Data East MPU Repair - need inspiration

[pinballmania]

Working through a pile of non working Data East CPUs and hitting a brick wall on this one.

The CPU does not boot correctly.

The 6802 processor, 6264 RAM chip and Game chips are all tested and known good in another board.
All jumpers are correctly set for 1 27c512 eprom.

With a game ROM installed, the 5V LED comes on, PIA on, Blanking OFF as normal, then blanking LED turns on as normal, but PIA flicks on and off, blanking remians ON.
With LEONs test Eprom installed, board enters test mode and PIA light blinks on and off as expected. ALL PIAs test correctly with the correctly cycling outputs. The memory test appears to pass, as it returns to flashing mode after being initiated.
With Data East test eprom installed ( works in another board ), the PIA locks on and nothing else happens.

Any initial thoughts?

Andy

 

[DAFlippers]

I'd check the PIA CSs on scope and logic analyser for LEON and DE Test ROMS.


David

 

[pinballmania]

Thanks David. Have also done that and just rechecked. Have pulled Eprom and now have it in no-op. All the address outputs are cycling as expected. Reinforced I think by Leon test eprom selecting each PIA.

 

[DAFlippers]

I presume it is still not working. If that is the case then go back through CS logic and see if you can spot odd timing on selects. I found some cracked resistor arrays on Sys 11 boards that gave spurious failures so check RA5 and any other that might be in the area.

<Edit> cracked = lost pull ups

 

[DAFlippers]

Did you fix it Andy?

 

[pinballmania]

No. I’ve put it in the less important pile. I’ve fixed up 4 others and have three others to do. It may not get fixed !!