RE: Major Havoc help (was: Vectrex on Vector Monitor?)

> Wow, thanks Jess for the great write up! I wasn't looking for answers
> specific
> to Major Havoc, but I think the tips you gave me will definitely help
> me with
> board repair in general. I've got a dead Frogger (blue lines frozen
> on the
> screen) and an R-Type with jail bars in the title graphics, so this
> information
> should give me a start on where to look.
>
Jail Bars on graphics will almost always be:

Bad ROM (or stuck graphics dataline-- check any 74x245's or 74x244's on
the graphics datalines.)
Bad Line buffer RAM (these are usually something like a 2148 or 2149
SRAM chip, 2115's, 2125's, or 21xx parts on older games.)

A bad line buffer RAM will generally affect the entire screen (or an
entire "section" of the screen). Problems with graphics EPROMs or the
graphics bus will often only affect areas of the screen with graphics.
(So a title screen that has "bars" through the graphics probably has
something wrong in the graphics databus, but a title screen with bars
all the way across it [even in "black" areas] probably has a bad line
buffer.)

A logic pulser (signal injector) is very handy for finding this kind of
problem. (Radio Shack used to sell one for about $17, don't know if
they still do...) Even without knowing anything about a board, you can
just put the probe on the datalines of various EPROMs while the game is
running. If the game crashes, it's probably a code EPROM. If you get
"bars" or other graphics distortions on the screen you've probably found
graphics EPROMs. I fix a lot of "stuck" bit/bad EPROMs by doing this to
the "working" lines-- when you get to one that *doesn't* change the
screen that's probably the dead one causing the problem.

(This technique doesn't work on games that grab their graphics data from
the program space and then transfer it to RAM, 'cause yanking the EPROM
datalines low will crash the CPU, even if the data is graphics. It does
work on outputs of graphics RAM quite often though.)

> Another question vector related: I have a WG6100 color XY monitor in
> my Star
> Wars with an LV2000 installed. Has anyone else done this? Has anyone
> noticed
> any difference in display when the Death Star explodes before and
> after the
> LV2000 was installed?
>
I didn't notice any difference in display when I put an LV2000 in, but
the monitor that it's in also hasn't died. (And I'm *really* hard on
that monitor-- it's the test bench for all the SW/ESB kits and all other
color monitor hacks and experiments...)

-Clay
Received on Fri Oct 30 10:59:49 1998