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Hello,

I just bought an old non-working HP67 in a garage sale yesterday, and i'd REALLY like to revive it. I kinda got attached to it even after one day :)

It seems like the battery leaked into the PCBs, most of them (mainly the one with the main controller) were corroded. I cleaned what I could very carefully, and changed the battery (with standard 3 AA batteries).

The screen now displays a line of _ (underscores) characters, except one digit (which might be broken). The keys have no action, neither has the prgm/run switch.

Does someone know what makes it display _, and what that indicates? Which part might be working/broken, so I can narrow down my search to the defective part. Is there hope? What do you think? Could you give me general advices on repairing this beautiful little toy?

Note: I wasn't so careful in the cleaning of the card reader part (the motor is even unplugged). Can it be the cause of the _?

Thanks in advance,


--Matthias

Wow, sorry for this very quick update...

After letting it on just the time of writing my last message, the display just changed (i was just pushing buttons randomly): It now displays:
-00000000000
That's it.
Is the controller dead? or can it still be caused by a bad connection? Or a broken discrete component? The enigma is still full.

PS: Seeing it display actual numbers just gave me even more motivation to repair it. Please help me!

--Matthias

Quote:
Is the controller dead?

That is very difficult to say without an oscilloscope.

Quote:
can it still be caused by a bad connection?

Very likely if there is significant corrosion.

Quote:
a broken discrete component?

Unlikely, unless someone worked on it before you.

The best method to troubleshoot would be to install a known good processor board to verify the display and keyboard PCB are good or place the suspect processor into unit with a known good keyboard/display PCB. Bad LED's and display drivers can cause all manner of strange behavior so it is easiest to divide the problem causes in half.

If the corrosion has actually gotten onto the processor board (pretty rare), look for damaged traces and corrosion on the connector pins.

Any chance of some photos so we can see the extent of the damage?

Edited: 3 June 2007, 8:42 p.m.

Sure, here are some photos:

http://www.flickr.com/photos/mqtthiqs/tags/hp67/

Quote:
The best method to troubleshoot would be to install a known good processor board to verify the display and keyboard PCB are good or place the suspect processor into unit with a known good keyboard/display PCB.

Of course but I don't have another one to test this. In case someone around here lives in Paris, FR and have one...

Quote:
If the corrosion has actually gotten onto the processor board (pretty rare), look for damaged traces and corrosion on the connector pins.

I can't see any when I look though the proc PCB with a strong light, but the broken track could be hidden under an IC. I have to buy a multimeter to test them thoroughly (anyway I don't know how I lived these first 25 years of my life without one).

Another idea is to unsolder all components, clean the PCB and re-solder them. Do you think it would make sense? What should I do first?

Thanks for your advices!

PS: Is there any good reverse-engineering material about this calculator out there? With the exact pinouts of every component, I could test them more efficiently...

Hello!

Quote:
Another idea is to unsolder all components, clean the PCB and re-solder them.

Don't do that! Unless you have access to professional unsoldering equipment (you can get several working hp-67s for what that costs!) you will only fry your integrated circuits to death and damage the PCB.
From the photos, the PCB dosen't look too badly corroded anyway. But the keyboard is probably beyond repair, so fixing the circuits will not restore this calculator to working condition anyway :-(

Look out for a better '67 and keep this one for spares, just in case.

Greetings, Max

There is an article about the HP-67 in the article-section of this website:
http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=394

It would appear there is a fair amount of corrosion under the keys on the bottom half of the display circuit board. I would check for shorts between the columns and rows of the keyboard. Any leakage from the corrosion can cause display problems. Pinouts can be found at 67 Internals

A good method to remove the corrosion is to stand the board on end in vinegar for about a half hour. Rinse several times and dry in a warm place.

Thanks to you all for the advises.
Maximilian: Thanks, but i'll try to repair it anyway. I can't help it.

Randy:

Quote:
A good method to remove the corrosion is to stand the board on end in vinegar for about a half hour.

Wow, I didn't know that one! Do you submerge it totally? What type of vinegar do you usually use? The red one or the white one? Do you dissolve it?

White is best, full strength right from the bottle. Put it in a jar so that you can stand the board on end in the vinegar. You only want to submerge the key strips and contacts, not the IC's or LED's at the top of the board.

Hello,

I'm beginning to give up. This is where my electronics skills stops.

I did what Randy told me, I went actually even further: I cleaned the whole keyboard and logic PCBs with vinegar (it worked amazingly well), and I checked every connections I could with a multimeter. Everything seems to work fine, and power seems to arrive into the logic PCB. But then I can't see any current arriving in the ICs. I think the voltage converter on the logic PCB is dead (and I really don't know how to fix it): as soon as I put the battery in, one of the transistors in the upper-left corner overheats very fast.

If someone has another idea, something I should try or change before giving up totally, please tell me.

I'm VERY disappointed, but now I have to overcome this and think about getting a normal life back. This little toy was so cute! Maybe one day when I have courage, I'll try to replace the PCB with some microcontroller and write a HP67 emulator for it.

Thanks to all of you for your wise advises!