Re: HP-33E Parts



#3

If you did not get the power connections to the right place you can easily wind up with a bypassed power switch.

In the first HP38 that I fixed because of a dissolved flex circuit, I first wired the power and ground signals to easy to get to places on the LED circuit that seemed to buzz out to the flexprint... only thing was the power switch was on when I buzzed the connections.

Turns out the LED power connection is switched (obviously) and the machine would then not turn off. I then turned off the power switch, did some more buzzing and found a place to connect the power wire to. You can get to all three connections in that little window in the case above the PSU card, no need to take the unit apart. It is still easiest to wire the ground pin to the LED board though.


#4

YEs, the battery voltage and ground do go to the display module. Partly because the low battery circuit is inside the display (!). And possibly there's some driver circuitry in there as well.
As regards connecting wires to replace the damaged flexiprint, I prefer to connect all 3 wires to the PSU module (at least in the clip-together machines). It makes it easier to take the machine apart for repairs in the future, and it maintains more of the original design and construction.
I always take the machine apart to do the soldering, I am worried about melting the plastic chassis with my soldering iron. It's not hard to take a Spice to bits, after all.


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