----- Original Message ----- From: "Baltissen, GJPAA (Ruud)" <email@example.com> To: <firstname.lastname@example.org> Sent: Thursday, May 19, 2011 9:34 AM Subject: RE: PET 2001 fix Part 3 - RAM/ROM board etc. <snip> >Two things go through my mind: >- The 74100 latches the address to be read by the video circuit. What if >the circuit stops the latching too early (but the rest goes on)? At the >next line the circuit starts with the too early latched address. - What if >the circuit starts one bit too late with clocking the 74107/D5 and 74177 >counters? >My problem: I keep on encountering confusing things, like the combination >at the top of the schematic of the vertical synv and the video on signal. I >only can hope that the above ideas trigger someone elses mind to find a >possible reason for the problem. ---------- I have the same problem; I didn't think it was the '177s, but my head starts to hurt when I try to work through the timing and decoding logic to find what it might be instead. I can't even think of what to look for with a 'scope, but since Philip also has a working PET I've suggested that he compare signals between the two at various points in the video logic; maybe he'll find a difference that will give a clue. An interesting puzzle for better minds than mine though; anyone else have an idea what fault could give the described symptoms: If a line ends with ...ABCDEF, then the next line continues with DDEFGH... instead of GHIJ... mike Message was sent through the cbm-hackers mailing listReceived on 2011-05-19 18:00:12
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