's time to heat up ye olde soldering iron.


I had a similar problem with my Crack.
In my case one of the big wirewound resistors had a flaky solder joint.
As I jiggled the tubes, I'd get loud pops and the sound in one of my channels would fade in and out.

Cocksure of my soldering, I figured the problem might be the tubes or some component.
Alas, the joint needed the iron.


Reflowing is always a good idea.
Most of the components in the Crack, apart from the plastic bits (switch and LEDs, mainly), can take a good, hard, long, hot pounding from the soldering iron. Go at it.

Not a good idea to jiggle the tubes. The loud pop may damage your headphone's driver.

 

[Kitchener]

Might want to have some disposable headphones for troubleshooting, in case they get blown to shit.