Have a good lunch sir!Excellent.
So, the problem appears to be before the data bus buffer feeding the video RAM.
It's lunch time here, so I will check the schematic after lunch for the next point to probe.
Dave
Do you need always video?OK, I would suggest the following pins next (for comparison purposes).
E7 pins 6 and 13.
Followed by E10 pins 11 and 8 and E10 pins 13 and 6.
Just to confirm - this is with my PETTESTER ROM running isn't it?
Dave
These are same to E7 pin 8 and 11E7 pins 6 and 13.
Also these pins are like previously pinsFollowed by E10 pins 11 and 8 and E10 pins 13 and 6.
Thanks Dave! I try now!Unfortunately, I see what the problem is. The buffers from the CPU data bus through to the buffers on the VIDEO RAM are permanently enabled when the VIDEO RAM is not being read from. As a result, you are seeing all of the activity on the data bus.
The problem is either E7, F7 or F9.
I am less inclined to think it is F9 (the 373 octal latch).
It is more likely to be E7 (244 buffer) or the VIDEO RAM itself at F7.
Is it worth trying our low-value resistor trick to 0V/GND on E7 pin 8 first?
Dave
If i connect E7 pin 8 to Gnd i see correct pettester screen but is stucked on the first page!Is it worth trying our low-value resistor trick to 0V/GND on E7 pin 8 first?
Yes sorry, i don't see flickering chars and i don't see inverse chars!I don't think you will see the correct PETTESTER screen - as you will have no inverse characters on display!