News:
November 28, 2022, 11:04:38 PM

Author Topic: Crack Troubleshoot  (Read 84 times)

0 Members and 1 Guest are viewing this topic.

Offline esheu2

  • Newbie
  • *
  • Posts: 3
Crack Troubleshoot
« on: November 23, 2022, 10:48:56 PM »
Hello,

I built a Crack 1.1 for my friend a couple years ago at this point. Recently, she told me that she was having an issue with it not having any audio coming from the left channel. She seems to have tried to troubleshoot it herself to no avail. So I got it back in to take a look at it myself.

Inspecting the solder joints, I saw that 10U seemed lacking in solder. I reflowed the joint with some solder and then ran the resistance check that was detailed at the end of the build manual. There were no inconsistencies that I found.

Immediately after powering it up, I saw that the led connected to A3 was not lighting up. Then when I ran the voltage check, I got off readings at terminals 5 and 9. Both of them read ~150V when they should have been 50-100V and 90-115V respectively.

Another thing to note is that the XICON 10W 3K resistor connected at terminal 9L had completely faded printing compared to the corresponding resistor in the opposite channel.

If anybody could help me figure this out it would be greatly appreciated! Thanks  :)

Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 17610
Re: Crack Troubleshoot
« Reply #1 on: November 24, 2022, 05:02:14 AM »
What is the voltage at A3?  It will either be around 12V or 0V if it's not lighting up.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline esheu2

  • Newbie
  • *
  • Posts: 3
Re: Crack Troubleshoot
« Reply #2 on: November 24, 2022, 05:18:50 PM »
What is the voltage at A3?  It will either be around 12V or 0V if it's not lighting up.

It seems to be around 1mV

Offline esheu2

  • Newbie
  • *
  • Posts: 3
Re: Crack Troubleshoot
« Reply #3 on: November 24, 2022, 06:12:23 PM »
Plopped in another 12AU7 that I had on hand. All the voltage check readings are correct now. But, the left channel diode is still not lighting up.

I measured the voltage drop over the diode and got 1.14V. I swapped the leads around and got 2.8V.
The working diode got readings of 1.5V and 0V respectively.

Current theory is that the old 12AU7 died and took the diode with it somehow?

Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 17610
Re: Crack Troubleshoot
« Reply #4 on: November 25, 2022, 06:52:57 AM »
What are the voltages on terminals 1-5?  You shouldn't have correct voltages there if the LED isn't lighting up.

I'd also be interested in the DC voltage across the unlit LED with the amp running, not the voltage drop your meter gives in diode mode.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man