Space invaders garbage on screen

racer2e

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Hi, I just picked up a midway space invaders that has garbage on the screen. Can anybody point me in the right direction? Where would you start?
Jayme
 

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Looks like your reset circuit isn't working.

Edward

+1

I've seen this on several sets of boards only to have them spring to life after fixing the reset portion of the power board.

If you have an oscilloscope, you can SEE it spring high and then go low. I'm not sure if this would show up on a logic probe or not.

No used poking with the main board until you have this known working.

Kerry
 
Try re-seating the daughterboard first...if the edge connector is loose or dirty it'll do the same thing, but yeah its the reset circuit and chances are its the power supply that prob needs attention first.
 
Thanks for the advice guys, I'll dig into it today. I picked this up as a favor for my brother in-law. He always loved this game, so I'm helping get another person hooked on this hobby. I can't decide if that is noble, or evil.
Jayme.
 
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Hi, I just picked up a midway space invaders that has garbage on the screen. Can anybody point me in the right direction? Where would you start?
Jayme

What are them voltages?

+1

Orion3311
Try re-seating the daughterboard first...if the edge connector is loose or dirty it'll do the same thing, but yeah its the reset circuit and chances are its the power supply that prob needs attention first.
 
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Ok, I reseated everything. No change. Checked and adjusted voltages..+12.0 +5.03 and -5.2 and that's as low as it will go. The reset test point shows .03v
 
I removed the reset circuit from the connector on the sound board, and bumped it with +5v but it doesn't even flinch. Ideas?
Jayme
 
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The only way to really test it is to try grounding it - +5v does the exact opposite of what its supposed to do. Basically when powered on it goes high (2.5v or higher) for a split second, then drops low. That way the power supply can settle before the game actually starts up.

You can generally ground it to see if thats the problem (just hold it low) but its recommended that if that indeed does make it work, then the power supply should be fixed properly, which chances are it just needs caps.
 
Well I grounded the reset pin and turned it on, and I get a constant saucer sound, but the screen stays scrambled, and the sound goes away as soon as I remove the ground.
Jayme.
 
Yeah sounds like both the daughterboard needs to be rebuilt, possibly the ps too but if the reset line stays fairly low (under 2v) it might be ok.
 
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