|Re: shorting HP-41 cont. memory capacitor|
Message #2 Posted by Ellis Easley on 19 June 2002, 4:00 p.m.,
in response to message #1 by Todd Koumrian
I opened up my 41C, which already has the feet off, and compared it to the service manual on the CDs, it is the same. I guess it is a "fullnut". If yours has a black border with rounded corners around the LCD, you have a "halfnut" (isn't it a CV? some are fullnut, some are halfnut). Someone will be by shortly to give you a better answer!
Section 2-33 (on page 10 of the PDF) says C1 is the storage cap, figure 4-6 (page 35) is an outline drawing of the PCB showing C1 is the largest cylindrical cap near the upper left corner, almost under the edge of the beeper, and table 4-5 (page 37) says C1 is 470 microfarad, 6 volt.
To open the unit, peel up the rubber feet to expose the screws. The two screws in front are close to the inside, the rear feet are about in the middle, slightly closer to the outside, under the feet. Note that the feet are actually two layers, the rubber is stuck to a thin vinyl layer which is stuck to the case (I know this is the case with Voyagers). Remove the four screws and the bottom comes off with the I/O and Battery block, giving you access to the PCB.
With direct access to the cap (without the diode in the circuit), the cap will pretty much completely discharge as soon as you connect the two leads with a piece of wire. Spend a few moments making sure you are making good contact to both leads AT THE SAME TIME! If you use a test lead with little clips, you can be pretty sure you have made contact. If you have a voltmeter, measure the voltage across the cap before and after. Observe anti-static precautions!