28S Advice Needed

[twoweims]

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.

[C.Ret]

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][ > ] ?

[twoweims]

(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.

[C.Ret]

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.

[Steve Simpkin]

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

[twoweims]

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...