HP 38C repair



#3

I recently repaired a 38C with a corroded battery connector
by soldering a couple of wires onto the circuit board and attaching them to a battery holder in the battery compartment. The calculator now runs on two 1.2V NiMH rechargeable cells. I now find that sometimes some of the display segments disappear (for instance, the top segment of every digit may be missing), but that I can make the display return to normal by squeezing or twisting the case a bit. Does anyone have any idea what might be causing this? Also, would it be fatal to use 1.5V cells?


#4

Older versions of the HP3xC and HP3xE machines were assembled with very few soldered connections. Instead the ICs and display pins were clamped againsta foam-backed flexible PCB using a plastic frame. And this design suffers from
bad contacts, causing faults ranging from missing segments to total non-operation.
Take off the back cover (ypu've already done this, right), and unclip the logic assembly from the top case (there are 3 plastic clips each side). Don't lose the keys, which are now loose
Then flip the logic assembly over (keyboard on top) and take off the metal clip strips on the 2 long sides. Lift off the keyboard/'PCB'. The display will probably fall off, if not, remove it.
Clean the PCB pads and the display pins with propan-2-ol (isopropyl alcohol) and put it all back together. That should fix the fault.


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