Sinistar- Green screen upon startup?

Tupin

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I'm looking at a Sinistar, and the guy who has it says that it powers up to a green screen. Is this as simple as replacing a RAM chip, or is it more complex?
 
not sure about a green screen, but I'm leaning towards it being a main/ROM board connection issue (the ribbon cable) ... I would think a RAM error would generate that never ending rug pattern. I don't have much experience with these though, it could be entirely different than the Defender I've got.
 
I'm looking at a Sinistar, and the guy who has it says that it powers up to a green screen. Is this as simple as replacing a RAM chip, or is it more complex?

Kind of vauge, but could be any number of things. Have him open the coin door and look at the LED on the PCB. Does it flash a series of numbers like 1-3-1 or is it showing a C?
 
Kind of vauge, but could be any number of things. Have him open the coin door and look at the LED on the PCB. Does it flash a series of numbers like 1-3-1 or is it showing a C?

ah yes, well I was right it was different from Defender lol... all the games that came after had the diagnostic #'s on the ROM board. lot easier than the 4 lights Defender had.

another area to consider is voltages... they still running the original power supply in there? could need to be rebuilt. there's some other tidbits about the power headers needing to be reflowed I think, cause they'll create a lot of resistance and burn up connectors and such (much like pinball machines)

those RAMs can't work without +5, +12 and -5 ... strange, I know.
 
Green screens on Williams games indicate that the CPU chip is not executing the power on self test (POST). This can occur for a number of reasons, the primary ones are:
1) bad CPU chip
2) the watchdog circuit is pulsing the RESET line on the CPU
3) the ROM chip at $FF00 is bad or inaccessible (addressing errors)
4) the ribbon cable is bad between the ROM and MPU boards.

I'm sure if I thought about it, I could come up with a few more.

The easiest one to test for is #2. You need to pt a logic probe on Pin36 of the CPU chip. If it is low or pulsing then the CPU chip cannot run.

The next easiest is to replace the CPU with a known good CPU chip.

ken
 
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