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My newly acquired HP19C seems to have died on me
12-16-2014, 06:57 PM
Post: #7
RE: My newly acquired HP19C seems to have died on me
(11-27-2014 06:47 PM)Katie Wasserman Wrote:  The stuck-on problem would seem to indicate that the print head driver has at least one bad transistor in it. According to Tony Duell's schematic the 19C uses a single chip transistor array for this, not discrete parts. But it should be possible to bypass the bad transistor in the array with a single NPN.

Hi Katie,

I finally found the time to play with the 19C. Thanks for all your help! It was a bad transistor. For what ever reason it had a base emiter voltage of 0.2 Volts. After replacing it with a BC817 I now have a fully working printer! :-)

Unfortunately the 19C now has another problem. While typing in numbers, funny things happen. The display suddenly fills with zeros for example. Or somethimes segments c, d, e and g are lit on a few digits.

It seems, at least judging by it's smell, the calculator has been stored in a very damp environment for some time. Maybe the components suffered from that.

Cheers,
Harald
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RE: My newly acquired HP19C seems to have died on me - Harald - 12-16-2014 06:57 PM



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