Re: Testing Galagas

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At 10:36 AM 16/06/2002 -0400, Kev wrote:
>...
> >*Weird problems are sometimes traceable by momentarily shorting circuits to
> >ground on the video board that use resistor pull-ups, the control ICs do
> >not have strong pull-ups (otherwise they would not need the resistors) and
> >you can learn a lot of how the images are built this way. Interesting
> >watching lines appear, characters vanish, stars scroll sideways....
>
>
>Is there some method to this madness?

Yup, by shorting various pull-up lines to Vss momentarily you can often
identify the area of the board where non-rebootable video errors occur. In
other words, things that don't trip the watchdog reset. Fun, and shows how
different Video RAM are used to build the images...not quite what I
expected while poking around...

> >*The horizontal delay timing is CRITICAL and if you are getting RAM errors
> >but the RAM is good, then check the 220pf cap on the delay circuit...
> >
> >That's all for today. But I did get in my Z80QT pod and boy that one is
> >FAST on the RAM tests! A couple of seconds to verify a 1k block instead of
> >a minute or two (short test). What a difference to troubleshooting time!
> >
>
>Sure rub it in! ;-)

Don't be jealous, I'm thinking of building an upgrade for standard Z80
pods...I have a couple of guys who like designing circuit boards on tap at
my shop now, so things might actually start happening!

>Thanks for the tips!
>
>Kev

You guys are welcome!

John :-#)#

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Received on Sun Jun 16 11:47:35 2002