[Techtoolslist] RASTER: FW: Using 8080 pod on Midway 8080 boards (Space Invaders)

[Andrew Welburn]

IIRR There are two resistors on the clock signals coming from the clock 
generator IC for the 8080 ... from memory, they should be 150ohm, but 
you might find different values loaded (taitos are different to schems, 
and had 750's).

You can temporarily short the resistor or change for 100ohm so the clock 
signal goes straight through to the CPU or near enough. the fluke pod 
will then run UUT.

This problem stumped me for months about a decade ago. I just resigned 
myself to the fact you couldn't run uut on 8080 pcbs. I finally came 
across a Taito SI with bad clocks and thats when i noticed the clock 
signal differences before and after the resistors, and the difference 
from the schems.

I will say though, this problem is not really apparent on Midway pcbs, 
rarely do i get UUT run problems, maybe one in the last 30 or so i've 
fixed? I do sometimes get crashing or ram dots appearing, but i tend to 
ignore these because i know this is an artifact of the pod, its not 
worth modding every pcb if i pop a good cpu in and it runs fine. Most of 
the time i dont see it tbh, but ymmv.

I have found a similar case with another game, but i forget what it was 
now, might have even been with an 8085 or something.

Andrew Welburn
http://www.andys-arcade.com

On 19/02/2013 04:12, John Robertson wrote:

> David Shoemaker wrote:

>> The pod has a -1 CPU in it which should be good to 3 mhz the board is a

>> straight 8080a which should be 2mhz.  But I tried it with the CPU from

>> the

>> board just for completeness.  No improvement.  And the pod cpu works

>> fine in

>> game.

>>

>> I have one board that will at least start up partially with the pod,

>> but two

>> others that just error on Run UUT.

>>

>> It is really inconsistent. I think the way the memory system works the

>> fluke

>> ram test will never work (strange timing and sync to get the game board

>> rotation stuff to coordinate access to ram).

>>

>> I have two of these pods, both use the flat ribbon.  I tried subbing a

>> twisted ribbon from an 8085 pod but the pod fails self test (I suspect

>> the

>> ground lead is mucking with something).

>>

>

> I was testing an 8080 board only last year, but didn't get it booting,

> so it is sitting waiting for me to take another go. I can't recall doing

> the "Run" on any of the 8080 boards recently so haven't any better ideas

> at the moment...

>

> Perhaps someone else here has a suggestion?

>

> John :-#)#

>> -----Original Message-----

>> From: techtoolslist-bounces at flippers.com

>> [mailto:techtoolslist-bounces at flippers.com] On Behalf Of John Robertson

>> Sent: Sunday, February 17, 2013 7:23 PM

>> To: techtoolslist at flippers.com

>> Subject: Re: [Techtoolslist] RASTER: FW: Using 8080 pod on Midway 8080

>> boards (Space Invaders)

>>

>> David Shoemaker wrote:

>>> So my mails to tech tools don't appear to be getting through. But

>>> this is a raster game so I will cross the stream.

>>>

>>>

>>>

>>> *From:* David Shoemaker [mailto:davids at oz.net]

>>> *Sent:* Saturday, February 16, 2013 12:20 AM

>>> *To:* 'Technical Tools Mail List'

>>> *Subject:* Using 8080 pod on Midway 8080 boards?

>>>

>>>

>>>

>>> I have a fully working space invaders board which when I hook the pod

>>> up to and do Run UUT doesn't, it starts up and crashes.

>>>

>>>

>>>

>>> Pod passes self test.

>>>

>>>

>>>

>>> Anyone ever done this?

>>>

>>>

>>>

>>> David

>>>

>> Try a faster 8080 CPU in the pod, or try substituting the 8080 from

>> the game

>> in place of the pod CPU. It is possible the CPU is bad or slower than the

>> system can handle.

>>

>> Do you have the flat ribbon cable from the pod to the CPU socket or the

>> twisted pair cable? The twisted pair cable handles noise better and will

>> work in situations when the simple flat cable won't, plus it can be

>> longer

>> as a result.

>>

>> David, I have no idea why this did not show up in TTL - you are

>> subscribed

>> under the same email address as you posted here. I haven't seen any

>> bounces

>> for your email address.

>>

>> John :-#)#

>>

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>>

>

>

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