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28S Advice Needed - twoweims - 06-18-2021 07:08 PM
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.
RE: 28S Advice Needed - C.Ret - 06-19-2021 06:08 PM
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][ > ] ?
RE: 28S Advice Needed - twoweims - 06-19-2021 06:25 PM
(06-19-2021 06:08 PM)C.Ret Wrote: Hello,
Normally during the [ON][ < ] loops indefinitely beeping and displaying active pixels animation and printing 200000 30000 400000 repeatedly on the printer.
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.
RE: 28S Advice Needed - C.Ret - 06-19-2021 06:46 PM
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.
RE: 28S Advice Needed - Steve Simpkin - 06-19-2021 07:39 PM
Not impossible to repair but not easy.
https://www.google.com/amp/s/www.teawea.com/open-a-hp-28s-calculator/
https://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv020.cgi?read=185173
RE: 28S Advice Needed - twoweims - 06-19-2021 09:48 PM
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...