HP41 cv Problem



#7

Can anyone tell me what might be the problem when I have to apply upward pressure on the battery pack to get the 41cv to power up and when I release the pressure it turns off again?

No corrision on battery pack

Thanks in Advance.

Nitro


#8

It's almost certainly bad connections between the parts inside -- probably between the 'I/O Assembly' (the flexible PCB that forms the port connectors and battery contacts) and the keyboard PCB.
This has been covered many times here in the past, but basically you take the machine apart (the screws are under the stick-on feet), clean the contacts with propan-2-ol (isopropyl alcohol) and put it all back together. Remember that the 41 is almost all CMOS chips (and irreplaceable custom ones at that) so take anti-static precautions when you're working on it.

#9

Bad contacts due do dirt/corrosion on the battery contact accembly or (more likely) broken out screw bosses on the case back.

#10

I think the strip of resilient material that pushes the I/O block contacts against the PCB tends to get compressed in some revisions of the I/O block.


#11

Yes, that can be a problem too (the foam block gets compressed and the flexible PCB doesn't make proper contact).
When you have the machine apart, squeexe the front and back faces of the part of the flexible PCB that touches the keyboard PCB (around said foam block) so that it bulges up a little and makes better contact when the machine is put together. That normally cures it.
Do not pull the foam out. You will _never_ get it back in again -- at the factory it's fitted before the flexible PCB is wrapped round the plastic support -- and you guessed it, the flexible PCB is then heat-staked in place.


#12

Thanks to everyone for their help. One of the screws was broken and it wasn't clamping down all the way. A little small spot of super glue fixed it right up and I can still take it apart.

Thanks Again,
Nitro


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