Resistance Question - Voltage Error

schweigc · 5861

0 Members and 1 Guest are viewing this topic.

Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19409
Reply #15 on: December 02, 2015, 02:33:14 PM
Could this be a bad capcitor, rectifier or resistor?
You can temporarily remove the red going to IA on the big board of the offending side, then check the voltage at the 220uF capacitor after the 270 Ohm resistor that is smoking.  In my opinion, you will not find an issue with this testing, but it will eliminate the capacitors, rectifier diodes, and resistors in the power supply.

The second time the 270 Ohm resistor blew all LEDs except the one attached to A3 lit until the resistor died.
It's really important not to fixate on which LED's do and don't light up.  You have a short in your amplifier that is drawing enough current to blow up a 5 Watt resistor quite quickly.  This would tend to be a significant wiring error or two components touching that shouldn't be. 

It can often be helpful to post some photos of your build also, in particular the high current C4S board on the offending side, as well as the small PC board in the middle (top and bottom), and the 7 pin and 8 octal socket. 

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline schweigc

  • Jr. Member
  • **
    • Posts: 22
Reply #16 on: December 02, 2015, 03:24:25 PM
Thanks again for the quick replies. I will be out of town for the next couple of days, I'll tackle it again with a fresh set of eyes when I get back. If I can't find anything, I'll post pictures. I love my Crack and can't wait to hear this one.

Chris Schweigert


Offline schweigc

  • Jr. Member
  • **
    • Posts: 22
Reply #17 on: December 05, 2015, 05:12:00 PM
I swapped the high current boards and I get the same voltage readings. So I have been focusing on the low current board. I have noticed that the A & B sides are symertrical except for the outboard -reg. On the A side it is attached to 1U but is empty on the B side. Is this accurate?

Chris Schweigert


Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19409
Reply #18 on: December 06, 2015, 06:35:02 AM
There should be a jumper to -reg.  If you didn't have this jumper, you wouldn't have the issues that you're having, but if this jumper isn't in the correct place, it could cause some issues.

Regardless, the C4S that is IA/OA should limit the current drawn from the power supply, which makes me suspicious that there is an error on that PC board.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man