Blank screen, Blanking line to output colour proms always enabled. Trace back to 74161 in timing circuit – output stuck, input clock all look OK – replace chip and picture appears.
Blue video only – The video lines are controlled by three transistors near the edge connector, checking these revealed that 2 were not giving any output although inputs were changing. replaced these and full colour restored.
If you put a Mr Do in a normal Jamma cab, then the picture will be upside down. This can be solved many ways, but one is to change the program code – If you wish to use Mr Do in a standard vertical Jamma cab, then you need to Click Here to get the updated images.