hp41c to hp41cv CPU swap

[GeorgeOfTheJungle]

Hi,

Can I swap the cpu in my 41c:

   
   

and put in its place this cpu from a 41cv?

   
   

Are the pinouts compatible? And the LCD driver IC?

Thank you,
Jorge.

[Raymond Del Tondo]

(05-28-2014 09:00 PM)GeorgeOfTheJungle Wrote:  Are the pinouts compatible? And the LCD driver IC?

The pinout is the same. If the pcb is of the same thickness, you can just throw in the 41CV pcb into your 41C and try:-)

If the pcbs are of different thickness, there will be two flat plastic spacer rings in the unit where the thinner pcb came from.

[RMollov]

(05-28-2014 09:00 PM)GeorgeOfTheJungle Wrote:  Can I swap the cpu in my 41c:
and put in its place this cpu from a 41cv?

Easy:

[GeorgeOfTheJungle]

Cool, thanks!

Just one more thing: anyone here who can point me the clock's RC in these pcbs?

Thank you,
Jorge.

[GeorgeOfTheJungle]

Hi,

I've replaced the cpu pcb, and it works but not perfectly. With the CV board the display is a lot dimmer than before. I have checked the LCD voltages @ L1 L2 and L3, at the pins 17 18 and 19 of the display driver assembly: the CV board gives 1.04v, 2.0v and 3.14v whereas the C board was giving 1.1v 2.22v and 3.4v.



Also, the calculator now shuts down after 40 seconds instead of the usual 10 minutes...

Any ideas?

Thank you,
Jorge.

[Massimo Gnerucci]

(06-06-2014 10:52 PM)GeorgeOfTheJungle Wrote:  Also, the calculator now shuts down after 40 seconds instead of the usual 10 minutes...

Any ideas?

Thank you,
Jorge.

For the shut down check C2 capacitor.

[GeorgeOfTheJungle]

(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:



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

Cheers,
Jorge.