Vert Char Sync pulse
Posted: Wed Nov 15, 2023 6:25 am
I have been restoring an R2001C, and I have a problem with the video of the characters not being correct.
The A9 Processor Module, sheet 7, U34, seems to be where I can see the problem, but I believe the problem is before this circuit.
The screen displays a line at the top which looks like the video that should be at the bottom of the screen, the video intermittently shows the correct form, but looking at the signals on A9 sheet 7, the pulse seems too wide on pin 10, and there are three pulses out on pin 12 of IC U34. There are no pulses on pin 9, and only a wide pulse on pin 10.
Instead of a nice ramp for the vertical pulse, there is a flat top, where the video is squished on the display.
I have tried finding the waveforms that would be the Char Gen Reset pulse, but I can't determine how it is derived without any waveforms.
Are the boards from a R2001D swappable with the R2001C? As I have a D that needs work...
The A9 Processor Module, sheet 7, U34, seems to be where I can see the problem, but I believe the problem is before this circuit.
The screen displays a line at the top which looks like the video that should be at the bottom of the screen, the video intermittently shows the correct form, but looking at the signals on A9 sheet 7, the pulse seems too wide on pin 10, and there are three pulses out on pin 12 of IC U34. There are no pulses on pin 9, and only a wide pulse on pin 10.
Instead of a nice ramp for the vertical pulse, there is a flat top, where the video is squished on the display.
I have tried finding the waveforms that would be the Char Gen Reset pulse, but I can't determine how it is derived without any waveforms.
Are the boards from a R2001D swappable with the R2001C? As I have a D that needs work...