Voltage Regulator Board Problem [resolved]

Scott AA6U · 290

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Offline Scott AA6U

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on: November 29, 2024, 06:02:04 PM
I am building a Stereomour II and got to the point of checking voltages. When I measured Terminal 7, which is the voltage out from one section of the regulator board and is supposed to be between 170-230vdc, it measures 393vdc. That is the full voltage going into the board so for some reason that half of the board not regulating. The other half of the board, which outputs to Terminal 14 and measures 181vdc, which is correct. The LEDs on the half that is not regulating do not light up, but the LEDs on the working side light. Both Terminal 7 and 14 measure 1.6M ohms to ground (there is no resistance standard in the manual for those terminals). I checked for cold solder joints and solder bridges on the board, but it looks good. All components are in their correct places and oriented correctly.  I know tube troubleshooting, but not solid state.  I did measure some voltages on the board. The collector of Q2A (MJE5731A, the output) seems to be the only thing with a different voltage from the side working correctly. Do I have a bad component?  Please advise because I don't know what to do next since it's not a wiring error.
« Last Edit: November 30, 2024, 01:48:35 PM by Paul Birkeland »



Offline Doc B.

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Reply #1 on: November 30, 2024, 05:13:33 AM
The center pin of that MJE5731A is often not well soldered because the heat sink tab wicks of heat when you solder it. Make sure you see a fillet of solder around center leg, on both sides of the PC board.

Have a look at 34:57 on this video which shows a similar situation -



Dan "Doc B." Schmalle
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Bottlehead Corp.


Offline Scott AA6U

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Reply #2 on: November 30, 2024, 07:44:16 AM
Thanks so much! I touched up the solder connections as you suggested and the voltage is correct now.