Problem Atari Arabian PCB problems (FIXED!)

[RenegadeR]

I got a good looking Atari Arabian with some PCB problems.

So the game plays but displays corrupt graphics, sound is fine.

When I enter the test mode it shows that Rom is ok Ram test shows above that but because of corrupt graphics I can't read it.

Resocketed the roms but no change.

 

[RenegadeR]

So I just checked the 8 roms comparing them to mame arabiana rom and they all check out fine.

When checking the board with my logicprobe, probing the rams I heard a click, like a relais?

And when I checked the screen I saw a lot of garbage on the screen but also saw the enemy sprites moving?!
I did hear the clicking sound a couple of times more and that seemed to affect the game, resetting it and sometimes even flipping the screen upside down?



So the clicking was the coin counter it seems it was stuck somehow, but why would it reset the game and make it act differently.

 

[yorkshire_spam]

Some boards click the counters on start up, not sure about Arabian. If it's clicking "randomly" then it sounds (to me) like an address bus issue as the cpu attempts to address program/data space it's hitting the counter address when it shouldn't. Maybe something in the address decode logic?
Sorry to say I don't think cleaning/re-seating etc is going to fix this PCB - I think it needs to be on a test bench and worked through. It's a nasty multi-cpu + customs design (being a Sun electronics game) but if it was me I'd make up a test harness, get it on the bench and work through the timing/sync circuits, then check the roms/rams in circuit and work from there.

 

[RenegadeR]

Some boards click the counters on start up, not sure about Arabian. If it's clicking "randomly" then it sounds (to me) like an address bus issue as the cpu attempts to address program/data space it's hitting the counter address when it shouldn't. Maybe something in the address decode logic?
Sorry to say I don't think cleaning/re-seating etc is going to fix this PCB - I think it needs to be on a test bench and worked through. It's a nasty multi-cpu + customs design (being a Sun electronics game) but if it was me I'd make up a test harness, get it on the bench and work through the timing/sync circuits, then check the roms/rams in circuit and work from there.

Ok, its strange that the game plays and sounds normal but only graphics are messed up, so does anyone have schematics for this game so I know where I should start to look?

 

[yorkshire_spam]

Ah ok, sorry mis-understood I thought it had "gone bad" when the clicking started.
If it's playing and sound is good then it'll be something in the gfx circuits. Schematics are online
ici

 

[RenegadeR]

Ok thanks a lot, I only had the normal manual and that was not very helpfull.

 

[RenegadeR]

Finally got my portable scope (Zeeweii DSO2512G) in yesterday!

I had been probing around the board with a logic probe for a while but could not find anything really wrong, things pulsed where they needed to pulse so I was quite confused of what could be wrong.

So with the scope it was a lot clearer on IC47 (LS163) there was one pin that had a really low output signal, after I replaced that one the image was better sometimes I could see the background other times garbled but less as before.

Also I noticed one pin on IC66 (LS175) that had a low output, replaced that one and all was ok!

Me and my daughter played the game and I completed Page 4 so after that the game restarts at Page 1 and all graphics where perfect during the playthrough, also monitor is nice and bright, really hard to capture with a phone camera though.