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Display problem on 34C



#2

I recently became the happy owner of a 34C. It seems to work perfectly apart from a few observations of dimming and flashing of parts of the display.

I can't figure out if it is just the standard non-soldered Spice contact problem. To the me it seems a bit strange: After using the calculator with no problems for some time (at least some minutes), part of some digits, the sign or the whole of one or more digits dims for a few seconds, then the display flashes like if you press a button and the machine goes on working like before. The whole scenario happens while the machine is just left on the table (not touched at all). No data is lost. I can’t provoke the problem mechanically by squeezing or twisting the house.

I don't know at all if my unit is the non-soldered version. The serial number starts with 2040S (as I understand this should mean produced in Singapore in year 1980 week 40. Is that right?). Could anybody tell from that which Spice generation (non-soldered or soldered) my unit belongs to?

Any advice before I dress up for the surgery is highly appreciated. Thanks.

/Steen


#3

Hi, Steen;

there are two "EXTERNAL" differences between the soldered and solderless Spice (all HP3x-series) types: the weight and the keys "movement amplitude" (I cannot remember a word for this... Sorry!). Unfortunately you'd better having two units so you could compare.

Solderless models are heavier because they have a metal plate inside to keep structural "linearity" and integrity. Now that I'm mentioning this fact, it woobe a good idea to simply measure both weights... ;) If there is a non-destructive way to check for metal parts (metal detectors?), maybe this would also be useful. As a brief comparison, if measuring with your own hands, solderless units without batteries are about the same weight as soldered IC's units WITH batteries installed (I have two units in hands right now). Anyway, still not a good information...

Keys in solderless units need a wider "angle" to reach the contacts. This is because their contacts are provided by "plastic bubbles" under each key; they use a flex circuit and the (amazing) solution was using a single plastic assy with the contact surfaces and circuit trails for the IC's and both contacts for keys. The "bad news" is that the cooper in the bubbles seems to suffer a "movement stress" and tend to "crack" in old, too-used units. I saw a few calculators with this sort of trouble, but it happens. I think a brief "description" of these angles will help you better:

- choose one of the keys in the first row (e.g.: prefix keys) and look at one of its side while you press it;

- observe the face that's closer to the display when the key reaches the end-of-course;

- if the mentioned face has more than half of it hidden in the keys' hole, it's a solderless unit;

- if just a small part of it (less than a half) is hidden, i.e., it moves a little bit only, it's a soldered unit.

Units with soldered IC's have metal caps for key contacts, the same kind used in the HP41 series. That's why they need a different "angle".

Hope this helps identifying your unit. And if it is a solderless unit, chances are you have a bad contact somewhere in the many contact surfaces. To open it... well, that's another story. If you have no clues about where to go after removing the two screws under the batteries "door" and you realize there's something still keeping both upper and lower halves togehter, hold on for a while.

Let us know if you need guidance to "accomplish the mission".

And congrats! Among the LED-display models, I consider the HP34C along with the HP67/97 and the HP55 as the best ones. Yes, I know that are others like the HP65, all Topcats... But many of them are great collectible items and, except for the HP55, these are some of the easiest to find.

Luiz (Brazil)


Edited: 26 Dec 2003, 1:36 a.m.

#4

Hi Steen:

It should be a problem of bad contact, probably the on/off switch with old and dirty grease.

Best Regards

Jon


#5

Dear Luiz and Jon

Thanks a lot for your input. Following Luiz's instructions for inspecting the key angle, it seems clear that my unit is from the solderless generation.

I'll try to see what a drop of contact/relay rinse spray can do to the on/off switch before I warm up the soldering iron.

I'll keep you informed on the progress.

Thanks.

/Steen


#6

Hi, Steen;

I'm glad "you made it!"

Anyway, if you are willing to go ahead and you are sure yours is a solderless unit, consider that a soldering iron will be no good solution. Unless, otherwise, you're using a technician "jargon" ;), for what I'm sorry not getting it :(

As you mention a contact rinse spray, take into account that the contact "button" is designed so the fewer contamination material reaches the contact surfaces. Maybe even for achieving the "rinse" cleaning you'll have to open the unit. If you do so, take the chance to clean the IC's contacts, too. Using this sort of cleaner is something I strongly recommend instead of "mechanical" cleaning, like surface scrapping.

Also, there is a little "trick" when reassembling the unit. There are three small 8-pin DIP IC's (two ROM, one RAM) that have the same orientation and are "assembled" in three different positions. The one closer to the display is always the RAM IC because this specific position is the only one that is powered by the batteries when the calculator is OFF and the batteries are installed and charged (continuous memory). The other two positions share the same contacts for each IC pin.

I remember I saw some solderless Spices with some symptoms like the ones you mention, with the difference that the missing digits used to get "back to life" when the calculator was slightly "twisted" so the contact surfaces would rub each other a little bit.

Success!

Luiz (Brazil)

Edited: 26 Dec 2003, 8:39 a.m.


#7

Spraying contact cleaner into the switches will not help, only hurt. It will disovle the grease inside and carry into places it should not be, the keyboard.

Luiz is 100% correct, keep soldering irons away from your 34C, it will only do damage. Also, again 100% correct about mechanical solutions - DO NOT scrape any of the connections - you'll remove plating and that gets ugly.

IMO you need two things for Spice maintenance - a small tube of plastic safe white grease with Teflon (available at hobby stores) and a small can of Caig Deoxit D5 (available online and electronic tool supply houses).

Disassembly is described here by David Smith: http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv013.cgi?read=38078 That long thread has some good stuff in it.

Apply Deoxit to the battery contacts and charger port (they almost always have copper salts growing on them) and rub away the blue/green stuff with a cotton swab.

I think Steen has it right about the on/off switch - most likely culprit from your description. Once open, clean up the old grease from the two switches with some isopropyl and re-lube with the new grease. It only needs a film for protection. Hopefully the plating will be intact and not down to the copper.

Note the position and part number of the chips before popping the two springs off either side of the keyboard assembly 'cause they're gonna fall out. In a little plastic lid, lay down a puddle of Deoxit and soak the flattened part of the chip leads in the liquid. Apply a film of Deoxit to the board side of the chip connections, let soak for a minute or two and rub gently with a cotton swab. Repeat.

Reassemble and enjoy.

Edited: 26 Dec 2003, 9:04 a.m.

#8

Hi Luiz and Randy,

Thanks again for sharing your knowledge. And thanks for bringing me out of a total misunderstanding: From browsing though some old archive stuff on the Forum, I got the impression that trying to solder the chips (one of the postings used the term "convert the solderless unit to a soldered unit") was the only reliable solution to the Spice contact problem. As a matter of fact that procedure sounded a bit scaring to me, so I was very happy to get your advice. After studying the material pointed out by Randy, I do feel much more comfortable. Following Norm's remarks on ESD, I'll wait with the cleaning procedure till I get access to a proper ESD protected lab after New Year. Sorry gentlemen for wasting your time by not studying the available material before asking, but you surely saved me from a lot of tears and most probably my 34C from a terrible disaster.

/Steen


#9

Steen,

While there have been cases of solderless units that have had chips soldered into place, it's a really risky way to fix one as you are soldering onto a thin film plastic substrate. Too much heat and it's good-bye 34C.

I've had better luck with the antioxidant treatments which is far less risky.

I never bought into the theory that ESD could cause the 2 bug - what are the chances of units hit with ESD all failing in the same way? Pretty unlikely. I would be inclined to believe a change in microcode somewhere caused it. I say that because I've never had a failure in an HP that I would attribute to poor handling and or ESD. While I wouldn't recommend waltzing around on synthetic carpets while working on calculators I don't think you need to go full-blown air/wrist/foot treatment for protection. Good insurance if you have access but don't let it stop you.

While there are lots of great nuggets buried in the archives, it's darn hard to find specific information since you can't search very well. Until then, we rely on one another to remember old threads and point us to the tidbit we need.

Edited: 26 Dec 2003, 5:00 p.m.


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