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Hi! I recently acquired a Midway SID Cocktail. It boots OK, but sometimes - maybe half the time - either during the attract mode or during gameplay, horizontal lines will appear across the Invaders and clutter up the screen. They actually *seem* to interact with the missles as well.

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I installed a Braze multi kit in part to get the diagnostics and to see whether the ROMs may be suspect, and according to that:
  • RAMs test OK
  • Sometimes on boot (maybe 20% of the time), the BIT test fails. When this occurs, there's a continuous tone that is one of the "thumps". Using the diag menu to play the tones, it appears to the "Thump BIT2" tone.
  • On one boot, I got an INP error as well. Assuming that is "input," maybe indicating a stuck input. I think the leaf switches on the paddles controls need adjusting, they're super touchy.

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I've only observed the graphic glitches in SID but haven't spent a lot of time trying other games from the kit. To be clear, the graphic glitches occurred BEFORE installing the Braze kit, and they persist AFTER. I'm assuming that clears the ROMs as being the culprit.

Sometimes the glitches appear during attract and remain, sometimes they clear after the next attract cycle starts. When playing, sometimes I can play several levels without a problem, other times they appear mid-level early on.

I checked voltages at the motherboard edge connector and got:

+5V = 5.19V
-5V = -5.1V
+12V = 12.5V

But hey, it looks like Earl identified this problem way back in 1981!


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I read that as:
Pastime Pub [maybe?]
Scrambled Picture
What else….
3-31-81 Earl


Any pointers on what to check next? I read a thread that seemed similar where apparently the fix was the chip at A5. Not sure what I should be checking on there. I have a logic probe and a very entry level oscilloscope, but I'm not good enough understanding the schematics to be able to figure out what to be looking for.

How about for the BIT failure? I saw the Joe's Video Games video where they found the 556 timer chip that drives the Thumps was bad. Any tips on testing/verifying that chip or something else in that chain to see why I'm having a problem there?

Would love to take a crack at repairing myself rather than send the boards out, I just need some pointers on what to investigate.

Thanks!
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