Gottlieb System 1 Power supply -12 volt and 8 volts out to lunch

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jim43bob
Posts: 5
Joined: Sat Nov 10, 2012 1:23 pm

Gottlieb System 1 Power supply -12 volt and 8 volts out to lunch

Postby jim43bob » Mon Apr 15, 2019 10:56 am

Hi everyone. Working my way through my Genie and having trouble with -12 VDC and +8VDC outputs.
Have changed all electrolytics,LM7912 voltage regulator, all diodes and adjustable pots. Have reflowed all connections.
I'm good on the 42VDC, 60VDC,+5 VDC and +4VDC.
But I'm getting -.86 VDC instead of -12VDC and +16 VDC instead of +8 VDC.
The only things left I can see to change are the two SCR's and the LM723 voltage regulator.
My inputs are good coming in on A2 P1 and I am making sure to use the right ground reference when measuring the voltages.
I even checked to make sure that LM7912(LIC1),PMD-12k-40(Q1) and MJE 340K(Q2) were isolated from ground.
Oh and I did double check the orientations of all the electrolytics and diodes.
I know I can get a new supply from Big Daddy or Great Plains but I've come this far on this one and hate to give up on it!
Any help appreciated!

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sylvain
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Joined: Thu Nov 19, 2009 7:39 am
Location: Ottawa, Ontario

Re: Gottlieb System 1 Power supply -12 volt and 8 volts out to lunch

Postby sylvain » Mon Apr 15, 2019 9:25 pm

Are you measuring the lack of -12V with connector A2P2 removed, or connected?
This is to identify if the issue is still with the power supply, or downstream.
NOTE: Never disconnect or reconnect connectors with power ON, or damage to some components could occur.

For the -12V supply, it should not be too difficult, apart perhaps for the protection circuit's SCR and Zener diode.
- check diodes CR3 & CR4 along with their orientation;
- check C4 1000uF capacitor and its orientation;
- check the 1A SB fuse in the cabinet;
- confirm you measure 14VAC on input A2P1 between pins 3 & 4;
- confirm you measure 14VAC on input A2P1 between pins 3 & 5;

As always for all of us replacing parts on boards: Always double check the work done. And the solder joints.
Confirm that the proper components are at the correct place and orientation, and are good.

UPDATE: Also make sure that A2P1 input connector is not connected backwards.

Good luck!
-Sylvain.
Looking for Bally Star-Jet, Capersville or The Wiggler, Williams Magic City, Grand Lizard, Swords of Fury, 1986 Pinstar Gamatron, and a few others.
Collecting & repairing electro-mechanical and solid state pinball machines with quality and care for over 35 years.
Serious and fun hobby, powerful nostalgia !


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