41CL installation on machine with zebra strip


My preferred donor calculator, a 41C with a dead CPU, meets the specifications for the 41CL except that its CPU board connects with the white zebra strip connectors instead of the desired wired-wrapped-around-a-tube connector.

That said, the existing connectors seem to be in fine shape and there seems no obvious physical reason they wouldn't work. Has anyone installed a 41CL circuit board in such a machine? Would long-term reliability be better with the other connector?


I have one CL board installed in a 41C with such elastomeric strip. It works fine, so far no issues. I also heard of others who installed it in similar setups, no bad reports. So it may be that although less preferable it´s also a valid configuration, I don´t know the reasons Monte had to recommend not to use those.


I have two 41cl using elastomeric strip to about 2 weeks and not showing any error
I also like to know the reason for not using

My uninformed guess is that Monte is concerned about the resistance of the zebra strip posing a problem during high-current operations, particularly during flash writing which could corrupt the firmware.

I saw this problem with a card reader and a dodgy zebra connector. Everything worked fine until it tried to read a card then the 41 would malfunction. Replacing the connector with a PW connector fixed it.



Yes, this is the reason that I don't recommend using this type of connector. Everything will be working fine until the (relatively) high current is needed for the Flash write operation. This is exactly where a contact failure will be a problem, as it can lead to corruption of the Flash memory. Unfortunately such memory corruption is not necessarily restricted to the sector being written, so the OS might be affected, which is very bad news.


OK, good to know. Moving on to the 41CV with the correct display and serial number...and the correct contact thingy.

Too bad one of the lower posts came off with the original CPU. Sigh. And there are no hobby shops in Reno and Home Depot does not carry styrene cement. Perhaps I can order some online.


Can you put the zebra connector in the CV, then use the printed wiring connector to install the NEWT board in the C?



Tried that, but all I get is random scrambled flashes on the display...which is also what I get when I put in the known good CV board, so I conclude that my dead 41 has problems in the keyboard or display circuitry...


Bummer - well at least you know you're not losing out on a good host due to lack of a PWC.

You might want to put up a separate post with the symptoms and see if someone (Randy!) has an idea for troubleshooting/repair.



The "dead 41" is a machine I acquired years ago, for parts. I don't really care if it never works again; the only question now is if there any are usable parts in it at all. If a good CPU doesn't work in it, and its CPU doesn't work in other machines, I might as well toss it...

In the meantime I found some styrene cement at a local crafts store and am waiting the requisite 24 hours for the repaired post to set.

Edited: 29 Dec 2011, 7:36 p.m.


Hopefully it was the liquid solvent welder, not thick cement... also, just as important are the screws. Early C's and CV's had 0.25 inch long screws in the lower posts. The short screws are the cause of most post failures. HP changed these out to 0.375 inch length screws in all later and serviced units.

Shoot me an email to my museum address if you need a set of screws and new rubber feet. I was going to contact Monty to see if he wanted to add these to the CL kit but he doesn't have an email :(


I would love a set (or two) of those screws, thanks! I just ordered extra rubber feet on eBay so I can pass on those.

The cement I used was a thick gel similar to what we used to call "airplane glue." However I used very little of it. I guess the stuff I should use is a rather thin liquid, right? Guess I'll have to find that online.

I see Geoff's paper wherein he not only glues the post but puts plastic shavings down the hole and a drop of solvent on top of that. I can try that as soon as I get the correct glue and some screws.

In other news, I installed the 41CL board in a 41C I had. It wasn't my first choice due to a slightly mushy "1" key (but it still works perfectly). The CPU board was actually held in by two silver nuts threaded over the plastic posts. I initially thought this was something someone had done to the machine, but the inside of the back case was different, too: on the other machines I've looked at, the plastic posts on the keyboard half fit into recesses on the back, and the back is designed to apply pressure to the CPU board when it's on. This back wouldn't work that way; it's obvious the nuts provide all the pressure.

Not only is this more reliable, it means cracked posts should be less of a problem.

In any case it all went together easily and now I have a working 41CL, finally! Now all I have to do is repair the 41CV I screwed up.


Amazing the number of thing they tried rather than screws, isn't it? :-)

Geoff just put up an interesting post on the hex nut approach.

Glad you got it working!


Edited: 30 Dec 2011, 4:49 p.m.


In other news, I installed the 41CL board in a 41C I had. It wasn't my first choice due to a slightly mushy "1" key (but it still works perfectly).

This is a common problem in "tall key" 41C's. Most have less travel in the 1 and many times the 2 key giving the impression of "softness".

I've never pulled a board off one to figure it out why it only happens in those early units but I suspect they changed the frame and stake configuration to resolve the problem. The nuts used to attach the logic board amplify the problem so keep them as loose as possible to minimize the effect.

Installing longer screws will make the whole issue of the wrong glue a moot point. I would not remove them again just to re-glue. The plastic shavings trick, again, totally unnecessary with the correct screws.

BTW, "correct" is my way of saying tri-lobular plastic threading #2 sized screws, not plain old sheet metal spiral threaded types.


monted (at) systemyde.com

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