Re: 70's Midway board problem

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You can short the outputs of the RAM to common/ground to see if that pair
is the defective one. Simply unplug the "H" ROM and you will get bars on
the screen. flick the slam switch under the coin door lock to shift the
bars. When you short Pin 7 (please verify that is the output!) you will see
a line on the screen that matches that spot. If the line is solid when
you short the line, but dotted when not shorted then one of the two RAMs
are defective.

John :-#)#

At 04:41 PM 23/04/2002 -0700, Matt Rossiter wrote:
>Well, let's take two scenarios just so I understand this.
>
>The ram addresses are between 2000-3FFF
>Say it's reading an error at bit 59 along any address between 2000-3FFF
>
>(..and this is where I'm going to look dumb 'cause I sometimes forget some of
>this)
>
>Would it mean I need to check the rams at bit 4, 5, and 1? or nearby
>multiplexers/buffers?
>
>Bit: 7 6 5 4 3 2 1 0
> 0 0 1 1 0 0 1 0 = 59
>
>Or lets say it finds an error on bit 12 at 20FF. I can't remember what it was
>exactly.
>
>I remember this being easy to troubleshoot. It's intermittant, otherwise I'd
>use the old Midway ram tester.
>
>I'm sorry if I sound so confused. :\
>
>Matt
>
>Kev wrote:
>
> > Fluke questions are probably better asked on the TechToolslist.
> >
> > Bit 12 but what address?
> >
> > Do you have a known good ram that you could piggyback on the suspected bad
> > ram & run the test?
> >
> > > Hi there. You can tell when I'm having a party coming up when I ask all
> > > kinds of 'fixit' questions so I hope nobody minds.
> > >
> > > I'm working on a Midway Double Play (1977) that has an intermittant ram
> > > problem. Using the Fluke 9010a troubleshooter - I'm finding a problem
> > > at bit 12. This is probably a really basic question, but how do I
> > > determine which chips correspond with bit 12?
> > >
> > > There are 16 2107B chips on the board.
> > >
> > >
> > > Bit0 - Bit0
> > > Bit1 - Bit1
> > > Bit2 - Bit2
> > > Bit3 - Bit3
> > > Bit4 - Bit4
> > > Bit5 - Bit5
> > > Bit6 - Bit6
> > > Bit7 - Bit7
> > >
> > > Thanks.
> > >
> > >
> > > Matt
> > >
> > >
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Received on Tue Apr 23 17:15:11 2002