Hp41Cx hard to wakeup

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Hp41Cx hard to wakeup

Postby Theo148 » Sat Dec 01, 2012 7:29 am

Hello Hp enthousiasts ;

I have a 1984 Hp41Cx fullnut whose wakeup is more and more difficult. I've read a lot of posts on the subject, cleaned the contacts of the keyboard and checked the battery contacts, all looks good.

However, after a ten minute of "sleeping mode", I have either or remove the batteries and put them back, or to have recourse to the procedure described by Hp (to press "on" 2 minutes without batteries and then the conventional hard reboot procedure) or to connect my optical wand and to scan something. In the latter case, the wakeup is immediate with no "memory lost" or even the time module reseted.

Extinction is immediate in all cases when pressing again the "on" button. I reject the hypothesis of the keyboard and think it could be the capacitor. What do you think?

Why the optical wand can put my HP41 out of its torpor ?

Thank you for your opinions and advice

Theo
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Re: Hp41Cx hard to wakeup

Postby Theo148 » Sun Dec 02, 2012 9:48 am

Hello to all;

I answer my own question I posed to the community, the solution revealed to me this morning after intense research in the "HP-41C/CV/CX Service manual", already available on this site for online consultation (or on CD).

After being immersed myself, I found at page 152, a digest of major breakdowns and parts to change or check first. The wakeup trouble evidently appears prominently.

Here, what is my surprise, alongside classics such as capacitor and diode ... the welds between the display and the keypad board are main source of this trouble. They had seemed good when I had done the visual inspection, but after testing the meter, one of them was just unsoldered and "curling" the circuit (so sometimes touch, sometimes not). I would add that ports 1 and 3, they recognized the devices connected (visible by Cat 2), were unable to "talk" with them properly (what I thought was a problem with the flex or dirt on contacts port which I had not cleaned).

After a small spot weld to restore contact, and a start "Hard Reboot", I have my "Lost Memory" for a time as desired.

And then miracles, my ports 1 and 3 work perfectly even with the barcode reader (one of the most demanding in terms of signal quality) and my 41CX responds to the first touch of the button On.

All this to say that if recalcitrant On key, and after eliminated the problems of corrosion and cleaned the keyboard switches, consider your test welds between the keyboard and the screen. The repair is fairly easy, and guaranteed results. After that, if the fault is not from there it is war surgery with changes in capacitors or diodes, but it is much more difficult.

Sincerely Yours;

Theo
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Re: Hp41Cx hard to wakeup

Postby calicobramble » Tue Jan 08, 2013 9:08 pm

Hi there, I know this thread has been quiet for some time, but I have a related problem with a 41CX, s/no 2407S41075.

It's very simple really - sometimes it switches on when I press the ON button, and sometimes it doesn't. Usually if I take the battery out and leave it alone for a couple of days it'll work the next time, but even that doesn't work reliably now.

Yes I tried new batteries. Hang the expense!

I've had the case open once already - I bought it s/h from the USA and when it arrived the the battery contacts had some corrosion but I managed to clean them before it got too serious, and was very pleased it worked OK at that time. But a few (3 or 4?) years have gone by and now the "may be I will, maybe I won't " problem has got to the point where I don't actually know when I pick it up if it's going to wake up or not.

Having had the case open once to clean the battery compartment - the screws and mounting posts were all OK so no surgery there - I don't want to push my luck more than I have to. Everything tells me you can only open these things up so many times!

And I realise that it's a bit of a silly question to ask - "is this the same fault as Theo describes below?" - but what's the feeling of the experts out there? Obviously I can't leave it as it is, so I'm going to open it up and take a look, but is this "welds" (soldering?) problem likely to be my problem? Doesn't sound too big a deal if it is this, and I'm willing to have a go. But if it's likely to be capacitors etc I'm feeling that I would do better to join the back of the queue with fixthatcalc.com (he's brilliant - he fixed my other HP41CV for me just fine) and not chance ruining the relatively pristine internals of this calculator by stripping those pesky liddle screws.

Any advice??

Best rgds

Simon
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Re: Hp41Cx hard to wakeup

Postby Garth » Tue Jan 08, 2013 10:09 pm

calicobramble wrote: feeling that I would do better to join the back of the queue with fixthatcalc.com (he's brilliant - he fixed my other HP41CV for me just fine) and not chance ruining the relatively pristine internals of this calculator by stripping those pesky liddle screws.

There's also http://www.vintagecalculatorrepair.com/index.php
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Re: Hp41Cx hard to wakeup

Postby calicobramble » Tue Jan 08, 2013 10:59 pm

Thank you Garth, he looks like one of the Good Guys.

Interesting resume on his life - do you notice how is it that the chaps who do the details stuff are often self-taught!

Look forward to fixing the problem with my lovely HP41CX

Rgds Simon
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Re: Hp41Cx hard to wakeup

Postby Theo148 » Fri Jan 11, 2013 7:48 am

Hello Calicobramble ;
I'm not an expert, but I can try to help you to determine if it is the same trouble or not :
- do you have a good signal on every ports ?
- when your Hp41CX refuses to wake up, can you switch the power on by repositioning the batteries (or pushing hard the On button) ?
If yes, it could be the same panne, or a trouble of the flex circuit. So, if you dont think you are able to replace the flex circuit (that you can buy on internet), send your calculator to a professional, if yes, open your calculator and start to make ohm tests.
Good luck
Theo
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Re: Hp41Cx hard to wakeup

Postby Mx_Serg » Fri Apr 12, 2013 3:42 pm

My situation was exactly described here. My opinion - after switch unit ON LCD drivers do not receive enough power (may be power tracks somewhere corroded, or the main chip became too hungry at startup :) ). While capacitors have enough charge - system will power on, but after some while calc refuses to light LCD on. If I press "backspace" after On - LCD sometimes become operational. Another way to successfully start machine - switch it off with "1" displayed (Fix 0,1 ). So, in this "mode" machine start without problems, even after hours of "sleep mode". Ok, I understand, that this workaround do not so impressive... But for now I did not find a better way to fix this. Of course, I already repaired flex cable after mass corrosion, fixed main PCB zebra contacts and replaced old capacitors. Before that machine was totally nonoperational. Now I have "partially ok" HP41 for a few bucks :) This is good, but, obviously, I want to have fully operational machine. My main suspect is weak "-" contact at the flex PCB. Any other suggestions?

P.S. When I press "ALPHA" after "ON" button - machine wake up at 100% cases... Strange behavior.
P.P.S. Thin textolite washer around right post (if looked from the rear side) solve the problem.

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