On Wed, Jul 12, 2017 at 03:13 AM, Christian Corti <c...@informatik.uni-stuttgart.de> wrote: > I hope this is also true in your case. According to your picture, the last > column of each character is missing. It could be an issue around the shift > register (e.g. the Display Data register, a latch, cold solder joint, > ...). I just see that I have the following info on my site (didn't > remember that detail ;-) ):
Apologies for the delayed reply and for any messy formatting. I seem to have stopped getting messages from the list, so am building this by replying to an earlier message and copying and pasting from the cctalk archive. It does look like that last column (or possibly two) is missing, doesn't it? Going back to the info on your excellent site, the shift register does seem a good candidate. If we assume that it is parallel in, serial out, then the problem would have to be on the input side, as all the bits pass through every flip flop (ruling them out) and the output is flawed absolutely consistently (ruling out an intermittent fault there). The same reasons militate against a serial input, I think. When I next see the board (hopefully this weekend) I'll try to identify the shift register (which the cross ref on your site will make a lot easier) and look for dry joints under high power magnification. I don't have a complete and working logic analyzer and in any case, the board is not really accessible with a logic probe but TTL is cheap so, even if I don't see anything, a blind faith replacement might be worth considering. I note that it's a 10 bit job and there's nothing in your parts list greater than 8 bits, so I may be looking at more than one IC. Side note: It's probably not a good time to try out my shiny new heat gun that I've never yet used. Maybe save my first go on it for something more replaceable. Of course, a parallel input implies a parallel source, so we still can't rule out an issue with the character ROS. But I do feel like we're making progress and I now have something to do that's more focused than just pulling and reinserting boards until the Gold wears off the pins, so I'm going to call that a step in the right direction. Also, thanks for the additional scans, which I have already downloaded. -- Robert
