Faulty fullnut 41CV

[Paolo Cipollone]

Hi everyone,

sorry to bring this up again (thanks Luiz, but no luck till now), but here goes, before throwing the darn thing out of the window for good :-).

My fullnut 41CV was functioning properly when I last used it perhaps two years ago. When I picked it up about ten days ago it showed the following:

the display is dim to begin with; the calc just 'fades away' (for lack of better words) after a while.

Of course tried three sets of batteries before connecting it to an external power supply. At 4,5V (nominal) it behaves exactly like it were on batteries; 6V (again, nominal) will restore the original LCD contrast, but the characters are superimposed with garbage. The card reader, slow on batteries and at 4,5V power supply, works perfectly. Replaced C1 capacitor; CPU board has been hard wired to keyboard PCB -no problems from that side.

Connection between batteries and keyboard PCB is strong and consistent. I've even re-done LCD soldering.

Any hint?

Thanks in advance,
Paolo

[Luiz C. Vieira (Brazil)]

DO NOT THROW IT AWAY!

I once repaired a faulty coconut by replacing the power supply IC, it got warm to the touch right after the calculator was turned ON and the LCD was also dimmed. Its code (please, look here) might be 1826-0953 or 1826-0566 - IC code is normally followed by RAYC8126 - depending on design specs. I remember reading that these IC's are hybrid, they use MOS and bipolar technology and have no equivalent to replace, only by another one.

Please, keep it as it is. When I repaired the one I mentioned (for a friend of mine) I kept the remaining board from the donor, which had problems with RAM chips. It is still a source of replacements, though. But I have no spare power chip anymore...

Success!

Luiz (Brazil)

Edited: 7 Sept 2012, 12:10 p.m.

[aj04062]

I have a 41C that seems to have similar but not exactly the same symptoms.

It will be working fine, then not turn on. Sometimes a shorting of the + & - terminals resets, but this very rarely works. I can't tell if is the reason why I got it to turn on vs re-inserting the batteries or if it is some other random event.

It has been disassembled and contacts cleaned and all look pristine.

[BobVA]

Last time I ran into this the problem turned out to be a faulty solder joint on the connector between the LCD/switch board and the main board. You might try touching that up, if you haven't already.

[aj04062]

Well, I took apart again, cleaned contacts and tightened PCB nuts further. Got it working again. I think I need to apply some DeOxit to some contacts as they seem to be loosing their shine very quickly.

Has anyone ever applied DeOxit to the keyboard to PCB contact with success?

[BobVA]

I had a similar problem that was caused by a bad zebra connector. Maybe recheck the solder joints and wires on your hard-wired setup?