Repair service [resolved]

preston.ezell · 8412

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Offline preston.ezell

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Reply #15 on: October 14, 2021, 02:54:31 PM
So it appears that flipping the transistor did not solve my issue. I still have 0 voltage at terminal 1 and 0 voltage at OA


Offline preston.ezell

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Reply #16 on: October 14, 2021, 03:02:21 PM
I checked the resistance of my 150kohm 2W resistors on the small board and the A side resistor is reading a varied amount that doesn’t really go above 25kohms.

This resistor needs replaced, right?


Offline preston.ezell

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Reply #17 on: October 14, 2021, 03:23:06 PM
So I got a stable reading. Seems the a side 150kohm resistor is reading 55kohms max.


Offline preston.ezell

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Reply #18 on: October 14, 2021, 03:31:40 PM
I guess I need replacement parts for my small board. How do I go about ordering these?


Online Paul Birkeland

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Reply #19 on: October 14, 2021, 03:41:04 PM
Woah, slow down a little.  A 55K resistor would actually work fine there. There's also not really a failure mode to kill that part.

In the photos you posted of the build without the C4S board, there is what looks to be some metal material between pin A5 and pin A6.  If those pins touch, you'll get 0V at terminal 1.

Paul "PB" Birkeland

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Offline preston.ezell

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Reply #20 on: October 14, 2021, 03:49:50 PM
I will fix that up and report back


Offline preston.ezell

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Reply #21 on: October 14, 2021, 04:02:45 PM


Offline preston.ezell

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Reply #22 on: October 14, 2021, 04:06:20 PM


Offline preston.ezell

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Reply #23 on: October 14, 2021, 04:13:24 PM
So I have a voltage reading at OB on the large board without the amp being plugged in, is this supposed to be happening?

https://drive.google.com/file/d/1dnbaZ1RjwL-SR0mXSRfe0FVfG6lflLGN/view?usp=drivesdk
« Last Edit: October 14, 2021, 04:15:20 PM by preston.ezell »


Offline preston.ezell

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Reply #24 on: October 14, 2021, 04:55:54 PM
I have 0V at B7 and B8. I’m not sure if I’m supposed to have any.


Online Paul Birkeland

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Reply #25 on: October 15, 2021, 03:52:07 AM
At this point you'd want to focus on the small board not working properly.  You can even unplug the 6080 for now and just run the amp with the 12AU7.

Can you do a DC resistance check between terminal 1 and ground?

Generally when a C4S board fails to function, we see high voltage on the output and resoldering is required.  Seeing 0V on the output is more typical for the output being somehow shorted to ground, which suggests debris or wire ends touching as a cause of the problem.

Paul "PB" Birkeland

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Offline larcenasb

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Reply #26 on: October 15, 2021, 05:55:34 AM
Paul, it's incredible just how knowledgeable you are about virtually every single scenario concerning the circuit and troubleshooting. I mean I know you're a designer lol, but still... Hats off to you for all your help :)

Lowell B.

Online Paul Birkeland

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Reply #27 on: October 15, 2021, 06:02:41 AM
I've just messed up my fair share of builds. 

Paul "PB" Birkeland

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Offline preston.ezell

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Reply #28 on: October 15, 2021, 06:34:11 AM


Offline preston.ezell

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Reply #29 on: October 15, 2021, 06:35:21 AM
34.3k ohms


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