Measuring Resistors In Circuit

Toys4Boys · 25311

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Offline Paul Birkeland

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Reply #15 on: November 06, 2023, 05:40:55 AM
The 0V at OkC may be what's driving all the issues.  Perhaps consider posting some build photos when you get the chance.  Something like this could easily be caused by a solder bridge on the 2N2222 on that side of the PC board, or you could have no heater voltage on the EF86 on that side (the STP that feeds pins 4/5).

Paul "PB" Birkeland

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Offline Toys4Boys

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Reply #16 on: November 07, 2023, 12:25:20 AM
Any thoughts?


Offline Toys4Boys

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Reply #17 on: November 07, 2023, 07:00:32 AM
Huh, don't know why I didn't see your post. I'll take a look tomorrow and send some pics if the suggestions that you made don't resolve the problem.

Thanks


Offline Toys4Boys

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Reply #18 on: November 08, 2023, 03:48:27 AM
I measured pins 4 & 5, 50-56 volts both left and right sides.


Offline Paul Birkeland

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Reply #19 on: November 08, 2023, 04:43:32 AM
These are the joints I would focus on circled in red, as they don't look well soldered.  In the blue circle, be sure there's no connection between any pair of those pins.

Paul "PB" Birkeland

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Offline Toys4Boys

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Reply #20 on: November 08, 2023, 07:13:09 AM
I have gone thru as you suggested and get the same results. I have examined the solder connections with a magnifying headset and all looks good.


Offline Toys4Boys

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Reply #21 on: November 08, 2023, 10:49:38 AM
Is it isolated to the C4S board?


Offline Paul Birkeland

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Reply #22 on: November 08, 2023, 12:57:06 PM
The front C4S board can be installed inverted, so all the connections are reversed 180 degrees.  Doing this can be useful to see if the problematic voltages swap sides in the amp or stay with one side of the C4S board.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Toys4Boys

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Reply #23 on: November 08, 2023, 01:08:55 PM
Exactly what I was thinking. Project for another day, time for some Celtics Bball.
« Last Edit: November 08, 2023, 01:10:51 PM by Toys4Boys »


Offline Toys4Boys

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Reply #24 on: November 13, 2023, 09:43:13 AM
Apparently the C4S board is fine, flipping the left channel to where the right was and the problem manifests on the left channel of the board now. Does that help pin it down?


Offline Paul Birkeland

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Reply #25 on: November 13, 2023, 09:54:48 AM
I would be extra sure you're getting the appropriate DC voltages at pins 4 and 5 of the 9 pin socket on the problematic side.  Those should be about 50V and 56V.

Paul "PB" Birkeland

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Offline Toys4Boys

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Reply #26 on: November 15, 2023, 02:43:02 AM
One question, could it be a bad tube?


Offline Paul Birkeland

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Reply #27 on: November 15, 2023, 05:36:04 AM
A bad EF86 could be swapped to the other channel, then that 0V at pins 3/8 on the EF86 socket would switch sides.

Paul "PB" Birkeland

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Offline Toys4Boys

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Reply #28 on: November 15, 2023, 06:12:43 AM
Pins 4 & 5 are fine, I will try swapping the tube if you think that is the next step.


Offline Toys4Boys

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Reply #29 on: November 15, 2023, 06:22:58 AM
I don't follow when you say "then that 0V at pins 3/8 on the EF86 socket"?


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