[Techtoolslist] Another midway 8080 and pod (space invaders deluxe) question

[William Stillwell]

I had this same problem on an Atari Hercules/Superman Board, I could
read/write the ram, but when I did a loop random reads would fly across the
screen., turned out to be a clocking issue ( I posted the repair on KLOV and
VillageBBS )

I don't think midway 8080 boards use different speed clocks between ram and
rom read/writes

-----Original Message-----
From: Techtoolslist [mailto:techtoolslist-bounces at flippers.com] On Behalf Of
Rodger Boots
Sent: Monday, June 30, 2014 9:45 PM
To: ayeckley at sierralobo.com; Technical Tools Mail List
Subject: Re: [Techtoolslist] Another midway 8080 and pod (space invaders
deluxe) question

Maybe a sync problem (video system butting heads with processor---wouldn't
happen in normal use).
On Jun 30, 2014 2:12 PM, "Alex Yeckley" <ayeckley at sierralobo.com> wrote:

> > Comes back with 0xFF.  Hit loop and it starts to wander all over
> creation.
>
> From highest to lower probability, based on my experience. YMMV:
>
> 1) bus fight with ROM or I/O bus
> 2) bus transceiver(s) bad
> 3) genuine RAM problem
> 4) I/O control latch problem
> 5) incorrect clock phasing or enable signal threshold between the even and
> odd RAM banks
> 6) other
>
> > Any ideas on why ram would fail this way?
>
> They reportedly could suffer physical damage if the -5V (or was it the
> +12V)
> was not properly supplied.  Not sure the exact failure mechanism was at
the
> die level.
>
> Alex
> ----
> ayeckley at elektronforge.com
> www.elektronforge.com
>
>
>
>
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