Re: HP-45 calculator Message #7 Posted by Tony Duell on 4 Sept 2004, 4:28 p.m., in response to message #6 by David Smith
The advantage of doing component level repair is that you can often make one good machine out of 2 broken ones. In this case, it's likely that the A&R and RAM chips are good, so if you could find a machine with a fault in that area, you could use the parts from it to fix this one.
It is very unlikely the chips on the keyboard PCB have failed -- they're the display drivers (OK, the clock generator is in the anode driver, but since the machine does something, the clock is running). The fault is almost certainly on the logic PCB.
Since the machine powers up and does something it's unlikely the test points will be much help (the waveforms on them will look about right). So what I'd do if it was my machine is start by replacing the ROMs (starting with the one with the higher number, since I guess that appears later in the memory map, and it's likely the initialisation code, in the 'lower' ROM is intact). If that didn't cure it, I'd try the C&T chip.
I've desoldered and resoldered countless chips in HP handhelds without problems. It doesn't worry me at all (even on machines a lot rarer than a 45...)
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