Tech Problem Pacland and Ghost n Goblins

[John Bennett]

[ukvac] Tech Problem Pacland and Ghost n Goblins
Hello.

Can anyone help me. ive got 2 pcbs giving problems.

Ive got a Pacland which poers on with screen of garbage.

And ive got a ghost and goblins that when i switch on i get a screen
of garbage and it resets every second.

can anyone help me.

Thanks

Jason



DATA Imported from archives: originally posted by japo22222 (japo@ntlworld.com)

 

[John Bennett]

[ukvac] Re: Tech Problem Pacland and Ghost n Goblins


DATA Imported from archives: originally posted by mc_35_uk (llantwit@llantwit.screaming.net)

 

[LukeWells]

Re: [ukvac] Re: Tech Problem Pacland and Ghost n Goblins
> GnG same as above then try adjusting (decrease
> then increase ) the +5 voltage, it might suddenly spark up!

Whats the theory behind that one?

Luke

 

[Macro]

RE: [ukvac] Re: Tech Problem Pacland and Ghost n Goblins
some ram chips and eproms work better at slightly different voltages, so
changing it may find the voltage that makes the dodgy eprom start working
again.

I've seen a few boards where you get sparklies on the screen unless you up
the voltage to 5.1v, and have one board that only works at about 4.9v (well,
it did until I changed the eproms - now it works without any change)

 

[LukeWells]

Re: [ukvac] Re: Tech Problem Pacland and Ghost n Goblins
I have boards the same, where you get odd colours or sparklie bits if the
voltage isn't dead on what the board expects.

I never thought about varying the voltage to bring a fussy rom to life.

I assume that this would only work for games in a constant state of reset.
As a game with frozen garbage etc is not going to notice that essential code
that was not available at bootup has suddenly become available.

Why do some boards not do the resetting thing when they are fucked? Is it
because not all boards have watchdog times or does it mean that the cpu is
working sufficiently to execute the watchdog reset commands, and therefore
the fault must lies not in the cpu or code rom but elsewhere?

Luke

> some ram chips and eproms work better at slightly different voltages, so
> changing it may find the voltage that makes the dodgy eprom start working
> again.
>
> I've seen a few boards where you get sparklies on the screen unless you up
> the voltage to 5.1v, and have one board that only works at about 4.9v
(well,
> it did until I changed the eproms - now it works without any change)
>
>

 

[LukeWells]

Re: [ukvac] Re: Tech Problem Pacland and Ghost n Goblins
last one i promise .... I like to learn ...

what actually causes the sparklies and other random SMALL glitches like the
little white lines. Is it like the video ram is missing a beat everynow and
then and whaching up a white pixel here and there instead of the right
pixel?

Luke

 

[MrMish]

Re: [ukvac] Re: Tech Problem Pacland and Ghost n Goblins
> Why do some boards not do the resetting thing when they are fucked? Is it
> because not all boards have watchdog times or does it mean that the cpu is
> working sufficiently to execute the watchdog reset commands, and therefore
> the fault must lies not in the cpu or code rom but elsewhere?
The former, in fact watchdog timers became increasingly
uncommon as boards developed. (Very few manufacturers were
still using them by the end of the 80's).

Bryan