Re: HP67 chips Message #22 Posted by Viktor Toth on 12 June 2001, 9:27 p.m., in response to message #21 by Tony Duell
22-pin chip is the ACT... yes, that's right of course. Neglecting for a moment what the acronym ACT stands for, I temporarily labored under the assumption that we have a processor _and_ an ACT...
Incidentally, this same chip I believe is also used in the HP-25, which does in fact have separate RAM chips, i.e., the RAM is not integrated onto the processor, so I think that pretty much confirms your guess: one or more of the ROM chips is probably a combined ROM/RAM chip. I'd suspect it's the 18-pin chip, because all the 8-pin chips have numbers in the same series as the numbers of the ROMs in the HP-97... of course, numbers mean nothing, and besides, the HP-97 Service Manual could be lying about the function of those chips, too.
The 16-pin chip is a 7-transistor array? I didn't know that. Mind you, that wouldn't stop me from using a transistor to substitute for a broken segment driver... in fact, I've done that before, although not in HP machines. (I have, however, replaced fried 4-transistor arrays in an HP-91 with discrete transistors. Worked fine.)
I love these old machines. For one thing, they are actually repairable, unlike those present day machines that require dynamite for disassembly, only so that you can then find a superfine PCB with a single blob of an SMT chip in the middle...
Thanks again for all the help!
Viktor
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