TECH: Moon Cresta

[marog_uk]

[ukvac] TECH: Moon Cresta
I've got a problem with a Moon Cresta cocktail twin board set. In normal
game mode the screen flashes between full colour garbage (characters,
graphics, blocks all over the screen) and blank with a frequency of about
2Hz. In test mode I get a single line of the characters
'ABABABABABABABABABA' all they way across the center of the screen.

I tried swapping in some Galaxian roms and just got garbage all over the
screen in both game and test mode (not 100% sure I got the correct roms in
the correct sockets).

Any suggestions?

Cheers,
Steve

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[John Bennett]

Re: [ukvac] TECH: Moon Cresta
Could be one of many things - The blanking you see is the watchdog kicking
in - this is a sign somthing is properly wrong there should be a pad on the
top (main, not the rom board) board to the left hand side - near the
middle - stick a blob of solder on this to stop the watchdog.

Next thing - check the processor is running - have you got 6MHz clock on
pin6 - is there activity on the data lines? - try swapping in another Z80
from a working board.

Next - check the roms - do you have an eprom programmer - if so check them
against romident to ensure that they are OK - make sure they are seated
properly and no pins are bent. - check the data lines have activity. - does
the garbage change when the rom card is removed - if not then the program
isnt running at all.

If youre happy its not the processor or roms - start looking at the ram -
most probably the 2 2114s on the top board, or the 2101s on the bottom.

If after all this its still knacked - its gonna need someone who knows what
their doing looking at it.

Grab a copy of the galaxian trouble shooting guide and use that to try and
see whats going on - but bear in mind, that although moon cresta and
galaxian boards look REALLY similar - there are a few subtle differences -
drop me a line if you need any more help.

Cheers
Gav



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