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December 07, 2021, 11:15:43 AM

Author Topic: Issue with A Side C4S Board A [resolved]  (Read 1131 times)

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Online Paul Birkeland

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Re: Issue with A Side C4S Board A
« 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

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Offline giggsy

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Re: Issue with A Side C4S Board A
« 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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Re: Issue with A Side C4S Board A
« Reply #17 on: June 30, 2021, 04:33:18 AM »
OB reading is only 102v
KREG is 7.27v

Online Paul Birkeland

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Re: Issue with A Side C4S Board A
« 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

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Offline giggsy

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Re: Issue with A Side C4S Board A
« 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.

Online Paul Birkeland

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Re: Issue with A Side C4S Board A
« 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

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Offline giggsy

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Re: Issue with A Side C4S Board A
« 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.

Online Paul Birkeland

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Re: Issue with A Side C4S Board A
« 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

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Offline giggsy

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Re: Issue with A Side C4S Board A [resolved]
« 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.