Arcade PCB problems, couple of onscreen graphic problems.. night driver

[phreak97]

Hi everyone.
I have a Night driver cab, and it's fully playable, but theres always been a random small white rectangle on the bottom right of the screen, and theres no gear or difficulty shown onscreen.
i thought it was probably normal, perhaps something youre meant to stretch off the bottom of the screen.. but looking at this screenshot, it shows the rectangle is meant to be behind the paper car to light it up..
http://www.klov.com/images/11/1181242141102.png

and theres gear and difficulty onscreen too..

i have no idea where to start with figuring this problem out..

[ken_cinder]

Holy crap ancient batman!

I'd bet on it being all located in one screen layer, and located in the same chip........thus that being your culprit.Everything in that lower section of screen is missing if I'm understanding right?
Good luck finding any service docs on that thing though....wow

You'll probably have to do what I need to with my boards I have bad background layers in, and probe until you find the problem.

[phreak97]

i have a pdf manual with full schematics and a heap of troubleshooting info.. i havnt had a good look through it yet, but i'd say it has the required information in it.. its just really difficult to work with a pdf that big which looks like it's a photocopy of a photocopied photocopy..
would posting a photo of the pcb help at all? probably not i'm guessing..
good thing is though, theres only about three custom ics and a tonne of off the shelf ones, so hopefully a replacement will be pretty easy if it's a dead ic.

[phreak97]

ok, i know more about it now, but it still isnt fixed.

the line of text at the bottom showing level, gear, etc was added for mame, it doesnt exist on the actual game, since you can just look at the control panel and see what position everything is in.

the only thing that is missing is the white rectangle ("backlight") that goes behind the paper car stuck on the screen to light it up. it is too small and in the wrong place.

the rectangle is drawn using an and gate with a bunch of inputs (it's a nand gate with an inverter after it.. part availability i guess) which when outputting high sticks 5v through a resistor straight into the video input to the monitor. the inputs to the and gate are coming from the video section (some go through other gates before the big and gate), theres screen position lines there which go to it.. it makes sense if you look at the schematic.

it's odd, in my head the system is simple, but when i look at how they did it, it seems complex. i think i could probably come up with a functional alternative circuit, but i want it restored to original..

if anyone is interested in helping ill post a photo of the screen, so you can see what box is being drawn. i reckon you could figure out what line is not doing it's thing correctly just with the schematic and the backlight's fault position. something must be functioning incorrectly, or been wired incorrectly at some point.. if a line was simply cut, it wouldnt draw a box at all, unless it's a line to the other gates before the and gate, which we've (my friend and i) checked, though i might check again to be double sure.

something to note, one of the lines on the schematic is incorrect, it says V and is should be H (or the other way around, i forget) i think it's a 32V line, but if youre good enouh at digital systems to help me, youll probably be able to figure that out for yourself.

i'd LOVE some help here..