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

[John Robertson]

On 06/30/2014 7:00 PM, William Stillwell wrote:
> 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

Hi William,

Do you mind posting a short copy of your Atari Superman/Hercules 
solution here so it can be found in a search?

Thanks,

John :-#)#
>
> -----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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