HP-67 a nearly hopeless case

[PANAMATIK]

A long time has passed since I aquired an HP-67 in a very bad condition. It didn't show any numbers, and inserting the new ACT, programmed with HP-67E version, didn't change anything. It was a nearly hopeless case, emphasized by a missing battery contact and very dirty battery case. But the keyboard and exterior looked very nice. Therefore it went for a long time into my drawer, but I didn't forget it.

Last week I tried a new approach to make a repair of this sadly dead calculator. Obviously the display driver chip was defective. I replaced it by a repurposed new ACT hardware, programmed with a HP-67 display driver, which needed to run a rather tricky critical timing. Then the display came to life again. But it turned out, that also the CRC chip was defective. But this is not an issue, because the card reader does not work either with the new ACT. But another problem persists: I cannot drive the exponent minus sign! The HP engineers didn't use the anode driver directly for showing the minus signs, but made a special transistor circuit, because they had the problem to use a 14-digit cathode driver to drive a 15-digit display (see schematic). Their solution was to combine two digits, capable of showing only the minus sign, into one. I still don't have a solution, but I will work on it.



The new ACT and new anode driver placed into the processor board, and now the HP-67 is working again.

As a side effect of my repair efforts, I had to draw a HP-67 schematic, consisting of three separate PCAs. I cannot guarantee it being completely error free, but 99%.

HP-67 Processor board


HP-67 Display and keyboard


HP-67 Card Reader


Does anybody know a proper replacement for a missing HP-67 (Classic) battery contact?

Bernhard

[BobVA]

Thanks very much for posting the schematics!

[Geoff Quickfall]

Bernhard:

To say you never cease to amaze is an understatement!

As far as the battery spring contacts go, harvesting from a parts machine is the only option I have seen, if you want to keep the original look.

I have removed the bad prongs in a machine as an experiment. Replaced them with a phone type plug. Milled out a square hole to accept the male end in the battery compartment at one corner. Then purchase a three nicad phone battery pack and plug it in. Close up the battery cover and voila, done.

Charge in the calculator, or use an old house phone to charge the pack externally. Did this for the spice series as they represent the largest failure design for battery prongs.

Geoff

[PANAMATIK]

(05-08-2017 04:51 PM)Geoff Quickfall Wrote:  As far as the battery spring contacts go, harvesting from a parts machine is the only option I have seen, if you want to keep the original look.

Thanks for the confirmation. That is what I expected.

As I don't want to cannibalize my machines, I just found another solution. I used a small sheet of steel from a folder, which showed the right elasticity, and cut it to the right length in a slightly conical shape. It could be fixed very well in the battery compartment from below, because of its thicker lower end. Then I removed the isolation by a dremel tool and now it gives best battery contact.



Bernhard

[Dr. Mabuse]

Hello Bernhard,

Great job regarding to the old HP-67. Have you ever tried a product so called ARMOR ALL for refreshing the calculator plastics colours (e.g. battery pit) ?! I've used this product on my motorcycles plasic items and recently at a HP security cradle with great success. ARMOR ALL and a Q-Tip is your friend !




Regards from the neighborhood,

Thomas alias Dr. Mabuse

[PANAMATIK]

(05-08-2017 07:23 PM)Dr. Mabuse Wrote:  Have you ever tried a product so called AMOR ALL for refreshing the calculator plastics colours (e.g. battery pit) ?!

Never heard of. But they offer dozens of cleaning products. Which one did you chose?

Bernhard

[Geoff Quickfall]

Dr Mabuse:

NEVER use Armorall on the keyboad bezels. It would be okay on the exterior of the shell but NO where near the silkscreened keyboard bezels.

As the calc ages, it is exposed to chemicals (lab environment) and UV. This decomposes the clear lacquer used to protect the silk screened script.

Even a fine make up brush with a dilute solution of dish detergent (liquid) can remove the script. Always pat dry the keyboard bezels, never wipe dry.

Geoff

P.s. Do your have a first name?

[Sylvain Cote]

(05-09-2017 12:39 AM)Geoff Quickfall Wrote:  P.s. Do your have a first name?

(05-08-2017 07:23 PM)Dr. Mabuse Wrote:  Thomas alias Dr. Mabuse

[Geoff Quickfall]

Merci Sylvain


Guess I should have read the whole post :-)

[Dr. Mabuse]

G'morning Bernhard,

I've used the following Armor All product:




Geoff is right - you should use this product for the calculator shell and the battery pit only. A bottle of Armor All is something around 8 Euro bugs.

Best,

Thomas

[brickviking]

(05-09-2017 05:07 AM)Dr. Mabuse Wrote:  G'morning Bernhard,

I've used the following Armor All product:

Slightly off the topic, it was fun trying to translate those ArmorAll labels, I got a pretty good idea though.

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