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June 23, 2017, 10:53:11 pm

Author Topic: One side out  (Read 387 times)

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Offline pjnestor

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One side out
« on: June 11, 2017, 02:27:16 pm »
Hi,

I've been using an SEX v 2.1 with a C4s upgrade for several years and it has been working without any trouble.  Recently, the volume on one side dropped off a lot.  Its barely audible.  Switching inputs, speakers and tubes made no difference.

Voltages on the C4s board 0A 354, 1A 67, and 0B 288, 1B 308
A5 is 67, A6 2.2, B5 290, B6 9.4.  The LEDs on 1 side of the board are not lit.

Any suggestions on how to fix it?  I suspect that the C4s is the trouble, is that correct?

Thanks,
Pat


Offline Mordicai

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Re: One side out
« Reply #1 on: June 11, 2017, 06:14:26 pm »
Have you reflowed the connections on the C4S board ?

Offline Caucasian Blackplate

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Re: One side out
« Reply #2 on: June 12, 2017, 12:44:25 pm »
Voltages on the C4s board 0A 354, 1A 67, and 0B 288, 1B 308
A5 is 67, A6 2.2, B5 290, B6 9.4.  The LEDs on 1 side of the board are not lit.
These are pretty tough to read, and I think some are backwards.  Can you check that my list is a correct interpretation?

IA: 354
OA: 67
IB: 308
OB: 288
B5: 290V
B6: 9.4V

If this is the case, your C4S feeding the B side is basically shorted closed and acting as a piece of wire.  I would imagine that seeing some photos of the build could be very helpful in this instance!

-PB


Paul "PB" Birkeland

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Offline pjnestor

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Re: One side out
« Reply #3 on: June 14, 2017, 03:00:16 pm »
Sorry about the format for the voltages, but your list is correct. I have pictures of the board.  Are other area helpful?

Offline JeffYoung

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Re: One side out
« Reply #4 on: June 16, 2017, 05:51:09 am »
Perhaps it's a short between ground (the screw and star washer) and the Y+ pad?  (See arrow in attached photo.)

Offline fullheadofnothing

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Re: One side out
« Reply #5 on: June 16, 2017, 07:34:59 am »
That screw goes into a nylon washer, and therefore is not connected to anything. Also it's on the A side of the board, and it's the B side that has the issue.

On the B side, the soldering of D2 looks sketchy. There is solder in a hole that isn't supposed to have anything attached to it (b/t the 499Ω resistor and Y+). Is that an errant blob, or a connection to something? Pictures of the underside would be helpful.
Joshua Harris

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Offline pjnestor

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Re: One side out
« Reply #6 on: June 16, 2017, 03:42:24 pm »
I flipped the board around a to b and the quiet channel switched sides.  I reflowed all the connections.  No difference.

Offline fullheadofnothing

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Re: One side out
« Reply #7 on: June 16, 2017, 08:09:52 pm »
Does the issue follow the tube?
Joshua Harris

I Write the Manuals That Make The Whole World Sing
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Offline Caucasian Blackplate

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Re: One side out
« Reply #8 on: June 20, 2017, 09:50:10 am »
I would reflow all those joints on the bottom of the PC board.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man