Faulty Left Channel

Mesz77 · 612

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Offline Mesz77

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on: February 25, 2021, 07:51:52 AM
My crack has decided to give out after a year or so. The left channel hasn't been working at all. Whenever I built my crack I got suckered into doing a bunch of mods for it, which included two large film caps at terminals 6&7 and 9&10. I used zip tie mounts to secure the caps to the plate, but after a while the cap connected to 9&10 started to dangle from the plate because the adhesive wore off. Around this time is when the left channel gave out. So I figured it was due to the hanging cap.
I flipped the plate over and turned it on to do a little testing.  I poked both wires coming from the cap and whenever I poked the one leading to terminal 9, the left channel kicked in! So I took the heat shrink tubing off both ends of the capacitor. When I put the capacitors on when I first built the crack I had to solder some extra wire to both ends of the caps since their leads weren't long enough. I figured that there was a faulty connection so I twisted the wires together and soldered them for both ends. I used gorilla glue to secure the caps to the plate and figured I was all good to go. I was not.
The left channel is not working again and I cannot figure out why. All the LEDs are lit up, but the ones on the board without the heatsinks are pretty dim. My voltage checks for both boards are all good. One thing that has occured a few times while messing with the components is that ive gotten zapped even though the amp is turned off and unplugged from the wall. I really want to return to audio nirvana asap so any help is greatly appreciated!!

Brandon Meszar
PSU


Offline Paul Birkeland

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Reply #1 on: February 25, 2021, 08:33:24 AM
Can you post all the voltages from both PC boards?

A properly built/running Crack, especially with the Speedball, should discharge the HV power supply within a minute or two. 

Have you considered just using the 100uF caps we provide with the kit?  Big film caps tend to make for an unreliable Crack.  If you have to have them, there's ample space in the Crack-a-two-a.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Mesz77

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Reply #2 on: February 25, 2021, 08:52:00 AM
I have not used the caps that were provided, but if it ends up being the difference between the amp working or not, I will put them in.

Small Board:
OA - 69.2
IA - 181
B-A/B - 0
IB - 181.2
OB - 70.7

Large Board:
OA - 104.9
OB - 102.6
G - 0
B+ - 180.8

Brandon Meszar
PSU


Offline Paul Birkeland

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Reply #3 on: February 25, 2021, 09:41:11 AM
It may indeed be just that.  In the absence of a voltage problem, it tends to be input/output wiring that causes a problem like this (or something outside the amp like cabling).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Mesz77

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Reply #4 on: February 25, 2021, 10:09:56 AM
I switched out the film capacitor for the stock capacitor and the left channel is still not there. I made sure to solder the banded lead to 10U and the unbanded to 9U

Brandon Meszar
PSU


Offline Paul Birkeland

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Reply #5 on: February 25, 2021, 12:18:34 PM
Can you post some photos of what you have going on right now?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Mesz77

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Reply #6 on: February 25, 2021, 12:31:11 PM
Let me know if you need more than these

Brandon Meszar
PSU


Offline Paul Birkeland

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Reply #7 on: February 25, 2021, 12:38:19 PM
I see Doc B. has increased the maximum image size we accept on the forum!

So you have an Alps blue pot installed without a PC board.  Those break when you connect wires to the pins.

Is that a pilot light you've added?

The white wire on the headphone jack looks like it might not be super well soldered.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Mesz77

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Reply #8 on: February 25, 2021, 12:53:30 PM
Lol I didn't realize the images were so huge! The white wire to the headphone jack looked and felt pretty solid, but I reflowed it and still no left channel. I suppose I'll reflow all the pins to the alps pot now. That is a pilot light that I installed since I kept on forgetting to turn the amp off!

Brandon Meszar
PSU


Offline Mesz77

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Reply #9 on: February 25, 2021, 01:32:57 PM
I think I may have found the issue but I want to double check. Whenever a pair of headphones is plugged in, are all three of these pins on the jack suppose to look separated like in the image?
I wasn't getting anything through the left channel after reflowing parts of the alps pot, but while listening I poked the very top pin in the headphone jack so it would touch the plate across from it. It was separated like the other two pins, but not as wide as them as you can see in the image. I got audio in both channels whenever this happened, and the pin went back to being separated like it was before after poking it. The audio remained in both channels so I ran a left/right channel test from youtube through the amp to make sure it wasn't the right channel coming in through both channels. It's definitely working now, but the top pin on the jack concerns me. If I pull a little bit on it to separate it more I lose the left channel completely.

Brandon Meszar
PSU


Offline Paul Birkeland

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Reply #10 on: February 25, 2021, 01:43:20 PM
The tip contact won't separate as much as the ring and the sleeve do.  That's normal and what I see in your photo. If you poked that top contact down so it touches the other side, that will cause your left channel to short to ground and it will drop.

I don't suppose you're using a 1/4" to 1/8" adapter?


Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Mesz77

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Reply #11 on: February 25, 2021, 01:45:30 PM
No adapter...

Brandon Meszar
PSU


Offline Paul Birkeland

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Reply #12 on: February 25, 2021, 01:50:47 PM
With your headphones plugged in, you can measure the DC resistance between ground and the tip, then ground and the ring.  They should be about the same. 

The ring is the connection on the HP jack where the red wire lands.

The tip is the connection on the HP jack where the white wire lands.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Mesz77

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Reply #13 on: February 25, 2021, 01:55:07 PM
Both the ring and tip are around 230 ohms. Both channels are still working, but the tip contact is very sensitive. When I touch it with the multimeter the audio cuts in and out.

Brandon Meszar
PSU


Offline Paul Birkeland

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Reply #14 on: February 25, 2021, 01:58:17 PM
If you wiggle the white wire connecting to the tip terminal does the audio cut in and out?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man