HP-97 sudden death

[wine+dine]

Hello everyone,

I have an HP-97 on which I fixed the card reader and printer and rebuilt the battery pack. For some time all worked fine, then one day after a charge cycle the machine did not respond anymore. Battery voltage is fine. I also checked the inverter, Vss and Vgg are OK (6.25 / -12.2 V). The calculator draws ~350 mA (~140 without the printer board) but there is no display and no visible digital activity (no Phi 1/2 clock, strobe or other signals). Reset to the ACT chip is OK.
Does anyone have any other ideas or do I have to assume the ACT is dead?
Thanks in advance!
--WD

[PANAMATIK]

My 97 draws 170mA when 0.00 is displayed with printer board connected. No Phi1/2 is the problem that you have. Did you measure 720 kHz at Pin13/14?. The oscillator LC components are located on the printer board. Check 330pF, 150uH and the printer board connection. ACTs normally don't pass away without reason.

I'm working on ACTs for HP-97, but they are not yet ready.

Bernhard

[Katie Wasserman]

I haven't played with this for a while, but from what I recall you can't just pull the printer board out, you need to jumper a couple of connections to get the calculator to work. I need to look at the schematic to confirm this and will report back the jumpers needed.

[wine+dine]

Thank you Katie and Bernhard. It is understood that the LC tank needs to be connected - I disconnected the printer board only to locate the excessive power draw, which turned out to be the printer motor being driven. With the LC connected, I do get 733 kHz oscillation on pins 13/14 but alas, no other digital activity anywhere. Phi 1/2 float high to 4-6 V and slowly fall down below 0.5 V when loaded with 2k2.
Doesn't look so good I guess ...
--Peter

[PANAMATIK]

(12-27-2014 01:21 PM)wine+dine Wrote:  With the LC connected, I do get 733 kHz oscillation on pins 13/14 but alas, no other digital activity anywhere. Phi 1/2 float high to 4-6 V and slowly fall down below 0.5 V when loaded with 2k2.
Doesn't look so good I guess ...
--Peter

Doesn't look good for your ACT.

But there is hope even for the HP-97. I desoldered the ACT of my fully working HP-97 for experiments with the new ACT and its already partially working. Its a challenge, but I'm confident I can help you in a few month. If I had more time, it could be faster.

Bernhard

[wine+dine]

Very interesting ... what kind of replacement are you working on? Controller or FPGA based?

--Peter

[PANAMATIK]

(12-27-2014 08:30 PM)wine+dine Wrote:  Very interesting ... what kind of replacement are you working on? Controller or FPGA based?

--Peter

See my thread http://www.hpmuseum.org/forum/thread-2445.html

I wasn't able to find a FPGA solution, which I liked to prefer first for getting the accurate timing, but they have hundreds of IO pins and there was no space for it, also some other reasons didn't fit. it's controller based.

Bernhard