Moon Cresta problem

[John Bennett]

[ukvac] Moon Cresta problem

I have three Moon Cresta boards (2 original) and they all
display random coloured dashes at the right side of the screen
(which is really the top of the screen because it's a vertical game).
This only happens while a game is in progress and it is not very
noticable. Is this normal?

I was thinking that it might be due to crap programming i.e.
writing to VRAM while it is being accessed by the hardware?
It's hard to believe that my three boards have exactly the same
fault. Can anyone shead any light on this?



DATA Imported from archives: originally posted by shepg2002 (lists@ntlworld.com)

 

[John Bennett]

Re: [ukvac] Moon Cresta problem
Hi there

I have an Original Monn Cresta PCB

and that does it as well... have to agree very crap..

Regards

Daz

They were the days



DATA Imported from archives: originally posted by Dazzer (daz@darrenwhitsed.freeserve.co.uk)

 

[John Bennett]

Re: [ukvac] Moon Cresta problem
At 12:41 20/09/2002 +0000, you wrote:

>I have three Moon Cresta boards (2 original) and they all
>display random coloured dashes at the right side of the screen
>(which is really the top of the screen because it's a vertical game).
>This only happens while a game is in progress and it is not very
>noticable. Is this normal?
>
>I was thinking that it might be due to crap programming i.e.
>writing to VRAM while it is being accessed by the hardware?
>It's hard to believe that my three boards have exactly the same
>fault. Can anyone shead any light on this?

yup - all mine do the same - the dashes coincide with stuff on the screen -
crap programming methinks

Cheers
Gav



DATA Imported from archives: originally posted by Gavin Yuill (mingjy@ecu-01.novell.leeds.ac.uk)

 

[P-Man]

Re: [ukvac] Moon Cresta problem
and something that is not emulated in mame, thus, making everyone think
there is somethgin wrogn with their pcb...

also like tapper, tron, defender, joust, robotron.. all have crap on the
peripheries of vision..

Andy

 

[Macro]

RE: [ukvac] Moon Cresta problem
it's all down to the wonderfully weird sprite circuit - it should match
sprites further down the screen

I have had some boards that didn't do it, but not many, it seems to be down
to timing, so if everything was perfectly on time, then it wouldn't happen
(and of course, Mame is perfect ...)

 

[Macro]

RE: [ukvac] Moon Cresta problem
sorry, thinking about it, it's probably a combination of software and the
circuit - updating the sprite registers too late causes it to want to draw
bits of sprite, the more sprites on screen, the more it happens.

I don't think galaxians has the problem, because it updates all the sprite
registers en-masse at the start of the blanking interrupt (besides, it
doesn't often have that number of sprites displayed)

so maybe the board I have that works has a slightly faster clock overall ?

oh, and of course, watch the nice screen glitch on the 'PRESS PLAYER 1' line
after you inserted one credit - thats updating things as it draws then.

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[John Bennett]

[ukvac] Re: Moon Cresta problem



DATA Imported from archives: originally posted by shepg2002 (lists@ntlworld.com)

 

[Macro]

RE: [ukvac] Re: Moon Cresta problem
>So it can be fixed then by hacking the ROMs?

hmm, possibly

>or maybe you have a version of the ROMs where the problem has
>been fixed?

nope, bog standard, it's the version in my multigame

interestingly, mame 'emulates' that the sprites only work in a certain zone,
and the glitches are outside of that zone, so mame could be totally wrong
anyway. (have to plug my pacman daughterboard back on and see if the heads
get chopped off on the top of the maze)

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[John Bennett]

[ukvac] Re: Moon Cresta problem

> interestingly, mame 'emulates' that the sprites only work in a
certain zone,
> and the glitches are outside of that zone, so mame could be
totally wrong
> anyway. (have to plug my pacman daughterboard back on and see if
the heads
> get chopped off on the top of the maze)
>

On my boards the glitches are visible all the way down the right
side of the screen. This includes areas where the sprites go. The
problem is worst in the top right and bottom right corners. Also,
I am not talking about the periphery of the screen. The glitches
cover approx. one third of the screen on the right side. However,
they're not very frequent and very brief. Is this normal?

The glitches don't bother me but they cause problems if I sell
the boards.



DATA Imported from archives: originally posted by shepg2002 (lists@ntlworld.com)

 

[Macro]

RE: [ukvac] Re: Moon Cresta problem
> they're not very frequent and very brief. Is this normal?

yep, I spent about two hours on my first moon cresta trying to track down
the problem, until p-man told me they all did it!

>The glitches don't bother me but they cause problems if I sell the boards.

shouldn't do, since virtually all do it anyway (I think I've had two that
didn't and they were both midway galaxian boards)

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[d-type]

RE: [ukvac] Moon Cresta problem
Try jamming the data lines high or low between the uP and ROMs and back
again.

You might be able to get a dodgy and a good check by shorting either side of
an IC i.e. the input and the output.

Worth a go?

Phil

 

[guddler]

Re: [ukvac] Moon Cresta problem
Found the problem to this in the end BTW. Initially, although what
Phil said didn't sepcifically locate the problem, it got me down the
right lines and enabled me to look in the right place to find it in
the end!

All the chip select circuitry was shot so whatever i read it was
reading the program ram, hence all ram tests passing!!. I replaced 8
ICs last night - i forget exactly which ones, but all were either
157's or 367's. Game now runs with issues.

Not least of which the sound has a permanent horrible screeching noise
that so loud it's unbearable, but also, the picture starts off in
black & white but within about a minute it will "fade in" to colour.
Albeit with no green. Doesn't seem to be the object roms, the video
ram or the colour prom (ie, swapping them with ones off other boards
and they still do the same). Most weird!

I think this board has had a major upset at some point in it's life )

It's certainly turning into a bit of a repair marathon!

Oh well...

Martin.

On 05/06/05, Phillip Eaton <inbox@phillipeaton.com> wrote:
> Try jamming the data lines high or low between the uP and ROMs and back
> again.
>
> You might be able to get a dodgy and a good check by shorting either side
> of
> an IC i.e. the input and the output.
>
> Worth a go?
>
> Phil
>
>
>