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Service tips for new owners of HP-34C, other spice calc's

Posted by Norm on 5 June 2003, 9:02 p.m.


I have something to say. It's my best information to you, about servicing the HP-34C. Along with other people's suggestions, these ideas should give you enough knowledge to keep it running right.

OF course, we have the great division between these units, of solderless assembly (the chips are merely pressed against the wiring board) and a later subsequent soldered version which seems less common.


SO, the solderless units were a bad idea originally, and you may well have one that becomes unreliable.

For starters, know which version you have. YES, that means opening it up and taking a look-see. NO, I am not going to get into the frightful details of how to separate the lower-edge of the case halves. It is possible but its difficult and that's another story.

What I will earnestly plead... if you have a solderless unit, and it starts getting unreliable on you, STOP using it. I am convinced that a degradation takes place in these units, if the solderless joints are intermittent and you keep on using it. If its healthy, fine, enjoy it (if it aint broke dont fix it) once you see evidence of trouble then take it to the doctor.


As to how to bring a solderless unit back to fullest performance (if the connections go intermittent) I have some answers there, though maybe not all.

I tried repairing one by soldering it with a controlled temperature precision iron. I think it wasn't the best idea, so you can learn from my experiences:

Firstly, the pins themselves may have built up a blue oxide, esp. on the 3 small memory chips. This oxide not only may contribute to the bad connections, butit also prevents you from soldering the pin down. The pins don't want to accept solder.

So they weren't tinning. The only way to fix that was flip the chip on its backside, and rub it for awhile with the iron.

Secondly, even with the lowest controlled temperature, there was a tendency to melt the plastic underneath the connection.

Thirdly, you can never undo this type of work, so if a chip blows you can't replace it and the supply of parts rapidly dwindles.

I would favor the Luiz Vieira approach....... pull it apart and clean up the contact surfaces with a cleaner. Then use some type of light-oil that would keep the surfaces more corrosion resistant (dont know what oil, probably a switch-lube oil.

The chips themselves, well, flip them upside down, and look for cleanliness of each pin. Probably a bit of scraping with a jewelers screwdriver is all that's needed. I think Luiz was using a bit of emery paper, which might be OK if followed by a squirt of aerosol degreaser to make the abrasives go away.

A low-power stereozoom microscope is just dynamite for this. You can see exactly what's going on with each pin. I have one...... although they are $800 new, it can be such a fine tool that I say its totally worth the money. It's a Leica Zoom 2000, stereo, 7 - 30 power with built-in illuminators.

THE LAST THING is ESD. I dont think you stand a snowballs chance in Hell of being able to clean up all the pins on an ancient CMOS chip without frying it. The only way this will work is if you ground yourself out, like by stuffing aluminum foil into your socks, ground the jewelers screwdriver out, have everything grounded using alligator clips, and work on a piece of anti-static plastic or perhaps a piece of aluminum foil while you work each pin of a chip on its backside. Even that might be a bad recipe, often ESD is best handled with weakly conductive paths, not strong ones. Pick your strategy and run with it. I'd probably go with hard-metal connections for a job like this, especially to myself, and work atop aluminum foil.

Anyway, clean all these boundaries where the contacts occurs, a bit of oil on everything, put it back together and cross your fingers.

That's the Luiz approach, and its better than what I tried.


Do recommend lubrication of the switches, or they will grind flakey bits of metal where the contacts are sliding. And these are antiques that there's no turning back (unless this whole country gets more traditional in its thinking, from the boardroom on down). So we really need to cherish these items.

I think we can take a line from the antique radio crowd...... "you are dealing with a nostalgic item that goes beyond just your personal ownership. Later it will be owned by another person. Do any work so that it will last and ould please the future owners also".


Still recommend "Tri Flow" for slide switches (the teflon version of WD-40, from the black aerosol can), shake well, but only one drop of the liquid onto a Q-tip and then rub it onto the slide switches while everything is apart.


HEY one OTHER VERY IMPORTANT IDEA about SPICE calculators (dont think people have bought into this yet, but Luiz is starting to). Starting with the extraordinarily difficult case-halves, and continuing with the inner plastic clips that retain the electronics module, this plastic was mis-designed and you have to bend it TOO MUCH to get the molded plastic ratchets to spring away.

In these situations, get out a fresh X-Acto blade, and trim away just .010 or .020 of that plastic. Do it manually. THEN, the ratchet action comes apart easier, for future service. Don't get carried away or you wreck it. But a little plastic removed can make for easier disassembly w/o damaging it.

If we don't get into doing some of that, the clips will simply break off in future servicings. I know because I'm already seeing bust-offs of these clips inside.

Try it sometime and you will be well-pleased.


These tips will hopefully keep your unit running happily even if it is a solderless unit.

As to battery power.... personally I recommend feeding it with AA Alkaline cells, and just dispose of them when they run down. At 38 cents a battery, from a competitive source, it's a small price to keep such a nice unit running. Others may wish to keep employing the charger. Still another option is Photo Lithium disposable batteries. However, the "Energizer" version of that has no more mA*Hr than the AA Alkaline (either is 2900 mA*Hr). Maybe another brand has truly high capacity.


When it comes to HP-34C, enjoy the most cosmetically charming little portable that HP ever made, and take good care of it, after all, eventually I plan to own all of them.



- Norm


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