Re: 42s upgrade Message #9 Posted by Vieira, Luiz C. (Brazil) on 15 May 2010, 7:12 p.m., in response to message #8 by Paul Dale
Hi, Paul;
before going ahead with soldering, consider doing that WITHOUT batteries in place AND providing the batteries contacts are shorted with each other. I am sure this should be well known, but if batteries are in place no soldering should be performed because the chance of shorting active lines in the circuit (RAM chips must be powered if its contents are supposed to be retained, right?) and causing damage are big enough not doing so. Also, if the batteries terminals are shorted, remaining capacitor charge should be neglected and ESD would be avoided as well.
And before using a fresh new set of batteries, remember that their current capacity is the highest expected, so if you still believe that you may have shorted terminals, try with regularly discharged batteries first so they will not drive much current if a short circuit still exists. The worst scenario of using partially discharged batteries would be dimmed LCD characters and low battery indication, meaning that the calculator is probably working fine. If so, then go with the fresh batteries.
Last but not least, if nothing goes right, repeat the mantra: 'FIXTHATCALC'... 'FIXTHATCALC'... These HP42 beasts are stronger than they seem to be.
Success!
Luiz (Brazil)
Edited: 15 May 2010, 7:17 p.m.
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