41CV Gone Wild!


See the original post of the same title at 17 May. This is a follow up.

The solvent recommended is methylene chloride, aka methylene dichloride (MDC), aka dichloromethane (DCM). I've found out that it is used in paint strippers, as a blowing agent in polyurethane foams, and as a decaffeinating agent, and that it causes cancer (depending upon whom you listen to). Nevertheless, I can't find any to use on my calculator. I found some paint strippers that contain it, along with a host of other unpronounceables, but not the straight stuff. As expected, any time I ask a store employee for help finding dichloromethane, they look just as lost as I do. Where can I find this stuff? Is there a brand name I can ask for?

Thank you in advance.


Look for plastic welding solvent cement sold in hobby stores. It is a clear, water-like liquid found in small bottles with a brush in the cap. It is the only thing that will penetrate the small cracks in the posts.

The right stuff usually says it causes cancer. But then, what doesn't?

Might not be available in all countries.


The stuff I use is called TENAX (X7R?). I get it at Hobbytown for about $3 for a small bottle. At one time there was a person on Ebay selling 2 liter bottles of reagent grade for around $10.


I found the Tenax at Hobby Town. Seems to have done the trick! Thanks to all who have had input. Hopefully I will be able to pass this or other information along to others in the future.


I found it as "Ambroid ProWeld" at a hobby shop -- clear, in a small glass bottle with a brush for ~$3.00 .

I'm not sure whether this is PURE methylene chloride -- I think it "contains" that key ingredient.

Incidentally, I (re)discovered a way to tighten up stripped screw posts in my still-not-working (#*&%$*&@!) HP-41CV: I shaved a sliver of plastic from inside one of the port covers, inserted it into the post hole, brushed around liberally with ProWeld, and then used a toothpick to hold the sliver against the interior post wall while the solvent did its thing. Where the screws used to simply turn ineffectually, they now bite nicely.


Hi, Paul;

as you may have noticed, I don't like bad news and stuck (HP) calculators. What's wrong with your HP41CV?

Can we help anyway?


Luiz C. Vieira - Brazil


It's a fullnut.

The behavior (it does behave at least!) is consistent, but consistently bad. The leftmost columns of keys seem to have been randomly reassigned. They seem to consistently invoke the wrong operations.

For example, the 8, 9, EEX and back-arrow keys work correctly. But the 1 acts instead like the 9, and the 2 acts instead like the EEX. The shift key turns on the SHIFT annunciator, but the next keypress will consistently result in the wrong operation. Some of the unshifted keypresses will invoke operations which should be shifted(!?!?) (For example, the LOG key shows and executes the "ATAN" function.) Some keys cause non-alphanumeric symbols to be inserted into the display.

I can go into ALPHA mode, and start pressing the keys in sequence. I don't remember what comes out (I could reconstruct that easily enough), but in general, it's as if the keys generally on the left side and middle of the keyboard are "offset" in their alpha values by 4 or five places in the alphabet, while the rightmost keys give the proper letter. Very weird!

I've chased keyboard traces and tried to see whether the "1", for example, looks electrically like the "9" has been pushed, but to no avail. Within the capabilities of my limited diagnostic resources, the keyboard and display seem to be functioning fine.

Anyway, there's no way (that I know of) that such a cross-connection in the keyboard could explain the mapping of unshifted keys to shifted functions. I suspect a zapped ROM, with a scrambled jump- or lookup-table has caused a random reassignment of key functions.

I've messed WAY too much with the lower screws, posts, and zebra connector. I've tried soldering the CPU board to the keyboard, first with wire-wrap wire, then with ribbon cable. I've brushed and cleaned, and scraped around solder pads and . . .

None of that seemed to change anything. It's consistently behaved the same, so I'm suspecting ROM damage. If anyone has any other suggestions, I'd LOVE to hear 'em!


Hi, Paul;

I have what left from three HP41's I could rebuilt two. This remaining carcass has two damaged ROM chips and one that is probably good.

If you look at the DIP 8-pin chip codes in your fullnut's mainboard you'll see three of them are 1LE90X and the others (RAM) are 1LA701 (all of the full-nut have it) and a set of five 1LB70x. If data is consistent, I can send this suspiciously good ROM of mine (worthless) so you can test in your HP41CV.

The one I have is the mid one, if I am not wrong it's an 1LE907 (not in fornt of me right now). E-mail me your actual address and I'll send it for you. If you test it and it does not change situation, keep it with you anyway and do whatever you want.

If it works fine, consider it a gift. As I mentioned before, I have no use for it. I was waiting for an actual chance to use it in a fair "mission".

Best regards and let's hope it's a solution.

Luiz C. Vieira - Brazil



You wrote:

If you look at the DIP 8-pin chip codes in your fullnut's mainboard you'll see three of them are 1LE90X and the others (RAM) are 1LA701 (all of the full-nut have it) and a set of five 1LB70x

Your description sounds as if there are a total of ten or more 8-pin chips on the fullnut main board. I only see seven on mine: five attached directly to the board, and two more, each stacked on top of one of the other five.

With the capacitor to the upper left, and the 8-pin chips across the top, reading from right to left, their numbers are:

ILG901 (attached directly),
ILA701 (stacked on another -- can’t read its i.d. code),
ILH502 (attached directly),
ILH503 (attached directly), and
ILH505 (stacked on another -- can’t read its i.d. code).

Also on the board are:
  a large 30-pin DIP across the middle 
(the CPU? – I can’t see the numbers because of the buzzer disk);
a 14-pin DIP running along the “left” side, below the capacitors
(“1826-0953-1” / “RAYL8336”); and
there are pads for a 20-pin DIP on the right side, but no chip there.

Thie 8-pin chip set doesn’t sound very much like what you described. Perhaps you can advise me as to what I’m dealing with (and whether your ROM is likely to help)?


Paul B.


Hi Paul, folks;

as I like making public all of the informaion I can get here or anywhere, I'll reproduce the e-mail I sent you so anyone else that needs the information will ahve access to it, O.K.?

It seems to me yours is a newer HP41, maybe the newest of them all. As you post, I understand that yours has only one ROM chip, and I guess it's the 1LG901. The 1LA701 is a RAM chip and it has the sixteen system registers (stack, ALPHA, flags, controll, etc.) and the remaining 1LH50x are the remaining RAM, being the 1LH501 the first 64 registers (you do not see it) and the 1LH505 the last 64 ones. The other one you do not see is the 1LH504.

In my description, the set 1LE906/7/8 compose calculator's ROM, and they sem to be replaced by the new 1LG901, available in your model. In this case, the 1LE907 I was about to send you would be of no help at all. You need the complete set - 1LE906/7/8 - or another 1LG901.

Thank you for your valuable information. I was not aware of this new "chipset". As I collect information, this is something to be saved.

Thak you again and success! If you need anything else, be my guest.

Luiz C. Vieira - Brazil


I stopped couting and 41C/CV CPU board variations at around 8. I suspect there are over a dozen.


about finding your mdc; do you have a tap plastics near your home?

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