Gottlieb Count-Down (Gottlieb, 1979) System 1 Power issue

pinball_fan97 · Feb 7, 2019

I have a Gottlieb Countdown that's been sitting for years with power issues. Fuses all check out fine. One of the Bridge Rectifiers shows .635 and .630 during diode test which seems to be out of range of .4 to .6. I'm only getting 68.3 VAC between pins 6 and 7 at the input to the power board. Pins 2 and 5 are getting 10.9 VAC short of the 14 and 11.5 expected. Pin 1 is getting 13.3 and pin 4 13.3.

I'm assuming something in the bottom board (in the cabinet) is the cause of my issue as I'm not getting the correct voltage to the power board.. Question is, would the Bridge Rectifier be at fault or one of the transformers be the cause? The youtube videos out there are great for testing but normally the testing is done on known good machines and there isn't much discussion on what is at fault should the testing prove faults. Should I start by replacing the Bridge Rectifier?

Any advice would be greatly appreciated. Thanks.

pinballdaveh · Feb 11, 2019

With the 2 output jacks disconnected from the power supply, measure and record the dc output voltages. The dc voltages should be 4,5,8,-12,42, and 60.

pinball_fan97 · Feb 12, 2019

Thanks for the reply. With the outputs on the power board disconnected I get the following DC voltage readings:

Output pins on top going out to CPU .8, .8 on the 2 pins to the left (should be 5 volts and -12.1 volts on the pin to the far right which sounds about right.

Output pins on the right going to the score displays:
top pin 13 volts, expected 60 volts.
2nd pin 0 volts, expected 42 volts.

Bottom 2 pins .1, expected 4 volts
7.7, expected 8

I'm guessing still that something is bad in the cabinet. Is a reading of .630 and .635 withing range for the one Bridge Rectifier? I've seen good range quoted as between .4 and .6.

pinballdaveh · Feb 12, 2019

I would suggest that both of the bridges on the inside board should be changed because of their age. It also sounds like thereâ€™s power supply issues as well because of many low voltages. Repairing and replacing the parts needed on the power supply isnâ€™t for everyone. Replacing it may be a better option if its the original power supply.