[Techtoolslist] And another weird test result

[William Stillwell]

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
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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 at 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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