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Raymond Del Tondo · 01-02-2017, 06:24 PM

(01-01-2017 06:46 PM)aurelio Wrote: the match is always lost

happy new year to everybody....

I plugged into a not working tall key a block, restored with the Diego's kit, but the calculator still does not show signs of life.
Cosmetically very nice, the calculator does not seems apparently to have defects, I tested by changing the parts, the CPU, the "golden" connector, and they work, the problem seems to be located in the part which contains the display and the keyboard.
Apparently nothing to be remarked ..no corrosions, I mean, on the PC board interruptions or not soldered points, nothing that I can see.

I'm scared to disassembly the keyboard and the display to investigate the "dark side of the moon", for the reasons I wrote in older posts: I don't want damage the display with the soldering iron.

Is there a method to check the display without disassemblying it, and to check the healt of the two toogle switches?

Happy New Year, too:-)

Normally there is no need to actually disassemble/dismantle the LCD, however the solder joints between the LCD and the keyboard pcb should be checked first.

I had several 1979 and 1980 HP-41C units where the solder connection of one or more joints between the LCD and the keyboard pcb was broken. On some units you won't see the broken connection on first view, since the foot of the metal feather hovers only a few um above the solder tin landing point, but with a magnifying glass and a small screwdriver, which you can use to gently press on the metal strip, you might be able to find 90 percent of the defective solder joints, and then resolder the ones in question.

If it still doesn't work, you could resolder the remaining solder joints.

And if it still doen't work, check and maybe replace the zebra strip between the CPU and keyboard pcbs, which is another common source of malicious contacts.

If it doesn't work after all this, maybe the LCD is defective;-)

As usual, soldering in this area should only be done using a suitable low power soldering iron for electronic gear.