Crack right channel at full volume but left channel very faint hum

[Coldsnap]

Hello,

I took delivery on a pre-made Crack with no speedball. The right channel plays just fight, but the left has a very faint hum. Any ideas on what to check? Thank you.

[Paul Birkeland]

I would start by checking the resistances and voltages.

[Coldsnap]

I would start by checking the resistances and voltages.

Hello! Is there resources I can read up on measuring resistances and voltages? Also how to use the clips described in the manual. I read the measuring page and got a bit confused and a bit intimidated.

[oguinn]

Does the Crack have its terminals numbered? If so, use a multimeter that has clip leads (I use something like these) and clip the black lead to terminal 12U, then you can clip the red lead to the terminals listed in the manual.

You should start with the resistance measurements for two reasons: first, because there could be some issues that could fry your amp that would be revealed by the resistance measurements; and second, because there is no live voltage during that test (the amp is unplugged), so there's zero risk of shocking yourself. You can get used to measuring terminals safely. Read the instructions on page 47 and post the resistance measurements here (especially if they're not in spec).

Once you're confident resistance measurements are correct, then move to the voltage measurements. Take your time, turn the amp off in between terminal measurements if you don't feel confident. Remember that capacitors may hold a significant charge even after the amp is powered down. Follow the instructions in the manual, follow the safety tips on page 49, and you'll be fine.

[Doc B.]

[Coldsnap]

Thanks to both of you for the advice and the video! Great video Doc, that's exactly what I needed.

Just a quick question - can I measure the pins of the power tube to see if it was damaged in shipping somehow?

[Paul Birkeland]

You would need a tube tester to do that.  If the 6080 works in the amp, it's unlikely to be damaged.

[Coldsnap]

Ok, before doing a resistance test. I just did a visual inspection and found two things that don't look correct. I was wondering if these are something I should worry about and could also be a source of the problem?

#1

Red wire from N goes into #18 on the transformer when the photo shows it goes into #14. I've captured this in the photo where red circles are where it runs and yellow line is where it should run.
Also there's a small wire that plugs into transformer #16 and #15.

#2

Black wire runs from volume pot to A3 when it should run from volume pot to #3. I've captured this in the photo where red circles are where it runs and yellow line is where it should run.

[Coldsnap]

Here's the resistance check:

1. 1
2. 1
3. 0
4. 1
5. 1

6. 0
7. 2.94
8. 0
9. 2.93
10. 0

12. 0
13. 1
14. 0

20. 0
22. 0

B3. 2.94
B6. 2.92

Looks fine? I'm a bit nervous to do the voltage checks until I can get the visual discrepancies looked at.

[Paul Birkeland]

Yeah, that black wire to A3 is a problem.

The wiring on the power transformer will depend on your incoming voltage.  You have your transformer wired for 240V mains, where do you live and what did you measure with your meter during assembly?

The joint at 16L needs more solder.
20L needs more solder.
21L needs more solder.

[Coldsnap]

Yeah, that black wire to A3 is a problem.

The wiring on the power transformer will depend on your incoming voltage.  You have your transformer wired for 240V mains, where do you live and what did you measure with your meter during assembly?

The joint at 16L needs more solder.
20L needs more solder.
21L needs more solder.

Thank you for the reply! I am in 230V territory. What's up with the black wire you think? Since it's a ground, there's a ground mod installed. Which might be why it's done like that.

I plugged the crack in and now it's working just fine for 3 mins, then left channel died again.

The small tube is crazy hard to plug in / take out, is that common?

[Paul Birkeland]

That black wire is not where it's supposed to be.  I would not plug the amp in when it's wired like that.

It's also not wired for 230V, which is a different configuration that is available.

I would send this back.

[Coldsnap]

That black wire is not where it's supposed to be.  I would not plug the amp in when it's wired like that.

It's also not wired for 230V, which is a different configuration that is available.

I would send this back.

Ok, thank you. I misspoke, I'm in a 240v area.

I'm going to rebuild it.

[Paul Birkeland]

I'm going to rebuild it.

Or you could move one wire and see if it works?

[Coldsnap]

Or you could move one wire and see if it works?

Yea, that's what I mean. There's also that weird ground filtering mod too I will remove. And also solderer those bits.