|[Problem solved] at least looks like it ;-)|
Message #7 Posted by Alexander Oestert on 19 July 2011, 5:02 a.m.,
in response to message #6 by Geoff Quickfall
thanks for the deoxit link. As I'm located in Germany the nearest source for it seems to be UK ebay, where I found some items.
Unfortunately the ON key is not my only problem anymore. After working well for a while, the display constantly showed NULL after pressing the SUM+ key and the 41 stopped working altogether. Now I get only a row of @ in the display when I reinsert the batteries. Or parts of @ characters or some strange signs scattered all over the place.
I performed ON <- resets and ON ENTER <- resets repeatedly, taking out and reinserting batteries with no avail. I cleaned (with isopropyl alcohol, not WD-40!) and checked the pressurized connector of the battery compartment as well as the foam connectors to the CPU board. They all seem to look ok. I could even measure connectivity through the foam connector to the printed leads underneath.
I think I will let the 41 rest for a while, maybe there is still some humidity inside the keyboard causing it to act up. The funny thing about humidity is that I found this document from HP
Reset the HP41
which is about possible static electricity affecting the calculator, that says one should increase humidity to solve problems... ;-) So I just soak it again and try to operate it under water! ;-)
EDIT: I didn't keep my promise to let both of us rest - me and the 41. I 'screwed' with it one more time and assembled it in a way I hadn't before. When I took it apart the first time, a brown plastic rail came off and I didn't see where from. As it had the exact length of the CPU board, on reassembly I put it under it on the side of the battery compartment. This thin plastic rail also has the exact length of the LCD display, which is where I put it now: in the gap between the top of the calculator casing and the LCD. And voilą, it's working. That rail probably screwed up the connection of the CPU board and the keyboard PCB, because it wasn't meant to be there. Can anybody confirm this? TIA
Edited: 19 July 2011, 7:10 a.m.