41C Frustration



#2

I have a recently acquired 41c with a bad contact somewhere.
I have pulled it apart multi times and cleaned all the connectors.

The calculator will turn on and work basically ok but.
The lower left of all characters are not solid black.
The calc will turn itself off after 6sec.

I can get around the 6sec turn off by setting "ON" but it still is REALLY anoying.

I would suspect the soldering on the display but on the odd occasions when the display works ok the calc stays on for more than 6sec as well. Tells me its not the display connectors.

Can someone give me any hints?

Thanks Malcolm


#3

You probably have a bad solder joint on one of the jumpers that go between the motherboard and the LCD display driver board. These are small pieces of metal that look kind of like connector pins, and are soldered at each end. Try gently lifting each one with a fine object such as a dental pick. These solder joints are prone to failure and can lead to this problem.

Also clean all contacts (especially the zebra connector to the CPU board) with an isopropyl alcohol pen and make sure everything is snug. Don't overtighten the screws, as the posts are prone to breakage.

Good luck !

- Ed


#4

Hmmm.

Lots of cleaning done multiple times = EXACTLY the same

If its the solder joints on the display -
Why when it goes in this mode does it turn off after 6sec?

This is very repeatable -

good display ( by twisting case slightly ) - no turn off

bad display - turn off in 6sec.

Thanks Malcolm


#5

Hello, Malcolm;

May I ask a few questions?

1 - what type of HP41 you have: full- or halfnut? (if it has a mainboard and zebra connectors, it is a fullnut)
2 - (silly question; forgive-me) have you opened and cleand internal connections or just batteries and external module's connectors?
3 - have you checked to see if screw posts are O.K.? No one broken or cracked?

About the solder connections: the LCD module in the HP41 controls its operating state when the calculator is switched to ON. When you execute the ON function (as you mention as being an anoying procedure, and I agree with you, its anoying) the LCD's command to switch the calculator OFF is bypassed. So, the bad segments (light-gray instead of dark-gray) and the 6sec operation are the very signs that you have a bad connection in the LCD module.

I'm sorry this is not so much help, but may clear up a little bit.

Success.

Luiz C. Vieira - Brazil


#6

To Luiz,

Its a 41c.

I have taken it to bits and cleaned multi times.

All the posts are ok.

The connector type is almost like a millipede looking from top. Very fine gold connectors in half circles.

Two nuts holds the board down firmly over the connector.

Are you saying the lcd module itself decides when to shut down the machine? Thats wierd. But if that's true then that would perfectly explain it. I was thinking the lcd module can't shut down the machine - therefore problem is not in display connector. - Wrong.

If thats the case what precautions should I take when resoldering these wires? I'm worried about the cmos. My soldering expertise is a bit a... agricultural. Any sugestions?


Thanks Malcolm


#7

Hello, Malcolm;

you wrote:

All the posts are ok.

The connector type is almost like a millipede looking from top. Very fine gold connectors in half circles.

Two nuts holds the board down firmly over the connector.

That's good info. I have one of this millipede-like (mine haven't walked alway so far...) zebra connector. It's one of the best for connection, but it takes a lot of care to be kept in perfect shape. If yours is fine, better.

Are you saying the lcd module itself decides when to shut down the machine? Thats wierd. But if that's true then that would perfectly explain it. I was thinking the lcd module can't shut down the machine - therefore problem is not in display connector. - Wrong.

What really happens is that the calculator's CPU monitors the LCD state. When the LCD signs what I call "idle state", the CPU shoots itself down. There is a terminal used for this purpose, and as D.B., I sometimes cannot be confident about my bRAiM existing data. Anyway, if you slightly swing the calculator's case and and the display goes fine and the idle condition happens after about ten minutes instead of six seconds, than be sure you have a bad contact somewhere, and finding it is the major task.

I'd find someone with the skills to resolder the LCD's connections. One of our contributors in here resoldered the same terminals in his faulty HP41CX, and it's working fine.

The only precaution that must be taken is to connect battery terminals to the soldering iron's metal body while doing the job. You may remove the mainboard, the millipede connector (if you are not so confident, keep it in a closed box... kidding, I could not resist!) and take just the upper half of the calcualtor's case. Please, take care with a small plastic "stick" over the top of the LCD's assembly. It serves to keep it in place and to make things difficult to dust and dirt.

Hope this helps a bit more.

Success. and keep posting, so we can guide you better.

Luiz C. Vieira - Brazil


#8

YES YES YES

Thanks heaps - that was it.

I would not have got that without your help.

Display is now good and turn off time 10min

Thanks Malcolm

#9

malcom; try those jumpers. i had one with 2 of 3 of your symptoms and it was that. - d


#10

To db,

Jumpers? do you mean the lcd display connector wires?

Thanks Malcolm


#11

malcom; you are forcing me to use my memory and that chip is about burned out.

on one type of old 41 there are a bunch (13 to 15 or so) flat-ish wires between the bottom of the screen and the pcb, all in a row and out in the open when you take the back off. if this is the type you have then do like luiz said: take a sewing needle and gently lift each of those "jumpers" at each connection. we believe that one or more will be sitting in place but that the solder has come undone. that is why the screen may work if you twist the calc; you twist it into good contact.

if you find a loose one: there is no need to put more solder on the joint, just apply a bit of flux to the broken joint. hold the jumper down tight with the pin and use a real small tiped soldering iron. give it a little heat then blow on it and let up on the pin. try to lift it with the pin again. if the jumper isn't soldered down then give it a bit longer of a jolt with the soldering iron and test it again. keep trying longer times till the joint holds when you test it or till your 41 lies in smoldering ruins, whichever comes first.

this is common and it's the easiest to fix problem so hope like hell that it's whats wrong. - d


#12

Yeah,

That was it. Perfecto.

Thanks heaps for the help,

Malcolm


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