HP Forum Archive 06

[ Return to Index | Top of Index ]

HP-97 f key Message #1 Posted by Pierre on 30 Oct 2001, 10:10 a.m. Hi! A friend recently give me a nice HP-97. Unfortunately, the x2 and the f keys don't work. For the latter, it is very annoying. I took the machine apart: the keyboard contacts are ok, no dirt, no corrosion (as they are in gold). I cleaned them nevertheless, but the problem remain. Any idea ? Pierre

Re: HP-97 f key Message #2 Posted by Tony Duell (UK) on 30 Oct 2001, 7:12 p.m., in response to message #1 by Pierre I assume that the x2 key is the 'x squared' key, right? Electrically, the HP97 keyboard is a rectangular matrix of keys. 4 columns and however many rows are needed (14?). The 2 keys you mention -- f and x^2 -- are not in the same row, and they're not in the same column. Assuming all the other keys work correctly, there can't be a problem with the keyboard interface circuitry. ROM failure is, I suppose, possible (the machine could lose the routines needed to handle these keys, but _very_ unlikely. No, the only likely cause is bad contacts on the 2 keyswitches, or broken connections (PCB traces, vias) to them. That's what I'd check first.

Re: HP-97 f key Message #3 Posted by Pierre on 1 Nov 2001, 5:46 a.m., in response to message #2 by Tony Duell (UK) Thank you Tony for your help. All circuitry and contacts are OK. May be for the f key there is an electronical problem ? I don't know how the calculator work internally, but I suppose that the strike on the f key have to be kept somewhere in memory until a second key is pressed ; so may be there is a problem with this memory ? It is a bit difficult to test this calculator when taken apart, particularly the keyboard, as when the printer and the card reader are not connected, it doesn't work. All the best Pierre

Re: HP-97 f key Message #4 Posted by Tony Duell (UK) on 1 Nov 2001, 6:32 p.m., in response to message #3 by Pierre It's possible there's a logic fault, but I think it's fairly unlikely. I still suspect the keyboard itself. As I mentioned, the keyboard is a 4*14 matrix. The 4 columns go to the ACT chip via the first 4 pins on the 18 pin connector on the keyboard PCB (the pins are numbered from the end furthest from the 9 pin connector, that is to say they are numbered from the printer side of the machine). The 14 rows are scanned by the display cathode driver chip -- the 20 pin chip on the keyboard PCB, possibly marked 1820-1629. Remove the keyboard from the machine (or at least remove the printer, logic PCB, and support plate). Now connect a continuity tester between pin 1 on the 18 pin connector and pin 4 of the cathode driver chip. You should get continuity when the 'f' key is pressed. Then try connecting the tester between pin 4 of the 18 pin connector and pin 12 of the cathode driver chip. This time you should get continuity when x^2 is pressed. If the keyswitches are OK, then it would appear to be a ROM problem on the logic board. As you have a parts unit (I think), you might try swapping out the 18 pin chip (1818-0225) ROM0 on the logic board, and then the 5 little 8 pin chips on the same board with the ones in your other machine. Those are the ROMs.

Re: HP-97 f key Message #5 Posted by Pierre on 11 Nov 2001, 9:15 a.m., in response to message #4 by Tony Duell (UK) Tony, You were right. There was a bad contact under the two keys. I had to slightly bend the contacts to make them work. It was a bit difficult to find the good balance between full contact and no contact at all, but I finally succeed. Many thanks for your wise advices, Pierre

Re: HP-97 f key Message #6 Posted by Tony Duell (UK) on 11 Nov 2001, 4:57 p.m., in response to message #5 by Pierre Happy to help, and I'm pleased that another fine old HP calculator is working again :-)

[ Return to Index | Top of Index ]

Go back to the main exhibit hall