Got a rygar that's running but with graphic glitches as seen in this thread:
https://www.ukvac.com/forum/threads/pcb-repair.85201/#post-587714
Started with the four LS153s that mix the various video signals at 9C,9D,9E and 9F but they checked out as working but noticed inactivity on some of the inputs.
Wasn't sure which inputs were text (as it appears that corruption is bad text all over the screen) so I used my video probe and found the VDAT inputs were producing the text.
Found this was generated from the rom at 8K. Checked the rom and that was fine and fortunately the ram was socketed so swapped with known good but that made no difference either.
I next used my scope to check the addressing on the rom and found A13 and A14 were inactive.
This was fed from an LS174 at 9J. This checked out as inactive but OK as far as the slice could tell.
The inputs came from another LS174 at 9K and that one tested bad. Piggybacked it and all graphics are now fine so I'll be replacing that one.
Board is also reported to be crashing after a time so will soak test it and see if I can find out what is causing that.
https://www.ukvac.com/forum/threads/pcb-repair.85201/#post-587714
Started with the four LS153s that mix the various video signals at 9C,9D,9E and 9F but they checked out as working but noticed inactivity on some of the inputs.
Wasn't sure which inputs were text (as it appears that corruption is bad text all over the screen) so I used my video probe and found the VDAT inputs were producing the text.
Found this was generated from the rom at 8K. Checked the rom and that was fine and fortunately the ram was socketed so swapped with known good but that made no difference either.
I next used my scope to check the addressing on the rom and found A13 and A14 were inactive.
This was fed from an LS174 at 9J. This checked out as inactive but OK as far as the slice could tell.
The inputs came from another LS174 at 9K and that one tested bad. Piggybacked it and all graphics are now fine so I'll be replacing that one.
Board is also reported to be crashing after a time so will soak test it and see if I can find out what is causing that.


