HP41CV "No-Nut"


I have found another "NO-Nut". This time it is a 41CV. There is no PCB board. It is built into the key/display board. Are these units rare? I have seen the insides of many 41's, but only two like this. I have a 41C and a 41CV like this. Photo's of the 41C can be seen here: http://photos.yahoo.com/bc/ty__77705/lst?.dir=/My+Photo+Album&.src=ph&.order=&.view=t&.done=http%3a//photos.yahoo.com/bc/ty__77705/lst%3f.dir=/My%2bPhoto%2bAlbum%26.src=ph%26.view=t



AFAIK the last C/CV's which were produced have this PCB layout. I had a fullnut CX when it was new (must have been around 1983-84), then swapped for the 'nonut' version of the CX half a year later because of the better display.

Regardless of the amount of 'nuts': Those were (and still are) very cool calcs!





I have both CV and CX halfnut as this one in the photos, but I was not known about C's like this. I thought the memory was built inside the central PQPF (or is it in the display assy?), so there was no way other than using another IC to reduce/change maximum memory size. Have you tried a MEMORY LOST, SIZE 000 and PRGM sequence? What do you see in the display: 00 REG ??? (319 or 63)? I have one 41CV (cocnut/fullnut) with the contacts' keyboard detatched from the upper half box. It is not difficult (just time consumming) to remove it AND replace it, if you want. As we can see in the third photo, it IS a 41C's box (Silver stripe around the keypad instead of the CV/CX's golden stripe)

Maybe you are familiar with the the 41's operation and you have already done the memory test. If so, excuse-me asking to do that. It's just for checking if it is not a CV built into a C box.



MEMORY LOST, SIZE 000 and PRGM sequence results in 00 REG 127 on the 41C. On the 41CV it is 00 REG 319.



Original HP41C should result 00 REG 63. If you read 00 REG 127, it is like an HP41C with one 82106A Memory Module attached to it. Strange... I have never seen something like it. Does anybody know the reason? Is there such an HP41C?



OOPS, I did have the memory module in. It does read 00 REG 63. Sorry For the mix up.


If you don't like it give it to me.



I think there may be a jumper or two that can be used to trim down the falfnut CV memory to 41C size. Somebody told me HP was going to use this so they could use halfnuts for service replacement machines but usually just sent out CV machines instead.

BTW, I have a 41CV machine with silver trim and silver front label. It is an early fullnut with the CPU card held down with the nuts.


Just wondering...

Let's suppose Ty Rogers want to free the existing 256 blocked registers; would it be easy to find the jumpers and remove them? Say, I understood that no-nut (halfnut?) 41C's have the registers AND they may be blocked (unaccessible). Is it correct?

Just wondering...


If you can find them it should be possible to reverse their positions (I don't know if they were cut or installed to disable the memory). On some other HP machines the jumpers usually looked like two triangles with their tips touching. These could be cut apart at the join. Others looked like two semicircles with their diameters parallel. You could short them together with a solder blob. The person I heard about them from was told by an HP service tech during a casual conversation. I don't know if all machines have them or only some of the earlier ones.


The information I have suggests that all memory (ROM and RAM) in the halfnut C and CV is on the display hybrid circuit (the CX has another hybrid mounted across the top of the CPU containing the extended memory, timer, and extended functions ROM).
Moreover, the CV display hybrid contians a ROM chip, RAM chip and display driver. The C hybrid contains just the ROM and display driver. I don't know where the RAM is on a C -- maybe in the CPU or the display driver itself.
I've never seen any links on a CV display driver hybrid to disable the RAM chip, though. They might exist. You'd have to take the top case apart (undo the heat staking on the keyboard) and desolder the display assembly
to investigate, though.


Hi, Tony;

Your info is (as always) consistent, but I was taken by surprise. So, the HP41C had a halfnut version alright... Amazing!

That's complete new info for me.



Yes, halfnut 41Cs exist (I don't have one, though). AFAIK (and the info I have confirms this), they
were never sold as such (the 41C was discontinued before the halfnuts were made). They were used as replacements for 41Cs sent back for repair if HP couldn't
(economically) repair them. That's why they're very hard to find...


and rare piece, mostly cause it was not even sold.

Good info. I'll keep my eyes oppened...


Yep, I've heard of those halfnuts going for ludicrous prices here in Australia.

I've never seen one for myself.

Griggsby Malone

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