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HP Forum Archive 19

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HP97 restore project
Message #1 Posted by Alberto Fenini on 4 Jan 2010, 10:21 a.m.

Dear All, Happy New Year !

I know has been said over and over and over so forgive me, but, can I put a working ACT from an HP25 into a non working HP-97 ? The HP-97 is the version produced after the HP-97S was available.

as always, thanks for help, Alberto

      
Re: HP97 restore project
Message #2 Posted by Vieira, Luiz C. (Brazil) on 4 Jan 2010, 12:34 p.m.,
in response to message #1 by Alberto Fenini

Ciao, Alberto;

As far as I know, the only ACT that is not compatible with the others is the one found in the HP27. The HP27 uses V-MOS ICīs, and its components cannot be used in other C-MOS circuitry.

Can you compare the printed code over the ACT you want to use and the one you want to replace? I have changed ACT chips from HP25 and HP21 units with no problems. I also red about an HP67 using an ACT from a HP25 donor.

Cheers.

Luiz (Brazil)

Edited: 5 Jan 2010, 5:14 a.m. after one or more responses were posted

            
Re: HP97 restore project
Message #3 Posted by Alberto Fenini on 4 Jan 2010, 4:43 p.m.,
in response to message #2 by Vieira, Luiz C. (Brazil)

ciao Luis, the working ACT from HP25 is : 1820-1523, while the one I think has to be replaced is 1820-1596, what do you think ? Take care Alberto

                  
Re: HP97 restore project
Message #4 Posted by Michael Meyer on 4 Jan 2010, 7:35 p.m.,
in response to message #3 by Alberto Fenini

I think it should work. I've transplanted several to 67's, and I think the 97 has the same ACT, but I'm not certain. You may have to be the one to let the rest of us know for sure....

                        
Re: HP97 restore project
Message #5 Posted by Randy on 4 Jan 2010, 8:36 p.m.,
in response to message #4 by Michael Meyer

Yes, the 67, 97 and 29C use the same ACT. The ACT from a 25 *should* work.

The 21 ACT will not work as it lacks the I/O expansion signals.

                              
Re: HP97 restore project
Message #6 Posted by Alberto Fenini on 5 Jan 2010, 4:12 a.m.,
in response to message #5 by Randy

Very good, I'll try later today or tomorrow and keep you posted, has anybody tried desoldering with hot air ? Cheers, Alberto

                                    
Re: HP97 restore project
Message #7 Posted by Randy on 5 Jan 2010, 8:22 a.m.,
in response to message #6 by Alberto Fenini

Quote:
Very good, I'll try later today or tomorrow and keep you posted, has anybody tried desoldering with hot air ? Cheers, Alberto

That will not work for through hole devices, way too much heat required, you'll destroy the board in the process. Solder wick or a vacuum desoldering station is the only way.

                              
Re: HP97 restore project
Message #8 Posted by Eric Smith on 5 Jan 2010, 12:46 p.m.,
in response to message #5 by Randy

Quote:
The 21 ACT will not work as it lacks the I/O expansion signals.

That might be true of part number 1820-1396, though I've never tried it. All other ACTs that might be found in an HP-21 should work in most ACT-based calculators other than the 27.

There are some compatibility issues between certain ACT part numbers and old firmware in the 67/97, and possibly a few other models. The 1820-1596 ACT is known to have these issues.

                                    
Re: HP97 restore project
Message #9 Posted by Randy on 5 Jan 2010, 1:21 p.m.,
in response to message #8 by Eric Smith

Quote:
...That might be true of part number 1820-1396, though I've never tried it.

I have, that's why I posted it. Your post also explains why there are other ACT's in early 67's and 97's. Thank you for the info!

BTW, are there DNS issues with brouhaha? Can't seem to load anything.

                                    
Re: HP97 restore project (mother board)
Message #10 Posted by Alberto Fenini on 6 Jan 2010, 5:47 p.m.,
in response to message #8 by Eric Smith

And here we go, that's what I did today ...


old ACT

ACT from HP25 soldered on HP97

how far I went .....

Since the result wasn't what exactly I had expected, I have re-soldered the original ACT chip, and surprise surprise, I'm now in the situation where a flickering and random bunch of zeroes will light up for a second when the switch goes from off to on ...too fast to take a picture...
I can also hear the printer making noise if this is of any importance.
However, since on both units (I'm using a working HP97 to test progresses)the printer gear needs to be replaced,I have to keep the printer switch in manual mode.

I have then decided to divide the project in two sections : motherboard repair and display with keyboard repair

At this point, I'd like to hear some suggestions from all of you. What can I do with the described behavior ? On the motherboard I have re-soldered most of the chips, and I could do it radically, if anyone would suggest that a bad contact could be the reason of this behavior.

As for the display/keyboard unit, when used with the working motherboard, it reamins completely off .... Would you suggest replacing the chips ? I have noticed that the transistor arrays (1858-0044)are exactly the same used on the printer card, so I could easily have a source for them. I know these to work since I have swapped the printer unit back and forth in the past.

Or would you suggest that the 1820-1629 could be responsible for the display remaining black ??

Any, and I mean any, suggestion will be of great help, and I'll be glad to try it out.
Take care, Alberto

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