CBM PET 8296-D KEYBOARD PROBLEMS

[Desperado]

Since you have BASIC available, write a little BASIC program to POKE known characters into the screen, PEEK the values back and compare the value read with what should be there. Put it in a loop and see if it detects any anomalies. If no anomaly’s are detected, it is not the video RAM or buffers, so must be within the later logic generating the video stream.

Dave

Where i can find this basic program please?

 

[daver2]

You have to write it yourself...

Dave

 

[Desperado]

You have to write it yourself...

Dave

Ok thanks
I'll do this next time...now i d like repair my Vectrex if you can help me

 

[daver2]

Try the following. It may need tweaking a bit though...

100 REM Start of video RAM.
110 F = 32768
120 REM End of video RAM.
130 L = F + 2048
140 REM Store character to screen.
150 FOR S = F TO L
160 C = S AND 255
170 POKE S,C
180 NEXT S
200 REM Check screen contents.
210 FOR S = F TO L
220 C = S AND 255
230 X = PEEK( S)
240 IF C <> S THEN GOTO 300
250 NEXT S
260 GOTO 210
300 REM Error report
310 PRINT “Error”, S, C, X
320 STOP

This little program fills the screen with sequential characters and then reads them back and checks them in a loop.

If there is a disparity, the program displays the address, expected character and read character and stops.

See if this program detects anything first. If not, we can modify it to check for faults in the video circuit.

Dave

 

[Desperado]

Wow! Great!
Thanks so much! Today i tryied testing two 4164 ic rams and seems better!
Tomorrow i ll try this BASIC program
Thanks so much!