HP 97 keyboard and more issue.

[Ignazio Cara (Italy)]

Hi guys, I need your help with a faulty Topcat HP-97, serial number 2008B65177 and mother board 97S like. When turned on, show 0.00 at the display, but it don't receive input by the keyboard in RUN mode, display light-off if any key was depressed in PRGM mode. If something is sent to the printer, show 'Error' and if a card is inserted in the reader appear incongruous data on the display and the driving motor not start.
I have tried to make some substitution among the electronic component taken from a working PCB. Step by step I have replaced the PIK 1820-1952 with a 1820-1723 ( is it compatible?), the ACT, the ROM 0, ROM 3 and ROM 6. Nothing to do, the calculator show always the same issue. I have tested the voltages Vss and Vgg. With a Vbat = 5,20 I have read the following values: Vss= + 6.00 and Vgg = - 11.61. Unfortunately I do not have an oscilloscope to check the SYNC, STR, RCD, Ô1 and Ô2. What other measures can I do with a multimeter to see what does not work? Thank in advance for your kindly help.

Edited: 18 Jan 2010, 9:55 a.m.

[Ignazio Cara (Italy)]

Sorry, but I have forgot to say that the display-keyboard assembly, printer and card-reader works flawlessly if installed with another main PCB.

[Randy]

Has the behavior changed in any way with the parts that have been exchanged?

Same question, different way: Are the current symptoms identical to the original symptoms?

[Ignazio Cara (Italy)]

Hi Randy,
I'm very glad to hear from you, thanks.
No, nothing is changed before yesterday. I have changed the zener CR10 and now the Vss and Vgg are 6.27 and -12,01 Volts respectively. I don't remember how many times I have checked the PCB, my next action will be change the CRC as well. After this attempt, the dark night. You have any idea about this?
Many thanks for your efforts.

Ignazio

[Randy]

PIK and CRC should have been the last IC's to swap, ALL the roms would have been my first choice.

All roms and the ACT are by far the most common failure parts.

[Ignazio Cara (Italy)]

My next action will be to change ROM 1, 2 and 5 (550, 551 and 229), becouse the ROM 0, 3 and 6 have been already changed. as so as the ACT. I'll keep you informed, for now thank you very much.

Ignazio

[Ignazio Cara (Italy)]

Hi Randy,
I have replaced the ROM5 (1818-0229) and....success, all the issues disappear. But now I must find a good ROM5, I have one with bad RAM section. Have you a 0229 for sale? Let me know please and many thanks for your kindly help.
Regards from Italy

Ignazio