Help fixing a dead Donkey Kong Jr Pcb

myPinballs

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Hi,

I have a donkey kong (DJR1-01) 2 stack board that i'm trying to get up and running but am having some problems with no video. Blank screen. The board itself is in nice condition with no rust, hacks or bad traces.

Here is what i have confirmed and checked so far.

- Power good to both boards.
- New game roms installed (5B, 5C, 5E)
- New Z80 installed
- Reset line good and solid
- Clock present
- Z80 appears to be running all address lines pulsing , (except for A15 which is high - possible clue to fault?)
- Data lines all pulsing (D0-D7)
- Z80 NMI pin pulsing.
- RD and WR lines are pulsing
- Other control signals pulsing - busak,busrq,mreq,rfsh

Now here's what is odd, the Chip select signals for the roms are not all pulsing. The one to chip 5B is pulsing but the other 2 are high. Also the select pins for ram chips 3B and 4B are high to. The other 4 rams are pulsing.

As i'm looking at the schematic there is some sort of custom memory address chip at location 4D (3192) which looks like a kind of PAL/GAL type custom logic array, but i can't find any info on this or how to check/replace it.

Does anyone have any thoughts on what this could be and if i'm in the right area with this memory address section, or is there something else that could cause these results?

I can't get anything on screen whatsoever, so assume the program is not running.
 
Check your video out,signals at the edge connector and work backwards until you find some type of signal. You should always have a video out of some sort.
 
Ok i made some progress. If i remove game rom 5C then all rom cs lines pulse and i get a picture (video lines R,G,B all pulse), although its garbage it does confirm other things like the clock, colour data and sync is ok. (attachment 1)

Still trying to work out if this help identify something on the address map

Also get a different type of screen image if just rom 5B installed. I was possibly thinking i may get the 1 UP and L=00 in this case but no a full screen of garbage. (attachment 2)

The roms are new and i've double checked that they verify ok from the images i have. Also the sockets and signals to them all check out ok.
 

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Checked everything and had the oscilloscope on all address, data and cs pins. Can't seem to find any 'logic' based issues. I.e a line stuck high or low or floating Was hoping it was just a dead logic chip somewhere.

The only thing i can think is that something is up with a ram chip and that when the program enters an instruction held in rom 5c the data it is trying to write or read from a certain ram location is messing things up. The problem is i'm not sure how to work out which rom address is being accessed when the issue occurs and more importantly which ram address is at fault. I need a fluke 9010a!
 
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