Display Issues after MPU repair

LanHell

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I got a game a while back with a pretty badly acid damaged Bally AS-2518-35 MPU board. The main ground trace surrounding the board on both sides was nearly gone.

After cleaning it up and sticking in a battery corrosion repair kit, pin headers, and recapping the solenoid board with parts from Great Plains Eletronics, I was able to get the the game booting up and playing normally. However, I'm having an issue with the displays that I haven't seen anyone else mention before.

While the displays seem to be showing the correct info (score, credits, etc.) they seem to be 'strobing' very slowly.

From what I've read, the MPU displays one digit at a time on the displays, but does it at a rate of about 350 times a second which in effect makes the display appear that all numbers are being shown at once.

Mine seems to be going at a much slower rate as the video shows.
http://www.youtube.com/watch?v=y22D6Vfp3xw

Any ideas?
 
Did you replace any of the components in the display interrupt generator circuit? R21, R22, R23, C16 and C17.

The display interrupt generator is basically just a 555 timer. The rate of the timer is set by these resistors and caps. If one was replaced with the incorrect value it could cause this kind of problem. The schematic shows the voltage at the interrupt generator output at 4.5VDC so you could check that but it will be strobing so a frequency counter or oscilloscope would be better.

EDIT: R23 is just a pull up so it's part of the display interrupt generator but won't cause this problem. R21, R22, C16 and C17 definitely could.

EDIT2: This could also be caused by one of the parts mentioned going open or out of spec due to corrosion.
 
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I'm not familiar with the kit you installed.....did you replace J1 on the MPU board and/or the pins inside J1? This is where I would check very closely for damage from the corrosion you repaired.
 
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