|Re: 41c weak display segments|
Message #5 Posted by Tony Duell on 25 Oct 2005, 8:02 a.m.,
in response to message #4 by deleted
I have had a lot of success in repairing missing segments _in other devices_ by cleaning the zebrastrips. One trivial example. I saw a second-hand Fluke 85 multimeter in a second-hand tool shop. When I tried it, some of the segments were weak, but there. _In the shop_ (with the seller's permission, of course), I openied it up, unclipped the display, cleaned the edges of the display on my shirt (!), put it back, and it was fine. I did not attempt to clean the PCB there and then, as I was worried about static damage to the IC. The seller took \pounds 10.00 off the price anyway, since there was a possible fault...
I always intended to clean it properly when it failed again. But it's been fine for well over a year.
I cured one Voyager (original series, with the seperate logic module on the flexible PCB) by taking it apart and cleaning it. Another one did have a defective R2D2 chip, though.
I will admit I have never taken a fullnut HP41 display, but unless I can find good evidence that taking one apart _will_ ruin it, I would give it a go if other cures failed. Yes, I'd power down for a long time first (this is documented in Wlodek's book which every HP41 hacker should have read). Yes, I'd resolder the connections to the keyboard PCB (I've had dry joints there). But I would not assume that taking the unit apart would necessarily ruin it.
After all, the HP manual does give an official procedure for doing this. And my experience of all service manuals is that they err on the side of caution. I've had considerable success with dismantling and repairing modules that the official manuals (HP and others) regarded as not field repairable. On the other hand, there are some things that are almost impossible to repair in the field (hard disk HDAs and dot matrix printheads being examples of things I wouldn't take apart unless there was really no alternative, and with the assumption that I probably wouldn't get them going again).
Which brings me back to my original question. If there is something odd about this display where dismantling it will do serious damage, then I would like to know about it. If there is nothing known like that, I probably will take an old 41CV (the most common 41 in my experience, I have a few with cracked posts, etc) apart and see how I get on. I'll report here anything that I find out.