Voltage issues with new Crackatwoa after blunder [resolved]

Rd777 · 2986

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Offline Rd777

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While doing the voltage test check i accidentally touched the capacitor while probing the bB terminal, there was a spark. Before this the bB terminal on that high current c4s board read fine (150V).

Here are the voltage readings on that board after my blunder.

IA - 188.7V
OA - 116.3V
BA - 0V
IB - 0V
OB - 79.9V
bB - 116.5V

All LEDs are still functional.

Low current board
IA - 150.4V
OA- 67.4V
Kreg A- 4.6V
BbregA 150V
IB - 123.8V
BB-123V
Kreg-1.1V
OB-67.7

« Last Edit: June 27, 2023, 04:46:50 PM by Paul Birkeland »



Offline Paul Birkeland

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Reply #1 on: June 24, 2023, 06:21:49 AM
This will be a bit of a complicated diagnosis.  There are two completely identical high current C4S boards.  You will want to swap them from side to side to see how the voltages change.

If you swap the boards and KregB stays at 1.1V, then you need to replace the 431 regulator by KregB. 

If you swap the boards and KregB is 4.6V and KregA is 1.1V, then you will need to get in touch with replacementparts(at)bottlehead(dot)com about purchasing a replacement high current C4S board with parts.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Rd777

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Reply #2 on: June 24, 2023, 06:29:48 AM
Ah well.. Thanks for the response. Will get to it asap.

Any tips on unmounting the high c4s boards? Should I desolder the wires at the terminal strip or at the board?



Offline Paul Birkeland

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Reply #3 on: June 24, 2023, 06:30:18 AM
Heat up the joints on the board and slip the wires out, then remove the board.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Rd777

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Reply #4 on: June 25, 2023, 08:30:57 AM
Hi Paul, so after swapping both boards, all LEDs are still functional. The voltage readings are as follows:

Low current C4s
IA - 150.4V
OA - 67.2V
KregA - 3.7V
bRegA - 150.4V

IB - 115V
OB - 68.3V
KregB - 1.1V
BregB - 115.5V

-------
High Current C4S (A side)
IA - 184.9V
OA - 150.V
bA - OV
IB - 0V
OB - 91.3V
bB - 150.5V
High Current C4S (B side)
IA - 187V
OA - 115.8V
bA - OV
IB - 0V
OB - 79.6V
bB - 115V


So as per your analysis it seems as though the problem is the LM431 regulator.

If that is the case can I use this as a replacement? (I live in Canada).

https://www.mouser.ca/ProductDetail/onsemi-Fairchild/LM431ACZ?qs=fAPocZeZcjirQBCPnqK0uQ%3D%3D



Offline Paul Birkeland

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Reply #5 on: June 25, 2023, 08:34:07 AM
Yes, give that a go and you should be back up and running.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Rd777

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Reply #6 on: June 25, 2023, 08:35:24 AM
Excellent, thanks for your help. Will report back when i get the replacement.

Have a nice Sunday!



Offline Rd777

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Reply #7 on: June 27, 2023, 12:57:49 PM
After replacing the LM431 by the KregB side I have the following readings.

Low current C4s
IA - 150.4V
OA - 67.2V
KregA - 3.7V
bRegA - 150.4V

IB - 150V
OB - 69.4V
KregB - 4.7V
BregB - 149.9V

-------
High Current C4S (A side)
IA - 184.9V
OA - 150.V
bA - OV
IB - 0V
OB - 91.3V
bB - 150.5V
High Current C4S (B side)
IA - 186.8V
OA - 149.9V
bA - OV
IB - 0V
OB - 92.2V
bB - 149.9V

I think that everything is back to normal. Thanks again for your help!