HP Forum Archive 15

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HP 21 display repair Message #1 Posted by Harry (Germany) on 1 Oct 2005, 5:58 p.m. Hi, did anyone try to repair a 20series display? I got one display with a non working left digit. This seams to be a corrosion problem. A battery leaked into the whole calculator. Then I have another Display from a 20series wich has one faulty segment in the second digit from the right. Now I am wondering how to make one display for my (otherwise very good) 21 that I just bouth. I think there are two options. One is to cut the two display board in half, glue them togather and reconnect the copper lines. The other one is to try and replace the digit on the corroded board with a singel led, as in the 21 this digit is only used for the "-" in negative numbers. Both of those options seam to be very difficult. Any other suggestions? I will probably end up buying another non working 20series for the display :) Thanks for reading all this nonsense :) Regards, Harry

Re: HP 21 display repair Message #2 Posted by Gerson W. Barbosa on 1 Oct 2005, 8:48 p.m., in response to message #1 by Harry (Germany) Isn't this a 59,5 x 18 mm board with 12 7-segment LED and 20 point connection points for other board? I have one of these in front of me. It was given to me last week by a friend who knows I like these things. There's soldering on three of the connection points (he's a radar technician and like doing experiments - hopefully he hasn't damaged it :-). Anyway, this would cost you ... a post card! E-mail me if interested. Regards, Gerson.

You got mail. NT Message #3 Posted by Harry (Germany) on 2 Oct 2005, 6:16 a.m., in response to message #2 by Gerson W. Barbosa no text

Re: HP 21 display repair Message #4 Posted by David Smith on 2 Oct 2005, 3:27 p.m., in response to message #1 by Harry (Germany) The display module uses chip-on-board technology where the individual LED chips are attached to the board and wire bonded down This makes the LED module like a big integrated circuit chip. You can pretty much forget sawing the thing in half and patching it back together... unless you have a wire bonder, chip bonder, full chip doctor setup, etc... but if you had these you probably would not have asked the question. Best to find a machine with a bad ACT or RAM chip, and salvage the display module.

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