C4S Board Voltage Fail

hughmann · 1773

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Offline hughmann

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on: December 21, 2023, 04:53:34 AM
Finished assembly of the Eros 2.0 and all voltage and resistance tests pass with the exception of 4 terminals on the C4S board.
TERMINALS
OA 217 volts
OC  54 volts
OKA 60 volts
OKC  0 volts

All LEDs light up.
Removed C4S board and reflowed all solder points on "A" side of board and checked for solder bridging.  Remounted board and rechecked voltages.  OA, OC, OKA, OKC still not within spec.
Any ideas would be appreciated.



Offline Paul Birkeland

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Reply #1 on: December 21, 2023, 05:31:40 AM
With the board removed, what is the DC resistance between pins 2 and 3 on the EF86 socket on the side giving you trouble?  Can you also post a picture of the bottom soldering on the C4S board?  Does the EF-86 on the troubled side get warm?

Paul "PB" Birkeland

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Offline hughmann

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Reply #2 on: December 22, 2023, 06:29:22 AM
Paul
 Thanks for the quick reply. With board removed DC resistance on pin 2 was .889 and dropping, pin 3 was over limit. Not much warmth on EF86 but elements are lit up within.



Offline Paul Birkeland

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Reply #3 on: December 22, 2023, 09:48:11 AM
You may have a solder bridge between two pins on the 2N2222 transistor on the side where you're getting 0V.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline hughmann

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Reply #4 on: December 22, 2023, 11:31:37 AM
Paul
I cleaned up the area around the 2n2222 transistor, reinstalled the board retested and the incorrect voltages are still present. Since Christmas is just around the corner, I suggest a break, and come back to this sometime next week. Do you agree?



Offline Paul Birkeland

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Reply #5 on: December 22, 2023, 11:34:18 AM
Sure, that sounds good.  We see this exact problem fairly commonly, and it can have causes like a short between pins 2/3 or 7/8 on the EF86 socket, problems with the wiring to pins 4/5 not allowing the EF86 to heat (glow), or shorts on the C4S board causing the 0V to appear where you should see 1.5V.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline hughmann

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Reply #6 on: December 22, 2023, 12:01:01 PM
Thanks for your time and patience Paul.
Have a good Christmas.



Offline hughmann

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Reply #7 on: December 28, 2023, 04:07:12 AM
Bump.



Offline hughmann

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Reply #8 on: January 08, 2024, 08:21:11 AM
Paul
 I misread your request in reply #1 resulting in incorrect readings. With the board removed, power off, pin 2 reads 0, pin 3 reads 0. Hope this helps.



Offline Paul Birkeland

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Reply #9 on: January 09, 2024, 06:43:24 AM
This needs to be resolved.  Pins 2 and 7 are shield pins and are tied to the chassis so they should read 0 ohms.  Pins 3/8 are cathode/screen and should be OL with no connection to the PC board.  Just to double check, you can also pop off one leg of the big 10,000uF cap that sits there as well just to be sure that isn't throwing off your meter.

Paul "PB" Birkeland

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Offline hughmann

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Reply #10 on: January 09, 2024, 08:36:10 AM
Popped one leg of the cap off and tested pin 3. It initially read 0 ohms but when I moved the tube slightly the reading was jumping all over including OL. Pins 2/7 still read 0 ohms.



Offline Paul Birkeland

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Reply #11 on: January 09, 2024, 09:28:50 AM
Yeah so whatever is in the socket that's causing that intermittent zero is your issue.  Also be aware that the two 0 ohm jumpers need to not be touching each other for this reading to be correct.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline hughmann

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Reply #12 on: January 09, 2024, 09:56:48 AM
Switched EF86 left to right, right to left, pin 3 still at 0 ohm. Should I replace 0 ohm jumpers?



Offline Paul Birkeland

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Reply #13 on: January 09, 2024, 10:04:10 AM
The 0 ohm jumpers connect pins 3 to 8 and 2 to 7.  The problem that you have is that either bare leads of those jumpers are touching or there's some gunk in your socket that's causing either pin 2 to touch pin 3 or pin 7 to touch pin 8.  A failed jumper can't cause this.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline hughmann

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Reply #14 on: January 09, 2024, 11:31:21 AM
Cleaned socket with contact cleaner and paper clip. Pin 3 and 8 read ol with EF 86 tube removed, pin 3 and 8 read .003 ohm with EF 86 installed. Bare leads of jumpers are not touching.