[ukvac] [tech] nintendo popeye
Hi guys, my lame tech questions of the week :-
I have a nintendo popeye pcb on my test bench.
1) The game would not sync, I found the area on the pcb where the sync was
generated and thought I would have a look with my scope, so I clipped the
scope ground lead onto the negative pin of a convenient radial cap and
looked at the sync on the scope .... hmmm it looked fine to me, so I
switched the monitor on and it was synced up. Odd I thought so I
disconnected the scope ground lead and the monitor went mental and started
buzzing (input protection) Connect the scope lead backup and it syncs up
again. Very odd. Must be a bad ground, so I joined a wire from the cap
negative lead to ground, but no joy. Won't sync unless I have the scope lead
clipped on
2) With the scope lead on so I can actually see the screen all I get is a
flashing screen of 0's It flashes every second as though it is watchdogging,
but I checked and the watchdog is not barking. The board has correct clock,
POR and all data and address lines are running on the cpu. There are no
stuck lines on any of the roms/rams and all the chipselects are working. So
going by activity the board appears to be running, but sound and video are
not. Anyone know how these horrid video boards work (I've noticed the bank
of rams that I have never seen before) Any pointers would be greatly
apreciated as I can't seem to find anything that is lacking activity as a
starting point
Thanks
Luke
Hi guys, my lame tech questions of the week :-
I have a nintendo popeye pcb on my test bench.
1) The game would not sync, I found the area on the pcb where the sync was
generated and thought I would have a look with my scope, so I clipped the
scope ground lead onto the negative pin of a convenient radial cap and
looked at the sync on the scope .... hmmm it looked fine to me, so I
switched the monitor on and it was synced up. Odd I thought so I
disconnected the scope ground lead and the monitor went mental and started
buzzing (input protection) Connect the scope lead backup and it syncs up
again. Very odd. Must be a bad ground, so I joined a wire from the cap
negative lead to ground, but no joy. Won't sync unless I have the scope lead
clipped on
2) With the scope lead on so I can actually see the screen all I get is a
flashing screen of 0's It flashes every second as though it is watchdogging,
but I checked and the watchdog is not barking. The board has correct clock,
POR and all data and address lines are running on the cpu. There are no
stuck lines on any of the roms/rams and all the chipselects are working. So
going by activity the board appears to be running, but sound and video are
not. Anyone know how these horrid video boards work (I've noticed the bank
of rams that I have never seen before) Any pointers would be greatly
apreciated as I can't seem to find anything that is lacking activity as a
starting point
Thanks
Luke