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HP Forum Archive 20

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41-CX with 'Creeping LCD Disease'
Message #1 Posted by Tim C on 2 Nov 2011, 1:43 a.m.

After 20+ years of flawless service, my 41CX is fading fast on me.

The top portion of the LCD is turning black, like as if someone spilled ink inside.

I see many 41C and 41CV's with Fullnut LCD's available with corroded battery terminals and such for parts but working LCDs and my question is, is there anyway to transplant my in-perfect-health 41CX guts into one of those Fullnut housings and use its LCD?

I've already contacted the HP repair houses and been told the Halfnuts are not repairable, but what about a transplant? Everything on my CX is in fine condition (battery terminals, module sockets, keyboard etc) and my Memory and Advantage modules work 100%, just the display is toast.

I'd hate to lose my trusted partner over this tragic 'Creeping LCD Disease'...

      
Re: 41-CX with 'Creeping LCD Disease'
Message #2 Posted by Paul Dale on 2 Nov 2011, 3:12 a.m.,
in response to message #1 by Tim C

The screen is dead :-(

RIP.

- Pauli

      
Re: 41-CX with 'Creeping LCD Disease'
Message #3 Posted by Raymond Del Tondo on 2 Nov 2011, 4:12 a.m.,
in response to message #1 by Tim C

The cheapest (and least effort) way is to get a replacement 41CX.
Due to the higher chip integration, halfnut displays are not replaceable as easy as the ones in the non-halfnuts.

HTH

Ray

            
Re: 41-CX with 'Creeping LCD Disease'
Message #4 Posted by Alexander Oestert on 2 Nov 2011, 12:51 p.m.,
in response to message #3 by Raymond Del Tondo

Unless the experts say otherwise, you may try to canibalize a C instead of a CX, because it should be cheaper and easier to obtain. I have exchanged keyboards between a C and a CV without problems.

      
Re: 41-CX with 'Creeping LCD Disease'
Message #5 Posted by Cristian Arezzini on 2 Nov 2011, 7:08 a.m.,
in response to message #1 by Tim C

Ouch. But what is that "disease" exactly? Are the two glass plates "separating" too much, or on the contrary, touching? A LCD screen is a relatively simple device, I've never understood why that thing happens. I've had a couple of nice watches and a calculator ruined by it...

Cristian

            
Re: 41-CX with 'Creeping LCD Disease'
Message #6 Posted by sylvandb on 2 Nov 2011, 2:48 p.m.,
in response to message #5 by Cristian Arezzini

Quote:
But what is that "disease" exactly?

Maybe an LCD expert can answer the question with some real details, but from my understanding the seal of the LCD has broken and either air is getting in or the 'liquid' is getting out.

In my experience it is most frequently caused by physical shock, but can also happen if the seal ages and either shrinks or becomes permeable. Sometimes it seems as if the seal might become less flexible and a shock that would have been no problem when new will 'break' an older LCD.

I have a CV with the same problem on the right end of the display after a drop onto that corner. The blackness is just touching the top of the 9th digit and are large part of both the bottom and top of the 10th and exponent digits. The unit also shuts off in about 10 seconds and has other problems as I've been swapping in 'worse' parts. But it still works and sits on my desk as my 'daily driver' scientific calculator. (contesting that position right now with the 15C LE).

            
Re: 41-CX with 'Creeping LCD Disease'
Message #7 Posted by Lyuka on 2 Nov 2011, 2:54 p.m.,
in response to message #5 by Cristian Arezzini

That problem may occur when the LCD had been kept under strong direct sunlight.

The heat from the sun can physically damage LCD unit.
The plastic polarize film absorb the heat ray effectively,
and the LCD unit can be deformed by heat.
The sealing of the liquid crystal can break down to cause leakage.

UV rays in direct sunlight can also cause the chemicals in the LCD to deteriorate.

Lyuka

            
Re: 41-CX with 'Creeping LCD Disease'
Message #8 Posted by Garth Wilson on 2 Nov 2011, 5:37 p.m.,
in response to message #5 by Cristian Arezzini

What I read 25 years ago is that UV will damage it like that (but I don't imagine that would be so localized), and that moisture and heat are enemies but especially the combination of the two. I had a cheap $2 stick-on LCD clock in a car from 1985 to 1992 though since the car's mechanical clock on the dashboard didn't work anymore, and although the car was always parked outdoors (including in the summer), the heat did not seem to affect it at all in those seven years. I seem to remember that on the hottest days it would turn dark, but then come back to normal after I got in and started to drive, cooling it off. There are wide-temperature LCDs that are made to operate at up to 70 degrees C and be stored at up to 85C. (Maybe they go further than that now-- I don't know.) I had a couple here in the office in the 1990's that I was testing for a product that got cancelled, and was testing it at the temperature extremes (including -55C which also did no damage).

      
Re: 41-CX with 'Creeping LCD Disease'
Message #9 Posted by Tim C on 3 Nov 2011, 12:09 a.m.,
in response to message #1 by Tim C

Well if I can't revive this one, is it possible to use the battery terminals from mine in one of the units I see being sold with corroded ones?
I have a hard time buying a "working" 41-CX for well over $350.00
If fact I saw on E-Bay some person selling a CX plus a printer/card reader for Two Grand!! Yikes, I hope no one buys it for that price...

This is sad, those people over-pricing us for old equipment we want/need and HP starving us with unrealistically small releases of the 15-C All the small release of the 15C did was create a market for people on EBay to jack up the price on.

There's no love for us people that actually use these things to make a living...

            
Re: 41-CX with 'Creeping LCD Disease'
Message #10 Posted by Garth Wilson on 3 Nov 2011, 12:41 a.m.,
in response to message #9 by Tim C

Quote:
Well if I can't revive this one, is it possible to use the battery terminals from mine in one of the units I see being sold with corroded ones?
You can get a new flex circuit for the battery and module terminals at http://www.clonix41.org/Maintenance/IO_Block/IO_Block.htm
            
Re: 41-CX with 'Creeping LCD Disease'
Message #11 Posted by Lyuka on 3 Nov 2011, 5:16 a.m.,
in response to message #9 by Tim C

Hi Tim C,

I found a front panel of an HP-41C in my junk box yesterday, and its LCD seems OK.


If you have a chance to stop at Tokyo or Yokohama JAPAN, I can give it to you for free since I have no plan to use it forever (so far ;-).

Lyuka

Edited: 4 Nov 2011, 1:32 p.m.

            
Re: 41-CX with 'Creeping LCD Disease'
Message #12 Posted by Paul Berger (Canada) on 3 Nov 2011, 7:32 a.m.,
in response to message #9 by Tim C

Yes you could use the I/O and battery connector block in another 41 they are all the same. While damage to the battery connectors due to battery leaks seems to be a very common problem, my experience is that there is often other things wrong like broken posts.
To swap the display module in a halfnut you would need to remove the keyboard circuit board which is held in by about 40 heat stakes. The display module in the half nuts also contains ROMs, I looked inside my halfnut CV and compared the part number on the display with a picture of the inside of a halfnut CX on Diego Diaz's website http://www.clonix41.org/Maintenance/hp-41_PCBs.htm and the part number on the display module is different, this may indicate that the ROMs in the CV and CX versions are different. In the halfnut CX not all of the ROMs are in the display module, the CX has a sub board that contains the clock and possibly some of the extra ROMs. It may be possible to swap the glass part of the display if it is connected to the electronics by elastomer connectors like the connection between the electronics and the glass in a full nut, but this can be tricky and just getting to the display in a halfnut is already a big job.

                  
Re: 41-CX with 'Creeping LCD Disease'
Message #13 Posted by Randy on 3 Nov 2011, 1:55 p.m.,
in response to message #12 by Paul Berger (Canada)

Quote:
Yes you could use the I/O and battery connector block in another 41 they are all the same. While damage to the battery connectors due to battery leaks seems to be a very common problem, my experience is that there is often other things wrong like broken posts...

Agreed. The simplest swap-out would be to find another halfnut CX with a damaged i/o block. With a halfnut, you'll avoid the more common post issues that can occur with fullnuts. IMO, circuitry of the halfnut is more robust due to lower parts count.

FWIW, the LCD failure mode is usually a failure of the glass to glass seal resulting in the loss of the liquid.

Edited: 4 Nov 2011, 7:46 a.m.


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