HP 29 & 21

[zixingcheche]

hi

is it possible to change the PCB of HP21 into HP29?

I have a not working HP29, I want to put my working HP21 PCB in to HP29 chasse.

thanks!

[rprosperi]

No, you cannot swap the PCB, the 21 and 29C have many different components (ROM, RAM, etc.).

However you can use the ACT from a 21 to replace a failed ACT in a 29C. This was long thought impossible, however PANAMATIK was able to successfully repair my 29C with an ACT from a 21 and it behaves fully correct, including Constant Memory, Programs, etc.

[teenix]

Also, the inter board pin connections are a bit different and the keyboard won't give the ACT the correct key values.

cheers

Tony

[zixingcheche]

(11-12-2022 03:24 PM)teenix Wrote:  Also, the inter board pin connections are a bit different and the keyboard won't give the ACT the correct key values.

cheers

Tony

thank you, I got it.

[zixingcheche]

(11-12-2022 01:06 PM)rprosperi Wrote:  No, you cannot swap the PCB, the 21 and 29C have many different components (ROM, RAM, etc.).

However you can use the ACT from a 21 to replace a failed ACT in a 29C. This was long thought impossible, however PANAMATIK was able to successfully repair my 29C with an ACT from a 21 and it behaves fully correct, including Constant Memory, Programs, etc.

thank you, got it!

[zixingcheche]

please check the pic.
my 29C shows "0" when power on.
if I change the ACT chip from HP21 to this HP29C. does it works? thanks!

[rprosperi]

It will work if the ACT is the only bad component and there is not other damage. The 29C also has RAM chips (21 has no separate RAM chips), which could also be bad, and it's possible other components on the board have been damaged.

Did an old battery leak acid residue into the 29C? Do you see any evidence of blue/green residue on the board or on any components? If you can see ANY residue then the entire board must be cleaned to remove, which can be difficult as the green gunk often seeps under chips may have done damage, even if the surface of the PCB and components look clean. Check carefully and remove any residue that you can see with Q-tips soaked in vinegar.

Just to be sure you know, NEVER plug HP's power adapter into any 29C, doing this is what kills the ACT and possibly other components. Either use Alkaline cells, or charge NiCD or NiMH cells in an external smart charger.

[zixingcheche]

(11-13-2022 04:32 AM)rprosperi Wrote:  It will work if the ACT is the only bad component and there is not other damage. The 29C also has RAM chips (21 has no separate RAM chips), which could also be bad, and it's possible other components on the board have been damaged.

Did an old battery leak acid residue into the 29C? Do you see any evidence of blue/green residue on the board or on any components? If you can see ANY residue then the entire board must be cleaned to remove, which can be difficult as the green gunk often seeps under chips may have done damage, even if the surface of the PCB and components look clean. Check carefully and remove any residue that you can see with Q-tips soaked in vinegar.

Just to be sure you know, NEVER plug HP's power adapter into any 29C, doing this is what kills the ACT and possibly other components. Either use Alkaline cells, or charge NiCD or NiMH cells in an external smart charger.

Thank you so much for your kindly comments & advices. I’ll try to clean the pcb first, and then try to exchange the ACT chip.
Thanks!

[teenix]

(11-13-2022 02:14 AM)zixingcheche Wrote:  please check the pic.
my 29C shows "0" when power on.
if I change the ACT chip from HP21 to this HP29C. does it works? thanks!

The HP-21 ACT is 1820-1396, the HP-29C is 1820-1596 (also with HP-25).
The HP-22 ACT is 1820-1523, with pinouts same as 25, 29C.
HP-27 is NMOS so ACT from it is likely incompatible.

External connection differences are the PWO input and the DATA line (both missing on HP-21)

Bob has mentioned swapping them will work, so these two functions look to be implemented inside the ACT's, with the data bus and reset logic not used for the HP-21.

If the ACT's are all compatible (with exception HP-27) then serial number differences might be just chip design modifications.

cheers

Tony

[AndiGer]

Eric’s website is back online and always a perfect chip reference.
http://www.brouhaha.com/~eric/hpcalc/chips/
Andi

[zixingcheche]

Hi teenix, AndiGer

Thank you for your informatiom.
I checked as below:

My 29C: 1820-1596 ACT AMI, Mostek MK6216N
My 21: 1820-1396 ACT AMI

I will try to exchange these ACT, thanks!

[zixingcheche]

I still have one concern that the sn of 29c is start from 19(1979)
And the sn of 21 is start from 15(1975)

Dose it matter? Old ACT chip works in new PCB?

[teenix]

(11-13-2022 09:01 AM)zixingcheche Wrote:  I still have one concern that the sn of 29c is start from 19(1979)
And the sn of 21 is start from 15(1975)

Dose it matter? Old ACT chip works in new PCB?

I think just try and see, I doubt it will hurt anything. Be careful handling the IC's, they can be damaged by static electricity. Double check the chip orientation before powering up. Take a photo of the original chip in position before removing.

As always, do not power these calculators from the AC charger - batteries only.

cheers

Tony

[rprosperi]

As I mentioned probably too casually, it was long thought these different ACT chips may not be fully compatible (the item Teenix points out and I think there may also be others as well - I don't speak chip), but years ago, when Bernhard confirmed my worst fears that my 29C ACT was bad, we figured (just exactly as Teenix states) that there is no harm to try it, and it will confirm once and for all if indeed all the (same process) ACT chips were created the same, as a 21 ACT (being the first) would be about as different as possible as a 29C ACT (being the very last model 4-5 years later) if they were not the same, and to our surprise, it works perfectly.

Of course, it's still not ideal to rip the heart (ACT) out of a working 21 simply to repair a 29C, but at that time I had a 21 with (IIRC) bad display components, so it was an ideal donor.

hth

[brouhaha]

(11-13-2022 01:41 PM)rprosperi Wrote:  years ago, when Bernhard confirmed my worst fears that my 29C ACT was bad, we figured (just exactly as Teenix states) that there is no harm to try it, and it will confirm once and for all if indeed all the (same process) ACT chips were created the same, as a 21 ACT (being the first) would be about as different as possible as a 29C ACT (being the very last model 4-5 years later) if they were not the same, and to our surprise, it works perfectly.

The NMOS ACT from the 27 isn't electrically compatible with any of the others. I believe there are some subtle functional differences between some versions of the PMOS ACT, because HP had to revise the microcode in the 67/97 ROM0/anode driver for a later ACT version. The newer ROM0 will work with either the older or newer ACT. That's documented in the later edition of the 97 service manual.

The 19C/29C ROM microcode is very closely related to the 67/97, so it's possible that the same subtle ACT difference might apply to them. IiRC, the 19C and 29C each have two ROM0 versions, like the 67 & 97, possibly for the same reason. I haven't yet tried to analyze the nature of the difference. Maybe someday.

That's independent of the 67/97 ROM1 and ROM2 change, which have to be swapped together as a pair. That change was to fix the trig and lastx bugs, but would work with either tho older or newer ACT and ROM0/Anode.

If I had a Woodstock with bad ACT or RAM chips, I'd buy the Panamatik ACT replacement. And in fact a friend gave me a dead 25C recently, so I should do that.

[zixingcheche]

Hi all

I exchanged the ACT. now, HP29C is with the one from HP21's.
the symptom is still keeping "0", and the keybroad doesn't work. but the on off switch works.
It seems there are other parts are not working well in side HP29C.

any advise? thanks!

[teenix]

(11-14-2022 06:27 AM)zixingcheche Wrote:  Hi all

I exchanged the ACT. now, HP29C is with the one from HP21's.
the symptom is still keeping "0", and the keybroad doesn't work. but the on off switch works.
It seems there are other parts are not working well in side HP29C.

any advise? thanks!

It appears you may have a faulty ROM and/or RAM IC.

I tried running my 29C emulator and alternately failing each ROM and RAM but I could not recreate the faulty display you have. This doesn't really much as one or more of the 65,536 ROM locations, if faulty, could output any value between $000 and $3FF.

The only real way to test is with an oscilloscope to track the Is and DATA buses.

cheers

Tony

[teenix]

Sorry, other things to check are the power supply rails for correct voltage and perhaps the reset components, the ACT has a small 2u2 capacitor and there is a reset chip as well.

Some of the capacitors in the power supply may be failing.

Also, check for corrosion on the circuit board which may have caused broken traces.

cheers

Tony

[zixingcheche]

teenix, thanks!

I just changed back the ACT to the HP21, everything is OK in HP21.
so, the ACT from HP29c is good..

I will check the defactive 29c as your comments later

thank you very much!