|Re: 17 Volts -- Ouch|
Message #5 Posted by Viktor Toth on 4 July 2001, 1:51 p.m.,
in response to message #4 by Tony Duell
Yes, I was quite surprised when I measured the idle voltage myself, perhaps a few months ago. However, I didn't realize until I read your message here that the sense amplifier chip is actually exposed to this full voltage when no battery pack is present. Scary.
I wonder why HP did this. The sense amplifier in the HP-65/67, all circuits in Woodstock calculators (but especially in C models), readily friable by HP's own charger, sometimes all that's needed is for the battery to pop out by accident. It'd have been so easy to prevent this (correct me if I'm wrong but I think a simple Zener protection circuit could have done the trick, at a cost that's negligible considering that the machines themselves still cost hundreds of dollars.)
By the way, have you actually seen a dead sense amplifier? I have, occasionally, plugged in HP-67s without a battery pack, but I have yet to see a fried sense amplifier chip. Perhaps this one chip can actually survive the high voltage, or at least some limited exposure to it? (Wish the same could be said about Woodstock ROMs and CPUs...)