Issue with A Side C4S Board A [resolved]

giggsy · 3137

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Offline Paul Birkeland

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Reply #15 on: June 28, 2021, 04:08:45 PM
OK, now turn the pot up so that same measurement shows 10K instead of 0.  Power up the amp and measure Kreg again and OB.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline giggsy

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Reply #16 on: June 29, 2021, 08:59:14 AM
It got up to 9.6Kohms.
OB reading is only 102v



Offline giggsy

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Reply #17 on: June 30, 2021, 04:33:18 AM
OB reading is only 102v
KREG is 7.27v



Offline Paul Birkeland

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Reply #18 on: June 30, 2021, 06:18:38 AM
I would reflow the MJE5731A and PN2907 joints on that board.  Could you also provide a DC resistance between ground and the center pin of that 9 pin socket?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline giggsy

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Reply #19 on: June 30, 2021, 12:23:03 PM
I am not getting any DC resistance between ground and the center pin.
I am getting 212ohm reading between A3 and center pin.

On the D side I get a 4.9ohm reading between the ground and center pin and 314ohm between D7 and the center pin.



Offline Paul Birkeland

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Reply #20 on: June 30, 2021, 12:32:28 PM
I am not getting any DC resistance between ground and the center pin.

OK, so if your pot is not properly wired or not well grounded, this can throw things off in weird ways and getting 100V at the driver plate regardless of the bias voltage wouldn't be all that surprising. 

With the trim pots all the way up, you should see about 100K between the center post and ground.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline giggsy

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Reply #21 on: June 30, 2021, 01:14:10 PM
Paul, you are a godsend.
I owe you a bottle of whatever you drink.
The ground cable was not attached properly to the trim pot.
I resoldered and now get correct readings across the board.

Now let's hope that's my one screw up.



Offline Paul Birkeland

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Reply #22 on: June 30, 2021, 01:26:25 PM
Well, it did take two pages of posts for me to even consider that! I'm glad you got it all sorted. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline giggsy

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Reply #23 on: July 01, 2021, 12:19:58 PM
I've completed the build and have been listening to the amp for the last hour.
I'm not sure what I was expecting but it sounds wonderful.