Cases for 38E/C



#12

At some point I'm probably going to want to replace the case of my 38C - three of the six latch posts that hold the innards to the top case are broken. My 38C is one of the later versions where the ICs are soldered in. Did the case change when HP went to this new design, or could I use any 38C case (or even any 38E case) as a replacement?


#13

Hi;

please, have a first look at this article and its pictures:

As you can see, there are two different cases because there are two different assemblies. One of them you already know, ant the other one is a solderless version: the IC´s, LED assembly and power supply unit are connected to each other through a flex circuit. As explained in the article above, their contacts are pressed with the flex circuit contacts through a metal plate locked by two clips in both left and right sides. This type of assembly is thicker than the one you have hence the posts being a bit taller. Their internals do not fit in each other cases.

I repaired an HP38E with two broken posts. First I used an acrylic solvent (must see the chemical composition) to set it in place. After fixed (one day drying out) I placed some acrylic in the outer part of the post, and that fixed it in place (one extra day for drying out). I'll add pics later, OK?

Success!

Luiz (Brazil)

Edited: 30 Oct 2009, 6:52 p.m. after one or more responses were posted


#14

Thanks very much, Luiz. Well that means I would have to find another soldered-version 38C to replace the case. Can I use the serial number to make that distinction?

I can't use your glue method bacause I don't have the broken pieces. They must have been broken long ago, and weren't there when I opened the case.

If the serial number won't tell me which model it is, is there a measurement I can make that would tell me without having to open the case? Thickness perhaps? When my calculator is resting on the desk, it is 1.25 inches (31.5 mm) tall at the highest point. Are the unsoldered versions thicker than that?

Peabody


#15

Hi;

externally they have no visible (nor measurable, AFAIK) difference. I cannot be sure if the serial numbers would be of any help, because refurbished calculators may have a new interior with the same, previous serial #. The best approaches I can offer you without opening the calculator are:

1 - weight - the solderless version without batteries weight (almost) the same as the soldered version WITH batteries; this is due to the metal plate the solderless version have;

2 - key course - the solderless version use flex circuit for the keyboard, and their keys almost level the keyboard faceplate when pressed (they go deeper inside); the soldered version needs almost half the angle to close their contacts.

Apart of that, the only way is to open the calculator. I have a spare Spice upper case with a very faded keyboard faceplate, but I am not sure if it is from a soldered or a solderless unit, and I also have to find it. I'd gladly send it to you, but you'd have to replace the keyboard faceplate. If I find it I´ll let you know.

Success!

Luiz (Brazil)


Edited: 30 Oct 2009, 6:21 p.m.


#16

Thanks, but don't go to that trouble at this point. I may have found a dead one locally, and should know about that by next week.

#17

Hi;

I disassembled a solderless HP31E I have because it needs some work in the upper case (a small crack). So I decided to measure the difference between the posts in the upper case of a soldered HP38E that is already opened with the ones in the HP31E. I could not find any difference between them, the posts seem to have the same 'tallness'.

Interesting! I vividly recall building a soldered unit in a solderless case and noticing it was loose. Now I have no reason to keep that memory... What the h@#*!

Well, I apologize not checking it twice as I did now.

Cheers.

Luiz (Brazil)

Edited: 30 Oct 2009, 8:24 p.m.


#18

Hi Luiz! I sadly discovered today that several of the Spice's that I restored years ago no longer work. Batteries were fine (replaced with lithium cells). It was the %$#& ribbon cables. I guess that they continue to deteriorate if they have any corrosion on them. I fixed a 34C tonight, I have one 32E to go.

I hadn't though of restoration being an ongoing project!


#19

Hi, Doc.;

could I say 'Good news, afterall!? Well, your HP34C is back to life, and this is always good news, right?

I have observed that the HP41 has the same problem, i.e., once the batteries contacts show corrosion, cleaning and/or replacing only the contact tips will not always stop corrosion to go inside the flex circuits. I have two unusable contacts+I/O assembly. If we consider the thickness of the copper tracks and the amount of chemicals that have already been in contact with them plus the atmosphere elements (mainly oxygen), it seems to me an additional neutralizing component is needed after cleaning the leakage so it does not go ahead 'eating' the cooper. I achieved some acceptable results with sodium bicarbonate solution (I hope this is the English term for that). It is normally used to wash recently corroded PCB to neutralize the ferric perchlorate (I also hope this is the correct term...) so the final PCB is not slowly corroded by the remaining perchlorate. BTY, did you use a computer flat cable to restore the HP34C? I have an HP38E waiting for a transplant that will happen today, if time is not against me, and I'll use it. Luckily I'll replace only the three-track part of the ribbon, not the whole flex circuit.

Hope you succeed bringing the HP32E back to life. It is a fine statistics-addressed Spice.

Cheers.

Luiz (Brazil)

Edited: 2 Nov 2009, 12:51 a.m.


#20

"bicarbonate solution (I hope this is the English term for that)"

"sodium bicarbonate"

Here in America we call it baking soda. Is readily available in any grocery store and is useful for absorbing odors and neutralizing acids on car batteries, in swimming pools and many more uses including enhancing shampoo so as not to use as much.

Charlie - Phoenix USA

#21

Thank you Luiz and Charles! I have repaired these by cutting the ribbon cable and super-gluing the remaining cable down and baring the copper with a grinding wheel. Then just two wires soldered to the remaining cable and then directly to the back of the battery terminals. (I haven't tried to retain rechargeability).

Can sodium bicarbonate solution be applied with a brush to the cable so the whole machine doesn't have to be disassembled when not needed?

The problem I see there is that the cable is "sandwiched" in plastic and the corrosion seems to find its way between the plastic layers....


#22

Hi, doc;

Quote:
(...) the corrosion seems to find its way between the plastic layers...
This is the main problem, as I see. I do not apply the sodium bicarbonate solution directly, I use it (in a 10% volumetric relation with the water, maybe less) to dip the corroded parts in it for a while, then I press them from time to time to allow the solution to reach the deepest possible. After that I wash the parts in current water, dry them out then I apply a thin coat of some micro oil, like WD40 or any other, with a small brush. This is to reduce contact with the atmosphere and to protect a little bit in case of leakage. The micro oil does not cause bad contact when the surfaces are well cleaned and pressed accordingly.

The HP41 demands some extra care because of the rubber foam used to press the battery+I/O assembly contacts. It should not be dipped in the sodium bicarbonate solution.

Success!

Luiz (Brazil)

Edited: 2 Nov 2009, 2:26 p.m.


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