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December 06, 2022, 09:15:57 AM

Author Topic: Right Channel Hum  (Read 868 times)

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Offline thoven0215

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Re: Right Channel Hum
« Reply #15 on: July 03, 2022, 12:06:26 PM »
Other pics

Offline Paul Birkeland

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Re: Right Channel Hum
« Reply #16 on: July 03, 2022, 02:51:52 PM »
Does the 2.49K resistor still measure 2.49K?
Paul "PB" Birkeland

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Offline thoven0215

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Re: Right Channel Hum
« Reply #17 on: July 21, 2022, 01:55:55 PM »
My apologizes for the late response, came back from a trip and had a case of covid. The 2.49 resistor measures at around 0.08 now.

Offline Paul Birkeland

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Re: Right Channel Hum
« Reply #18 on: July 21, 2022, 02:26:42 PM »
I would start by replacing that part and the TL431 on that side as well.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline thoven0215

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Re: Right Channel Hum
« Reply #19 on: July 23, 2022, 01:49:40 PM »
Did you mean the LM431 regulator? I looked at the parts list for the shunt regulator and only saw the LM431 and no TL431.

Offline Paul Birkeland

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Re: Right Channel Hum
« Reply #20 on: July 23, 2022, 03:18:55 PM »
Yes, they are the same part from different manufacturers. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline thoven0215

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Re: Right Channel Hum
« Reply #21 on: July 31, 2022, 11:18:06 AM »
I just want to confirm that my JC2907AN43 is the same as the PN2907A transistor.

Offline Paul Birkeland

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Re: Right Channel Hum
« Reply #22 on: July 31, 2022, 01:22:50 PM »
Correct. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline thoven0215

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Re: Right Channel Hum
« Reply #23 on: August 19, 2022, 09:32:09 AM »
As I was analyzing the B tube socket, I noticed B5 was making contact with B6. Could that have been causing the issue?

Offline Paul Birkeland

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Re: Right Channel Hum
« Reply #24 on: August 21, 2022, 04:35:44 AM »
That will definitely cause some major issues.
Paul "PB" Birkeland

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Offline thoven0215

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Re: Right Channel Hum
« Reply #25 on: August 23, 2022, 09:24:37 AM »
Finally got around to replacing the resistor and regulator and putting the board back in place. Should I go ahead to the voltage check? Here are some pictures of around the board.

Offline Paul Birkeland

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Re: Right Channel Hum
« Reply #26 on: August 23, 2022, 11:23:51 AM »
On the piece of STP in your photo, there's a lot of extra foil hanging around.  If that foil comes into contact with anything other than the chassis, you can run into some real issues. Other than that, yes, you will need to do some voltage measurements.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline thoven0215

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Re: Right Channel Hum
« Reply #27 on: August 23, 2022, 02:37:22 PM »
After cleaning up the foil I measured and found all normal values for IA, OA, KregA, but for IB, OB, and KregB, I got 0 volts dc. I noticed the LEDs on the B side of the board didn't turn on, and the A side of the small pcb also didn't light up.

Offline Paul Birkeland

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Re: Right Channel Hum
« Reply #28 on: August 23, 2022, 04:55:01 PM »
IB is fed from a high voltage node in the power supply.  If that node is pulled to 0V, you will burn up resistors pretty much immediately and you'll know there's a problem.  Since you haven't reported that this happened, you either do not have IB connected to the correct spot, or that wire is broken.
Paul "PB" Birkeland

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Offline thoven0215

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Re: Right Channel Hum
« Reply #29 on: August 24, 2022, 06:48:13 AM »
I checked and my connections seem to be correct. I checked both the IB on the small pcb and the shunt regulator board. I have IB on the small pcb connected to 12L and the IB on the shunt regulator at 34U. I measured the resistors around my shunt regulator board, and some of them do not measure as expected. The 300K ohm 3W resistor on the A side measures at around 200k on the A side.  The 330k ohm 2 Watt resistor measures at 0 on the B side. The 64.9 ohm 1/8 watt resistor measures at around 12 ohms on the B side.