Hi, all;
based on what happened, I guess that this would be of interest for those who repair Voyagers and newer calcs. Having my bother in a rush (hollydays), he asked me to try finding what was wrong with his HP12C: it did not turn on. Fresh bateries, slight twist and voilà!
[ Pr Error ]'It's alive...' Then the problem: each time it was turned to off, it was necessary to twist it back again so it would turn to ON with a big Pr Error in the display. It was too fast to be a bad contact, maybe the internal capacitor itself was bad. After openning it up I saw one of the internal assemblies I was searching for: the one board only style, three batteries and two IC's, mainboard layout like the HP11C/15C. With this one, I have already seen at least three different HP12C internals with three batteries, missing only the one with flex circuit (earliest of them all).
Now the works: resolder all terminals in both IC's and components, because if comms fail between them two, I guess that it would cause a Pr Error as well. O.K., IC's terminals resoldered, turn the calculator ON and no way to start the self test. Awkward: keys in both right-side rows 2 and 3 generating similar codes. Press [1] and 4 appears in the display, press [2] and 5 appears in the display... either {+] or [-] generate code 20 in program mode. My conclusion: short circuit in row lines. Open it again and visual check: nothing. Clean all solder pads and... nothing. I decided to go for awkward tests and firmly pressed the processor against the m-board: calculator works perfectly fine! What to do? Surgery! I removed the IC. Look below:
I inspected the surface and it was not hard to see some green crusts over some golden-coated trails, suggesting some corrosive product or residual liquid was allowed to get inside the calculator. Unfortunately I tried to remove them prior to take the picture below, but some remaining dust can be seen:
I carefully cleaned the surface, removed all visible dust (I use a small lens) and soldered the IC back:
My brother is happy, and one other HP12C is alive again!
Cheers.
(to my three friends that have calculators with me: M.B. (41CX), R.T. (29C) and J.E.G.(25,41CV), please be sure that this experience enhanced my wish on having your calculators back to life... I'm regrouping and getting ready to attack!)
Edited: 27 Mar 2005, 10:54 p.m.