HP Forum Archive 14

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Dead 41C - Slight Progress!!! Message #1 Posted by Joanne on 28 May 2004, 1:17 p.m. Hi again! The messages seem to have been split up in the list so I put as a new one. I felt so excited about all your comments and suggestions that I decided try the �esoftware�f ones myself before the big step of opening it up. Yes, it does have square corners so it must be �efullnut�f. I shook it very slightly but there isn�ft anything broken off and rattling around inside. I cleaned again the springs/coils and battery contacts. I tried to stretch slightly the coils to make better contacts. Then I tried combinations of backarrow (�©); R/S; backarrow then ENTER then ON, etc as suggested. Something happened!!! If I leave the calculator to sit (with batteries in) for about 30 minutes, then press any of the following keys (but only these specific keys) (ENTER, -, +, �~, �€, 7, 4, 1, 0) the display flashes for a split second a row of @ signs. Each time I press one of the above keys again, it flashes but for less time and much weaker. After about 4 or 5 attempts, nothing happens at all (as if it were dead/turned off). Then I leave it about 30 minutes and the same thing happens again. Does this give anyone a better idea of what might be the problem? You�fve been incredibly supportive so far! Thank you all. Best wishes, Joanne

Re: Dead 41C - Slight Progress!!! Message #2 Posted by Tony Duell on 28 May 2004, 2:22 p.m., in response to message #1 by Joanne This sounds very like bad internal contacts. The Fullnut HP41s consist of 4 main parts -- the 'I/O assembly' (the flexible PCB that connects to the batteries and the module ports ; The keyboard PCB ; The logic PCB (contains the CPU, ROM and RAM memory chips, power supply, etc), and the display. The display is connected by soldered jumpers to the keyboard PCB, the logic PCB and I/O assembly are connected to the keyboard PCB by pressure connectors that are clamped together when the case is assembled. Bad contacts on the latter are common, I have (once) had a bad soldered connection to the display. If you are happy working on delicate, static-sensitive CMOS electronics, then the next thing to do is take it apart and clean the contacts. Remove the battery pack, peel off the feet and undo the screws under them. Lift off the bottom case and the U-shaped 'middle case' (this must go back the right way up!). Then lift off the logic board, noting any washers on top of it (some very early units have 1/4" nuts here). Take off the connector under the logic board. Clean the contacts on the logic board (2 rows), the contacts on the keyboard PCB (2 rows for the logic board, one row for the I/O assembly), the logic board connector, and the I/O assembly's contacts with propan-2-ol (isopropyl alcohol). Put it all back together. Take great care when putting the screws back in. If you crack a post, you will have a lot of work to repair it (and unless the case is properly assembled and clamped, the machine will not be reliable). The best way is to put the screw in the hole, then turn it counterclockwise until you feel it engage, then screw it home. Tighten the screws evenly, do not overtighten. I hope this gets it going again.

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