HP67 - can be programmed but then does not work

[ovalsa]

Hello all,
I have an interesting problem - I have purchased a bit corroded HP67. Opened it, cleaned, put together again. Switched on in RUN mode it displays 0.00 but the calculator does not make any calculations. When you hit any key the display shortly blinks (normal behaviour) but it shows zero all the time. When switched to W/PRGM mode it is possible to enter a program and calculator responds fully correctly to all keys (the codes are generated and written to the memory correctly). The program cannot be executed (switched to RUN mode it does nothing except of short blink of the display).
Does anybody have any idea where to try to find the problem ??
Regards
Ondrej

[teenix]

It would seem that the keyboard, display, pgm/run switch all work ok, so it could be a faulty ROM.

If there was corrosion, check the connections on the ROM ICs, maybe there is a bad connection on one of them.

There is a lot of key/display processing in the ROM space between 0x0C00 and 0x0FFF both in run mode and program mode so probably ROM3. Unfortunately I don't have hard documentation that says what memory space each ROM IC occupies, but probably the one marked as 1818-0231.

cheers

Tony

[Marcovecchio]

Tony, while on this subject: what are the options once we conclude one of the hp67 ROMs is faulty?

Is there any solution on replacing all 4 ROMs, for example, with a microcontroller that would emulate the ROM chips?

Or the only current choices are to replace with a good ROM from another hp67? Or, of course, substitute all internals with your replacement board, or use Panamatik's solutions?

Thanks!

[teenix]

(04-17-2022 12:24 AM)Marcovecchio Wrote:  Tony, while on this subject: what are the options once we conclude one of the hp67 ROMs is faulty?

Is there any solution on replacing all 4 ROMs, for example, with a microcontroller that would emulate the ROM chips?

Or the only current choices are to replace with a good ROM from another hp67? Or, of course, substitute all internals with your replacement board, or use Panamatik's solutions?

Thanks!

This could all be done, it just takes time. The main problem is getting IC's these days, they are becoming hard to find with the global IC shortage continuing. Most delivery dates just for what I need are "sometime" next year. Even if they become available, bigger companies have probably snapped them up.

cheers

Tony

[ovalsa]

Hello,
I made some further research - the problem is clearly in the ROM/processor board (I have the second fully working HP67 and this board shows the same problem in both of them when the other board works everywhere). Is there any possibility to analyse / fix the problem ?? I am still struggling with throwing this nice piece of history into trash bin (but what else can I do with the calculator which does not make any calculations ??).
Any recommendation will be appreciated.
Ondrej

[teenix]

(04-20-2022 08:20 PM)ovalsa Wrote:  Hello,
I made some further research - the problem is clearly in the ROM/processor board (I have the second fully working HP67 and this board shows the same problem in both of them when the other board works everywhere). Is there any possibility to analyse / fix the problem ?? I am still struggling with throwing this nice piece of history into trash bin (but what else can I do with the calculator which does not make any calculations ??).
Any recommendation will be appreciated.
Ondrej

You will need an oscilloscope to help diagnose the problem.

I can help you out, but there will be an overseas postal bill.

Also, if you decide to throw it out, please send it my way :-)

cheers

Tony

[Marcovecchio]

If Tony gives up, I would like to have it too!

I have two non working hp67, and having some more parts to swap would help me diagnose and hopefully, have at least one working machine!

Eduardo

[vaklaff]

(04-20-2022 08:20 PM)ovalsa Wrote:  I am still struggling with throwing this nice piece of history into trash bin

I wish you best of luck. However in case of that horrible trash bin finale let me know in time so I can come in person with my trash bin :-) I'd use the calculator to house the replacement board teenix makes.

[Dreato]

I have a working HP67 MB I can send you. PM me with address etc. International shipping is SLOW.

Regards,
Dave