HP Forum Archive 03

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HP41 Strange Behaviour Message #1 Posted by John Robinson on 26 June 2000, 9:49 p.m. I have a 41CX (Fullnut) I brought back from the dead, but it has one remaining curious problem. It does not display any alpha characters properly, infact it doesn't seem to display an non-numeric characters properly. This pretty much makes the calc unusable. To elaborate, pressing '-' displays '-' on every digit, likewise for "+", "/" and "*". Press any function key, "XEQ" say, and the screen is full of very stange characters, but the three digits where "XEQ" would be displayed are different. I know this is not a logic board problem, as I have tried two boards, nor a logic board to keyboard connector problem, as I have tried several of these. It may just be case pressure, as the screw posts are cracked, but seem to hold OK, so I am suspecting the display drivers. Any one else seen this one ?. Thanks - John.

Re: HP41 Strange Behaviour Message #2 Posted by Viktor Toth on 26 June 2000, 10:11 p.m., in response to message #1 by John Robinson John, My first guess would be a bad display contact. Multiplexed LCD displays do all kinds of weird things when proper contact is not made; it's not like LED/VFD displays where a digit or a segment neatly goes out, it's often the whole display that goes nuts, with seemingly insane crosstalk between digits and segments and other unusual behavior. Viktor

Re: HP41 Strange Behaviour Message #3 Posted by John Robinson on 27 June 2000, 2:15 a.m., in response to message #2 by Viktor Toth Viktor, Do you mean contact between the keyboard PCB and the display PCB, or the display PCB and display glass ?. The reason I ask, is that I resoldered all connections between the keyboard PCB and display PCB, and made no difference, although I did only solder the keyboard PCB connection ends. Thanks - John

Re: HP41 Strange Behaviour Message #4 Posted by Viktor Toth on 27 June 2000, 3:33 a.m., in response to message #3 by John Robinson John, I mean the contacts between the display PCB and the display glass itself. I admit I never actually took an HP-41 apart to the point where I'd have removed the display, so I am only guessing here that the display contacts are some kind of pressure contacts, like in many other calculators. If I'm wrong, sorry for wasting your time. Viktor

Re: HP41 Strange Behaviour Message #5 Posted by Steve on 27 June 2000, 10:04 a.m., in response to message #4 by Viktor Toth Check the connections at the display end. There are about 9 wires (quite stiff) that connect to the display. They are so stiff that they can breag the pad away from the board. Using a loupe, look at wach one carefully and nudge the wire with a match (or slightly lever it). If the contact at the display end moves, one of three things has happened: 1) the wire has broken free of the solder joint. This is the simplest, just solder it back on again. 2) the wire is still soldered to the pad, but the pad has lifted from the board -- the track is NOT broken. This is almost as simple, use a small dab of nail polish (what! you don't wear nail polish?) on it to hold everything together and prevent the track from breaking. 3) the wire and the pad have seperated from the board, breaking the track. This is a bit more complex because you need to solder to whatever part of the track remains, and reinforce it with nail polish. This may not be the cause of the fault, but it's worth checking. Typically if fault #1 has happened, some twisting of the case (or even pressure on the ON/USER, or PRGM/ALPHA bars) will change the behaviour.

Re: HP48 gx program transfer. Message #6 Posted by stuart Sprott on 3 Aug 2000, 8:30 a.m., in response to message #4 by Viktor Toth I have written many programs and have had no problem transfering from calculator to calculator. I have sent programs over the internet. Some times this works and sometimes not. I had come to the conclusion that a binary transfer would be preferable to ascii. This seems to be faster and less error in transmission occurs. The last person I sent this to could not get it to work. He suggested that since I am using a mac and he is using a ordinary computer; this may be the problem. I have checked this out by sending a HP program file from my mac to the windows PC at work. This works fine. Can any one shed any light on this problem ?

Re: HP41 Strange Behaviour Message #7 Posted by Erik Wahlin on 4 July 2000, 12:47 a.m., in response to message #1 by John Robinson Hi John, I have had similar display problems with a HP-41C. The problem is usually the metal connectors to the back of the LCD display, or the contacts themselves in side the display. If you find that it is not the metal contact from the main keyboard, try unsoldering the display and removing it. Next pull the two metal clips that hold the LCD to the glass away from the display. There are two silicon rubber contacts on each side. Make sure that there is no dirt on these. Next, I crimped the metal contacts slightly to give them more spring tension and reinstalled the clips. The display worked after that, so there must have been a bad contact. Please don't blame me if the display becomes damaged., As you know, these parts are very delicate.

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