HP 41C calculator

I am not suprised. Most HP41 faults are just bad connections (either between the logic board and the keyboard/display or between the I/O assembly and the keyboard/display) and can be fixed easily. Corroded I/O assemblies due to battery leakage are quite common too, but they can be repaired with care and a fine-tipped soldering iron. IC failures are uncommon, but I have had the odd one. Sorting out logic failures is hard because the connections are made when the case is screwed together which means it's almost impossible to run the machine with the logic PCB exposed. HP used a special 'test calculator' at the service centres for this -- it consisted of a normal HP41 with the back case cut in half (exposing the logic PCB end) and modified pillars/screws to hold the logic PCB in place. I've never seen an official one, but making a clone was an enjoyable afternoon's work. The HP41 is still a very useful calculator. The 41C is the simplest model with 64 'registers' (a 'register' is 7 bytes...) of user memory, partitionable between programs and data. You can put up to 4 memory modules in it, each adds another 64 registers, but doing that uses up all the I/O ports. There was also a quad memory module which adds 256 registers using just one port. And then there's the 41CV which has the full memory built-in The top model is the 41CX. It's a CV with extended functions (string handling, etc), extended memory (the ability to save programs and data in named files in another area of memory) and timer (clock, stopwatch) built in _and then some more functions on top of that, like a simple text editor. Add on ROM modules include things like maths, stats, circuit analysis, structural engineering, thermal science, financial, etc, etc, etc. And ssytem extensions like extended functions and timer. And 'hacking modules' (third party code, although AFAIK HP always made the physical modules) like ZenROM which let you edit the machine's memory directly. Serious hackers even made ROM emulators (using RAM rather than ROM) so they could program the 41 in machine code. And then there's the HPIL module with its extension ROMs (extended I/O, HPIL Development, always called DevIL :-)) which let you connect this little calculator to a disk drive, plotter, thinkjet printer, RS232 interface, HPIB interface, video display, data logger, etc, etc, etc. And dedicated peripherals like a magnetic card reader, thermal strip printer, barcode wand. What do I have? About a dozen machines, mostly CVs, but the odd CX and the odd C (including a very early C with all the original bugs!), a couple of dozen modules, most of the peripherals, the machine code development tools, and so on. It's a great machine, and still very actively used -tony