HP-48SX (attempted) repair by Ben Heck

[GreyUser]

There is no bell curve with this issue. It is 100% traceable to the year the unit was built. This date also uniquely determines where the unit was built so it all comes down to the date of manufacture, all decidable from the serial number.

It is true that the S and SX are not easily opened by popping the rivets. It absolutely can be done but sometimes results in a cracked case back or other problem but almost all are repairable. As mentioned, this is due to all S/SX having been made in the US and Singapore when the QC was much better and the posts are far better peened over and require more force to open. Those annular rings on the posts need to be removed/shaved down before reassembly as well. That’s a fact.

Another issue is that the ABS case material is losing plasticizer every year and therefore becoming more brittle with age. Since the S’s are the oldest, they are the most brittle and therefore the most susceptible to damage. Any unit stored at high ambients are prematurely aged and will be prone to cracking and breakage.

Another issue with the S series is that the keyboard backing plates are a much harder and brittle metal than the later G’s, the tabs will gouge the circuit boards and fracture easier than the later plates. This means you get two, maybe three attempts to twist the lcd tabs before they go bust. BTW, the same harder metal was used for all Pioneer keyboard backing plates, that never changed over the years.

The later G series units built in Indonesia will pop apart with zero effort and peeling thee faceplates on these units is far riskier than popping them open. I have popped more units apart than you can imagine and would put the problem rate at 1% or less and IMO peeling faceplates is time consuming and simply not practical, necessary or desirable. The simple take-away here is never start learning the rivet popping technique on a unit with a long, brown case. The older it is, the more skill (aka experience) it requires to pop one open without issue.

Oh, one last thing. Anytime you have an S/SX or early G series machine opened, be sure to remove the zener diode between the lcd boost mosfet and the boost inductor (the round blue blob). The original purpose was for reverse polarity protection but they don’t work because they will fail shorted when batteries are installed backwards and when it has failed, it will just drain your batteries in a couple days or less. Just cut the single bottom pin with a knife or small cutters and hinge up repeatedly until the other two leads fracture and it falls off.