Posts: 1,162
Threads: 26
Joined: Aug 2005
There are 2 basic types of construction for the HP41 series. The original type had a PCB with the keyboard on it, heat-staked to the cover. The display module
was linked to the top end of this board by soldered connections. The chips (all pin-through-hole DIP packages) were mounted on a second board that was
connected to the keyboard assembly by having a connector clamped between the logic board and the keyboard when the case was assembled. Finally
a flexible PCB provided the battery contacts and module contacts -- it was folded round a plastic frame in the lower case, and
pads on the flexible PCB were clamped against the keyboard PCB when the case was screwed together.
The second type is called the 'halfnut'. It has one PCB with the keyboard
contacts on it. On the other side there's a single surface-mount chip which is the CPU. The
display driver bybrid also contains the RAM and (basic) ROM. The CX
models have another PCB mounted on soldered posts across the back of the CPU -- this board
contains the extended functions ROM, extended memory and time module (but I have been told that the ROM on the display driver is different between CX and other models too).
The first type of construction suffers from bad contacts (often due to cracked screw posts). Also, the first type was designed to be repaired by HP to component level. The halfnut versions have many fewer contacts and generally don't suffer from contact trouble
Offical repair, BTW, was limited to replacing the extra board (in the CX), or the complete top case if there was a logic fault.
Still, the halfnuts do still have the flexible PCB for the battery/module contacts, so it's worth cleaning the contacts on that (and the pads it connects to on the keyboard), and squeezing the foam a little to improve matters. If that doesn't help, there's not a lot
you can do without another machine to strip for parts in general.