New (to me) 41CX and a question

[Xorand]

I recently purchased a 41CX on eBay that just came in today. It was advertised as unknown working condition but looked great, including the battery terminals. It came with a dead rechargeable pack, but I put a normal pack in it with 4 new N cells and it works. So now I have a CV (fullnut) and CX (halfnut).



On both the 41CV and today on the 41CX, sometimes after putting the battery pack in the calculator it won't turn on. Usually it will start working if I push the battery pack up against the springs as if getting ready to remove the pack but leave the pack in. It might takes 3 or 4 attempts before it starts up.

Question: Is this potentially just the need to clean contacts? Note that both calculators have very nice and shiny battery contacts - no green or dark discoloration or deterioration at all. Also, the CX is very tight. I have had to rebuild the bottom posts on the CV before (last summer, I think I posted that on here).

[Monte Dalrymple]

The springs in the bottom of the battery pack also get corroded, and it's harder to see than corrosion on the battery connector block.

[Xorand]

(05-18-2022 09:39 PM)Monte Dalrymple Wrote:  The springs in the bottom of the battery pack also get corroded, and it's harder to see than corrosion on the battery connector block.

That was a thought I had prior to posting. I might take both packs and give the springs a good cleaning.

[rprosperi]

Often, there is oxidation/junk which you can't see, even looking up close.

The simplest/best tool for this is a glass brush like this:

https://www.amazon.com/gp/product/B0019V18D2

It's basically just a bunch of strands of fiberglass in a small pencil style holder which you use to rub the exposed faces of the contacts on both sides.

On the contacts in the 41 itself, don't press too hard as you can easily scrape it too much, just a gentle brushing is fine and nearly always enough.

In the battery holder, just rub the tops of the spring contacts.

I would have never believed this simple solution would work, but trying it made me a believer.

[DrewNicholson]

Aloha,

Nice calcs!

You might want to get a bottle of deoxit, progold and get a copy of the very excellent hp-41 repair book:

https://smile.amazon.com/gp/product/B000...UTF8&psc=1
https://smile.amazon.com/gp/product/B001...UTF8&psc=1
https://www.amazon.com/gp/product/B08JJD...0df70867f0

I got the kindle version and I think I shall order the printed one as well.

Since you have already done a post repair I'll assume you already know how to get in there and don't really need the book, and you might not need the deoxit or progold, and they are nice to have.

I also will get myself one of those fiberglas pens! Thanks Bob!

Here's the catch with battery terminals. They can look clean, but the problem is actually underneath where the flex board wraps to the expansion ports.

I decided to check the function on my 3 NOS 41C's last night, and I discovered they are not NOS, I just had bought very nice almost complete boxes. That makes more sense anyway. I was motivated to check because a CX with some paperwork went out for $375 on ebay yesterday. Yow! I'm sure it's a very nice calc and I see the barest hint of green on the battery terminals. It's an '88 halfnut, and it looks like there may be battery terminals in the power adapter port. I used to know this stuff offhand, and I don't recall that there were any 88's with battery terminals. It's possible this has been repaired. But the battery terminals go with the back, and the serial number is on the back, so it seems more likely I'm wrong about this. Then again, it may be possible to add the terminals, which is just more confusing!

https://www.ebay.com/itm/165478326094?nm...7675.l2557

On my boxed 41C there was some green cancer and I used deoxit on the terminals and I could get some life in the display, so I know I will be able to get it working again. Hopefully I got the deoxit in there enough to resist further corrosion. I'm guessing I bought it knowing there had been a repair as there is some copper foil on the two center conductors on the battery connector which would have been in any pictures. Part of the reason I bought it was because it was sold at the Iowa State Bookstore while I was a student there and I got it from the original owner.

This motivated me to dig out my old '2034 C (1980 tall keys) as it has bad corrosion and I thought I better get it arrested. I used deoxit on the battery terminals and it had a little life in the display. Since it was mostly missing the feet, I decided to dive on in as I would not be messing up said feet. What I found inside was surprising. Not only was there corrosion on the zebra connector wrapping around, there was corrosion on the circuit board traces. All cleaned up easily with deoxit. The most interesting thing was the solder drop on the zebra connector where it pressed to the circuit board. Clearly this had also been repaired. I don't recall the owner telling me it had been repaired, but this was 25 years ago. I bought it because of the tall keys and it came with a card reader, which I did not have one at that time.

Let's see if a link from OneDrive works ...

https://1drv.ms/u/s!AkfXbjQEO0N2hNVcUmly...A?e=n04oNu

I got a lot of corrosion off of it:

https://1drv.ms/u/s!AkfXbjQEO0N2hNVLW2Oa...w?e=kiChql

The takeaways here are:

1) If you are serious about buying a nice 41 and are willing to pay the price (see ebay above), you can't assume the current owner knows the full history of a calculator that may be 40 years old. Educate yourself, look super closely at pictures, and ask for more if you need them.

I don't know if I would be willing to pay $375 for a CX when I can buy a DM41 for so much less. 25 years ago it was cool to try to have one of absolutely everything, but it seems a bit insane now. If I had returned and caught up on things a year ago I would have turned a C into a CL. I have a lot of manuals and stuff that are probably of value only to serious collectors at this point as there is no reason to buy them.

As a serious collector, it's going to be worthwhile to educate yourself which will save you money and tears!

2) If you have the green cancer, it gets to the underside of the foil and it will eventually eat away everything. Deoxit is likely the best defense against this ongoing corrosion. The tall keys C pictured above is working, and I'm going to get a new part from the calculator shop when I go to fully repair this guy.

I am quite confident that if there is *any* cancer and put the calc in a box for 20 years, it's gonna have a lot of green on it if you didn't use deoxit :-)

A nice addition to the family!

Mahalo

[cdmackay]

I have a 41CL with a similar issue; built by José so am assuming it's all OK internally, I don't want to risk opening it myself.

Springs have been replaced; I wonder whether it's either small differences in N-cell length (I'm using Duracell), or spring compression/stiffness?

[Xorand]

I appreciate all the fine advice. I do have DeOxit spray and liquids. Maybe I'll give that a go on the springs. I'll also look into that fiberglass brush.

I saw that CX go for $375. I had it on watchlist purely out of curiosity. I got my working halfnut CX the other day on eBay for $200 (offered) including shipping. It was advertised as "not sure if it works" and came with a rechargeable pack. I put a replacement regular N cell pack in it and it worked right away (aside from the aforementioned retries) and is in great shape.

It also had Thermal and Advantage Pack modules in it. I figured if it didn't work, I could probably sell the modules, case, etc. and make up a good deal of the $200. I'm also not afraid of tearing into it to see if I could figure out any issues between having rebuilt the posts in my CV fullnut and all the information here on the forum.

Edited to add: Amazon is bringing me a fiberglass scratch brush tomorrow. It's nice living right down the street from a major Amazon warehouse.

[DrewNicholson]

(05-19-2022 11:59 PM)Xorand Wrote:  Edited to add: Amazon is bringing me a fiberglass scratch brush tomorrow. It's nice living right down the street from a major Amazon warehouse.

It really is - there’s one about 8 miles away and they built another about 4 miles (I’m a bit north of Denver). Amazon just keeps rolling up the score against any competition.