The Aussie Pinball Arcade
Aussie Pinball Forums => Technical Matters => Circuit Board Repair Guides => Topic started by: poho on March 27, 2014, 10:09:13 AM
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Hi Guys,
Was hoping for some pointers. I have a WPC No Good Gofers machine. I turned it on the other day and the screen *mostly* worked. It's like everything around the top left of the screen was either not working or flickery. Over the course of a minute this spread from the top left all the way to the bottom and now the screen displays nothing. I've tested the screen in another machine and I know it works fine. I've discovered that i'm missing +60 from the a/v board. All the other voltages are fine I'm fairly confident that the problem wasnt a fuse as they have all tested ok, and i expect that whatever died, did so over the course about one minute. Now my question: What are the most likely culprits? I've run my multimeter over the back of it, the traces, resistors and diodes seem fine (well the ones that look like they have something to do with +60 on the schematic). I'm thinking its one of the Transistors at Q2 or Q1 - is this a good place to start? Could it be also be a capacitor causing the problem? Which ones would would be most likely?
Cheers guys
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From memory there is a plug with purple wires that is the AC input to the board. There is a connector in the bottom of the cabinet that the 60VAC runs off the transformer. If the head has recently been lowered, it can stress this connector and I have seen it pop out before, giving you no 60VAC. Check that connector.
Other than that, the HV section on the DMD board would need to be rebuilt.
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The 2 pin violet connector is from the 100VAC winding - used to make the -113 and -125
The white wires make the 80 VAC winding, converted to 62 volts, come from the rectangular plug in the cabinet. Pins 5&8
I'd be very surprised if this is anything but a HV problem.
My suggestion - don't just replace 1 component, shotgun it.
I don't normally suggest shotgunning any repairs, but HV problems are the exception. The enemy here is heat. Everything on the board has been exposed to heat. If you replace 1 resistor or diode, you'll be in there replacing another one tomorrow.
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+1 on that John
When you fit the replacement zener diodes make sure you lift them off the board by a few millimeters. it will help with heat dispersion.