Es un milagro



#4

Some of you may recall that I previously reported the demise of my HP-25C, or more specifically it's continuous (CMOS) memory. It had been working fine for years off NiCads, which I only charged outside the calculator. Then, suddenly, I could no longer store programs in memory or data in the registers, however, all other functions of the calculator worked fine. I figured that CMOS memory had finally failed, perhaps stressed by prior use of the AC charger.

I went about looking for a donor calc with CMOS memory, but then found another perfectly functional and cosmetically excellent HP-25C for a very reasonable price IMO, and so I bought it. Meanwhile, I opened up my old failed unit, and decided to give the main PCB a good cleaning in white vinegar, since there was some evidence of corrosion. When I re-assembled the calc and switched it on, all I got was some faint activity in the display and then nothing. I opened it up again, and noticed that a solder joint connecting circuit traces near one of the battery terminals was missing. So I fired up the soldering iron and laid down some solder to re-establish the connection. When I re-assembled the calc and powered it up, it was again working. But then came the astonishing thing, CMOS memory was working again! I stored and ran a short program, and stored and recalled a number from all 8 registers. Furthermore, when I switched the calc off and then on again, the contents of memory had been retained.

I don't know if there is any direct connection between the bad solder joint and the previous problem with CMOS memory, or if perhaps the cleaning had something to do with this, but frankly I am just happy to have my calc fully operational again. To me, it's simply a miracle.


#5

...pero si crees, no lo pruebas a me! 8^D

Saludos! (and congratulations for your HP25C!)

Luiz (Brasil)

Edited: 1 July 2010, 1:03 a.m.


#6

:)


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