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Gottlieab System 1 CPU not booting and my introduction :)
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Brad1023
Hi everyone.
I'm new to Aussie Arcade and very new to pinball as well! My interest starts more with Arcade machines, I built my own Mame Tabletop arcade machine from scratch in my last year of high school, I included a photo of it. It had to have a CRT and replicate games as true to the originals as possible, I had alot of making and playing with it!. Now I'm discovering Pinball, and bought my first machine to restore, A 1979 Gottlieb Countdown. I'm pretty good with electronics, and been playing around with electronics stuff since I was really young :D . But I thought I might find some Pinball enthusiasts who are more experienced on these System 1 machines who could perhaps help me out.
So My CPU on my countdown is not booting correctly, instead of waiting 5 seconds for the displays to light up and hear the Q and T relays pull in, The displays light up and Q/T Relays pull in immediately! While this sounds like a Slam Tilt condition, it can't be, as I have grounded the slam tilt input and made voltage measurements to make sure Z29 Inverter buffer is grounded on the input and +5V at U3 Slam Input.
The other strange thing it does, after very close to 60secs you hear the Q/T relays pull in again and the playfield lights go out, only player 1 and the Credit/Balls-remaining displays are lit and flashing quickly a single 0 and this happens indefinitely until you switch it off. If switched back on again, the same things happen and it's always close to 60Secs when the play field lights go out.
One discovery i made on the CPU board that's bugging me, is making a resistance reading directly between DC ground and the +5V line is a mere 76ohms! surely this can't be right. I have bought another malfunctioning CPU board where this resistance measurement is close to 1Kohms which sounds much more reasonable, could someone with a working System 1 CPU board make a resistance measurement say directly across C16 for me? I have checked all the tantalum caps that go directly across +5V and DC Ground and they are all good, anyone seen this before? My guess is an IC has close to shorted and causing this low resistance.
Any help appreciated, and look forward to talking with you as I enter the world of pinball :)
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