Need help, why my HP-41CV do not work?



#5

Greetings
I have two HP-41CV that not was used in the last 14 years, I placed the 4 N-cels 1.5 volt each in one of the calculators and it display "MEMORY LOST" and a sound but not do any more, I can not turn on or off and after some seconds display ">- " in program mode. The second calculator done the same but now not display anything. I not have the manuals. Please can somebody help me?
Regards,
Amedeo Muscelli.


#6

Hello; (where are you?)

Please, I did not spell check this post; forgive my mistakes... >-(

There are many reasons for this behaviour, but as you saw "MEMORY LOST", let's take it as a good reaction. The beep worries me a bit, but... <8-|

The best shoot would be DUST. Can you open the calculators?

After opening them, you should check for dust (mostly from leaking batteries, but as you mentioned they were stored, I guess the batteries were not in place. Is it correct? :-)). There is an assembly that contains batteries contacts and I/O access; this is the first one to be checked. Remove it and have a look in the contactcs made with the keyboard's PCB. If needed, use some non-agressive cleaner (alchool is an acceptable choice at first) and remove, carefully, as much dust as you can. Avoid excessive material, so it will not leak into the keys' contacts.

There are two basic types of 41's: one that contains a separate PCB with all electronics (some integrated circuits) except display drivers: they are named FullNut (or coconut) and, in this case, the PCB should be CAREFULLY removed and the contacts inspected and, if needed, cleaned. The other type is named Halfnut and does not have this secondary PCB. The single PQPF IC in the middle of the keyboard is the processor, as memory chips are built in the display assy (Wow! I learnt a lot reading the messages at this forum...). The halfnuts will not have other places to be cleanned.

BE CARE WHEN OPENNING THE CALCULATORS FOR THE FIRST TIME! The halfnuts have their beepers built in the botton half of the calculator's box, and the wires connecting it to the circuit are somewhat thin. Avoid tracting them! :-(

Job done, reassemble the babes and tell us the good news! 8-D

Success!

(If you have no good response at the first time, it is good practice to shorten the terminas of the two large electolytic capacitors, ALWAYS begining with the big one and then the smallest; this way, all previously trash stored in memory will be history, and your calculator will not be locked because of a software condition)


#7

Hello Luiz,
I really are confused, I opened both calculators, all the contacts are very clean, not have a minimal sign of leakage, stain or dust and are all very bright, I also tested the continuity, and all work well. I short circuit the capacitors and settle the circuit on a conductive foam to discharge any current remained. One of the calculators was repaired for the HP, 12 years ago, and worked well. Why now, after all those years, stored in a dry box and without the batteries it not work?
The other calculator was used a few times and also was stored in a dry and clean desk and without the batteries, when I put the fresh batteries it run, done a sound, displayed some things in the display ( "ggggggggggg" but sight turn ) and immediately not done any more.
I think, that electrolytic capacitors have made with aluminium and paper impregnated with a chemical liquid. May be in those years the chemical liquid is drying?
Regards,
Amedeo Muscelli


#8

Hello, Amadeo;

It is for sure possible. The biggest electrolytic cap is basically to sustain voltage drop so you can change batteries without loosing memory contents (MEMORY LOST). The other one I'm not sure about. You should also check for the keyboard itself; conductive dust in there will also freeze the calculator and will allow the repeating characters to appear, as you mentioned.

You see, I have the PCB for one 41CV that no longer workes. I don't know why, I tried everything for now. I'm just waiting for the time to mix its internals with an old 41C that barely works: it freezes, goes to MEMORY LOST everytime, sometimes running a program or an internal math function (the most time-consuming, like trigs, logs).

Our babes sometimes turn our night s into days... right?

Success, and sorry not helping that much.


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