28S Advice Needed
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06-18-2021, 07:08 PM
(This post was last modified: 06-18-2021 07:20 PM by twoweims.)
Post: #1
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28S Advice Needed
I was recently given an HP-28S that looks to be in absolutely new condition. No battery compartment corrosion, no broken parts, the leather pouch shows no signs of wear. It powers on and I am able to adjust the screen contrast but there is no display.
The [ON] [<] Test does print numbers on the IR Printer, but the test message says "2 Fail". Is this something that is repairable? EDIT: If it is a lost cause, it is worth noting that the 28S leather pouch will hold a DM42 and a DM41X at the same time. My Collection: 55, 67T, 25PLP, 34C, 15C, 16C, 41CV, 41CX, 41-CL, DM41X, DM42, 42S, 48G, 71B, 75C, 95LX, HP-150, Portable+, HP-86, Integral PC. |
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06-19-2021, 06:08 PM
Post: #2
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RE: 28S Advice Needed
Hello,
Normally during the [ON][ < ] loops indefinitely beeping and displaying active pixels animation and printing 200000 30000 400000 repeatedly on the printer. If it stop on an error, at least a chance a bit is still alive ! I suppose you adjust contrast by pressing simultaneously [ON][ +] or [ON][ - ] ? Did you try any soft system restart using [ON][ ^] or the high ends total reset [ON][INS][ > ] ? |
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06-19-2021, 06:25 PM
Post: #3
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RE: 28S Advice Needed
(06-19-2021 06:08 PM)C.Ret Wrote: Hello, This is exactly what happens. (06-19-2021 06:08 PM)C.Ret Wrote: If it stop on an error, at least a chance a bit is still alive ! It does not stop on the error. It displays "2 Fail" and then repeats the test. (06-19-2021 06:08 PM)C.Ret Wrote: I suppose you adjust contrast by pressing simultaneously [ON][ +] or [ON][ - ] ? Yes. And this does adjust the screen contrast. (06-19-2021 06:08 PM)C.Ret Wrote: Did you try any soft system restart using [ON][ ^] or the high ends total reset [ON][INS][ > ] ? Yes. I tried both of them. My question is , What does the "2 Fail" message indicate, specifically? The manual just says if there is a number followed by "Fail" that I should send it in for service. Obviously, this is no longer possible. I will try to disassemble and repair if "2 Fail" indicates something that can actually be repaired. My Collection: 55, 67T, 25PLP, 34C, 15C, 16C, 41CV, 41CX, 41-CL, DM41X, DM42, 42S, 48G, 71B, 75C, 95LX, HP-150, Portable+, HP-86, Integral PC. |
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06-19-2021, 06:46 PM
Post: #4
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RE: 28S Advice Needed
Normally the reset should have restored the display. this is bad news
The HP-28C / S were not designed to be repaired, they cannot be dismantled without damage since it is impossible to open them without cutting them in half. If this HP-28S had a beautiful exterior appearance that made it collectable its potential will be lost! Especially since there is very little chance that we can diagnose or repair; these are electronics with a high degree of integration and on a SMD scale. No provision or indication appears inside for a possible intervention, maintenance or repair. |
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06-19-2021, 07:39 PM
(This post was last modified: 06-19-2021 07:48 PM by Steve Simpkin.)
Post: #5
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RE: 28S Advice Needed
Not impossible to repair but not easy.
https://www.google.com/amp/s/www.teawea....alculator/ https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=185173 |
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06-19-2021, 09:48 PM
Post: #6
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RE: 28S Advice Needed
After a very successful label removal, i have found exactly Zero broken heat stakes.
The keys all feel like new. Here's what I know: 1) I know that [ON], [+], and [-] work because I am able to adjust the contrast. 2) The LCD is working since I am able to see all pixels when I darken the contrast. 3) The [ON][ < ] combination works to Initiate the self-test. 4) Something is alive in there because the [ON][ < ] test is sending intelligible data to the printer. 5) The [ON][ ^] and [ON][INS][ > ] resets do not work. 6) The [ON][ < ] Test consistently results in the "2 Fail" Message. Time to drill. Maybe new foam under the flexible contact strip and some Deoxit... I wish I could find out what the "2 Fail" message means... My Collection: 55, 67T, 25PLP, 34C, 15C, 16C, 41CV, 41CX, 41-CL, DM41X, DM42, 42S, 48G, 71B, 75C, 95LX, HP-150, Portable+, HP-86, Integral PC. |
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