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HP Forum Archive 03

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HP-27 Power-on Problems
Message #1 Posted by vrollinger on 30 June 2000, 8:31 p.m.

I have an HP-27 that has a problem powering on. Usually if I just turn on the power switch, nothing happens. Sometimes if I leave the power switch turned on for several hours, a weird number will show up in the display; then if I cycle the power, it will appear to power up normally, but the memory will not work (RCL # always returns zero) and the summation and financial functions do not work. If I leave the calculator attached to the charger overnight, everything works fine. This same problem occurs with several different battery packs, and I don't believe the problem is either discharged batteries or the contact point with the battery.

It seems to me that there is a weak component in the calculator (a capacitor perhaps?) that needs to warm up for a time before the calculator operates normally.

Does anyone have any ideas or suggestions? Thanks.

Re: HP-27 Power-on Problems
Message #2 Posted by katie on 30 June 2000, 10:08 p.m.,
in response to message #1 by vrollinger

I'll bet is the main filter capacitor in the power inverter. I've seen several problems in the Woodstock series with this cap; sometimes it shorts out completely, other times it appears to work but only at higher temperatures (what's probably happening with your 27, from the description).

It's an easy replacement. The newer ones use 2 tantalum caps, the older ones use 1 electrolytic. You can replace them with either type just watch the polarity and use a high enough voltage rating. The value of the capacitor doesn't matter too much, anything within a factor of 2 or so will work just fine, but you may see a somewhat brighter (or dimmer) display.


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