Posts: 331
Threads: 47
Joined: Oct 2005
Electrolytic caps do have a limited life with storage rated at 4 to 8 years, but this is usually extended if they are powered up frequently but well under their max voltage rating. I have used many for 20 years with no problems and the failures will normally be seen as increased leakage and marginally reduced capacitance.
Tantalum electrolytics, the small bead type, can have a shorter life but are more prone to catastrophic failre, with high leakage currents. The failures are usually random, except when a badly manufactured batch has got out. If the circuit uses them at their voltage limit or with spikes going above their limit then the life can be very short (but I dont expect HP calculators to have this sort of design problem!)
I suggest you wait until you have a problem, but then check capacitor leakage if the problem could be associated with a capacitor.
The experience of others who have repaired these calculators will be the most useful info.
Did that help? I'm not sure.....
Posts: 572
Threads: 49
Joined: Jan 2005
This might explain your Abit catastrophe:
Leaking Capacitors Muck up Motherboards
Posts: 1,788
Threads: 36
Joined: Aug 2007
Generally, if it ain't broke, don't fix it. Most of the capacitors in HP calculators are under very little stress and/or their characteristics are not critical. The vast mahority of the caps are just fine and will stay that way for a long time to come.
There are two main exceptions. The first is a small blue tantalum cap used in the power supply filter of the HP65/67/97 card reader circuit. It develops a high ESR and quits filtering properly. The reader quits reading, but writes just fine.
The other is the 400 uF (approx) orange filter cap in the HP35/45/55/65/67/70/80 charger. I have seen a couple dozen chargers with it gone bad.
Other than these two caps, I have seen only a couple of random failures in several hundred machines.