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hp41c to hp41cv CPU swap
06-07-2014, 01:04 PM (This post was last modified: 06-07-2014 01:05 PM by GeorgeOfTheJungle.)
Post: #7
RE: hp41c to hp41cv CPU swap
(06-07-2014 12:32 AM)Massimo Gnerucci Wrote:  
(06-06-2014 10:52 PM)GeorgeOfTheJungle Wrote:  Also, the calculator now shuts down after 40 seconds instead of the usual 10 minutes...

For the shut down check C2 capacitor.

Grazie mille! Cristóforo Colombo, yes, that's it! C2 is a timing capacitor, and one that belongs to the display driver assembly by the way... so why the hell did they put it in the CPU pcb?

0.01µF is 10 nanos, 497pF is ~ 0.5 nF, the ratio is 10/0.5 = 20; 20*40s = 800s ~= 13 minutes.

I've checked it out with the scope. The green trace is (pin 4 of the display driver assembly) with the 41C CPU board , and the yellow with the CV CPU pcb:

[Image: attachment.php?aid=768]

Perhaps the dim display has to do with this too? We'll see...


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RE: 41c to 41cv CPU swap - RMollov - 05-29-2014, 06:19 AM
RE: hp41c to hp41cv CPU swap - GeorgeOfTheJungle - 06-07-2014 01:04 PM

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