Re: HP41CX - dead or asleep? Message #8 Posted by Tony Duell (UK) on 18 Sept 2001, 5:47 p.m., in response to message #1 by Brian
It is a bad idea to remove or insert any module when the machine is turned on. However, I've done it (by accident) a few times to one of my 41CVs and not done any lasting damage. However, it does normally 'crash' the machine.
I assume you've tried the standard methods of getting a crashed machine back to life. Start by holding down ENTER and prssing the power switch. That will reset most CXs. And try alternately pressing the CLX key and the power switch. Finally try holding down CLX while pressing the power switch. This will (should) cause a MEMORY LOST, but it might get the machine to work again.
If that doesn't help, take out the battery pack, peel off the feet and take out the screws under them. Take the case apart (the procedure has been given here many times in the past) and discharge the electrolytic capacitors by touching a 100 ohm (or so) resistor between their terminals. Put the machine back together and try again.
There are 2 types of HP41 construction. The older machines (fullnut) have a separate logic board with pin-through-hole chips (the large one is the CPU and keyboard scanner, there's a number of 8 pin memory devices (ROM and RAM), a 14 or 16 pin chip (I forget) that's the PSU circuitry and a 20 pin chip (in the CX), the real time clock). The display drivers are mounted direct-on-board at the back of the display. With these machines, HP used to replace individual components, and if you can get the parts (e.g. from other old machines), it's possible to do the same.
The later verson (halfnut) has everything on the keyboard PCB. There's a surface-mount chip at the front of the keyboard -- the CPU and keyboard scanner. Just about everything else is in the display module (ROM, RAM, display drivers, PSU). Halfnut CX machines have another PCB mounted on top of the CPU chip on solder posts. This PCB contains the extended RAM, extended functions and time module ROMs and the time chip. [Note, though, that the ROMs in the display driver are different between the halfnut CX and CV, so you can't upgrade a CV into a CX by adding this board. If you do, it'll find the time module but nothing else]
Anyway, the only official repairs to this type of machine are to replace the 'extra' PCB or to replace the top case (including the CPU, display driver, etc). It is possible to take the the machine apart, but it involves undoing the heat stakes holding the PCB to the top case, and it's non-trivial to get it back together reliably.
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