HP-21 Disassembly Help...

[Geoff Quickfall]

There is stress on the original rivet with solder connection. The springs are strong and can deform the circuit board extrusion that have the contacts attached.


This fatigues the contacts at two points.:

1) the circuit trace in which case the contact circuit must be bridged from the contact point to a contact point further into the circuit board.

2) the solder joint at the contact rivet.

I check the circuit with a continuity checker to ensure continuity. This doesn't preclude the failure under stress. So I initially apply flux and re-solder the rivet solder joint and test. Then work my way back along the circuit trace.

The washer trick works but may have inadvertently repaired either the cold solder at the rivet or a fatigue crack in the trace close to the contact rivet.

Geoff