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Author Topic: Mainline Voltage Check [resolved]  (Read 98 times)

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Offline jleewitda3

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Mainline Voltage Check [resolved]
« on: April 27, 2021, 07:55:33 PM »
I just finished building my Mainline today and came across an issue as I was going through voltage checks. Here are my readings:

+275V DC on the Power Supply Board (275V): 283.2V
+6.3V DC on the Power Supply Board (55-65V): 9.97V
-6.3V DC on Power Supply Board (50-60V): 3.71V
IA on the A side C4S Board (275V): 281.1V
IA on the B side C4S Board (275V): 281.3V
Breg on both sides of the Regulator Board (220V): 216.2V, 214.6V
-reg on both sides of the Regulator Board (0V): 0.2mV, 0.2mV
Kreg on both sides of the Regulator Board (8-12V): 9.89V, 9.93V

My main concern comes from the +6.3V and -6.3V on the Power Supply Board, as they are way below their expected readings. I've done the resistance checks already, and the 4 LEDs on each of the C4S Board along with the 3 tubes illuminate just fine (within a few seconds). Moreover, as far as I know, everything is wired and soldered properly. Any thoughts on what may be the cause?

Cheers and thanks in advance
« Last Edit: April 28, 2021, 08:02:21 AM by Paul Birkeland »

Offline Toobuzz

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Re: Mainline Voltage Check
« Reply #1 on: April 28, 2021, 03:35:18 AM »
Congrats on the build! I’m no expert, but I just built a ML and had to work through a few issues. Double (triple, quadruple) check your jumper wires on the bottom of the circuit boards. Mistakes can easily be made here as each board is symmetrical.

Online Paul Birkeland

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Re: Mainline Voltage Check
« Reply #2 on: April 28, 2021, 05:47:10 AM »
On the power supply PC board where it says "PT-11 PSU PCB" there is a big carbon film resistor and below that a small zener diode.  Can you measure the voltage across the zener diode?  Is it installed in the correct direction?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline jleewitda3

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Re: Mainline Voltage Check
« Reply #3 on: April 28, 2021, 06:39:27 AM »
Thanks for the help, PB. The zener diode seems to be oriented correctly and reads 3.70V, which is the same as the reading on the -6.3V pin. For reference, my AC mains power reads 124.1V.

Online Paul Birkeland

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Re: Mainline Voltage Check
« Reply #4 on: April 28, 2021, 06:41:59 AM »
Can you post pictures of each 9 pin socket?  I suspect there is debris or some contact between pins that shouldn't be happening that's throwing off that voltage.

I would also pull all 3 tubes and see if the voltages at the 6.3V pads pop up.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline jleewitda3

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Re: Mainline Voltage Check
« Reply #5 on: April 28, 2021, 07:33:16 AM »
Thanks PB! You were on the money regarding contact between the pins. The resistor on A2, although hard to see, was in contact with the A3 pin. The readings are now 58.9V and 52.6V for the +6.3V and -6.3V pins, respectively. I'll redo both resistance and voltage checks and report any other issues.