Check the clock circuit, that board has a clock slow down function for accessing ram, and I have seen it cause issues elsewhere, i thought i had a video of it up on my youtube, but i don't ( its for an hercules board ) , bu it was put on a forum post ( http://villagebbs.com/forum/index.php/topic,24850.msg205478.html#msg205478 ) -- a fault 74160 was causing all kinds of random glitches.

William Stillwell


Board Member - Inspiration labs, Inc. a 501c3 organization - Tampa's Premier Maker Space.

Board Member & Co-Founder - Byte Amusement Group // Free Play Florida Arcade & Pinball Show a 501c3 organization

Member of MakerFX - a 501c3 organization - Orlando's Premier Maker Space

Volunteer for The Phoenix - a 501c3 Organization - Providing outreach and events for those who are living a sober lifestyle.  

Former Board Member - West Central Florida Group - a 501c3 Organization. - Providing Emergency Communications across Central Florida.



On Fri, May 28, 2021 at 1:16 PM John Robertson <jrr@flippers.com> wrote:
I don't know if you folks are interested in my headaches, but here is my
latest one.

Working on an Atari Superman  pinball board. ROM, RAM tests are good,
board boots, issue is the feature lamps flicker when turned off.

However I am getting something odd on address 1800-18FFh, it displays
what appears to be the last data bit in the EPROM located at 3800-3FFFh.
I plugged a different EPROM in and got its last data bit too. What is
odd is the EPROM, when reading 1800h shows the Address lines all as low,
but there is the tiniest pulse on /CE(pin 20). I've tried stretching it
out, but it appears to be the smallest resolution of my Tek 100mhz, 2230
storage scope - which I am still learning how to use.

At this point I figure it is a timing issue so will dig further, but I
just thought is was most curious that it didn't matter which address
location 1800-18FFh was chosen, I got what appears to be the last byte
in the EPROM! I have no explanation on how that can happen. I will now
test that by burning a couple of  2716 with only the last byte set, will
try AA and 55 and see what happens...

John :-#)#

--
                  John's Jukes Ltd.
7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
Call (604)872-5757 (Pinballs, Jukes, Video Games)
                  flippers.com
  "Old pinballers never die, they just flip out"


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