+- HP Forums (https://www.hpmuseum.org/forum)
+-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html)
+--- Forum: General Forum (/forum-4.html)
+--- Thread: HP-48SX (attempted) repair by Ben Heck (/thread-17473.html)
Pages: 1 2
RE: HP-48SX (attempted) repair by Ben Heck - Han - 09-19-2021 01:55 PM
(09-15-2021 04:10 AM)Geoff Quickfall Wrote: Yep, it was a cringeworthy how not to do it!!!!!!!!!
Eric is corrrect, the best way is in through the front after you shave the two heat stakes in the battery conpartment”
Opening the HP 42S which is the same way as opening the stretch pioneers.
And here:
Article in HP solve
I'm a bit biased, but I think the best method is actually to "shuck" the HP48 (and Pioneer models). It actually leaves the calculator in the best cosmetic shape, and still retains most of the structural integrity as well.
Opening the HP48 (thanks to Kees van der Sanden who had the foresight to save this as a PDF; after I left JU, I had forgotten I had not made a backup of things I posted on my webpage)
RE: HP-48SX (attempted) repair by Ben Heck - Geoff Quickfall - 09-19-2021 03:14 PM
Hi Han,
Shucking is great until you run into the ‘differing manufacturing bell curve’. Some heat stakes are so stiff and mushroomed that they will not release. The case becomes deformed and fit and finish suffer.
The longer the structure, stretch pioneers (48 series) will suffer the most. So I will attempt a ‘shuck’ but when the calculator fights back the I resort to the overlay.
Now, the overlay removal method, once the bezel cleanup and flattening was perfected, for me, is much less stress (on me and the calc) that I just go to it without the shucking attempt.
Each to his own,
Best regards, Geoff
RE: HP-48SX (attempted) repair by Ben Heck - Jlouis - 09-21-2021 10:41 PM
Nice.
It reminded me when my son was only 4 or 5 years old and I was trying to fix one of his remote car toy, he said to me " dad, have you read the destruction manual?
I gave a big laugh!
RE: HP-48SX (attempted) repair by Ben Heck - Geoff Quickfall - 09-22-2021 06:23 AM
“ have you read the destruction manual? “
Excellent!
RE: HP-48SX (attempted) repair by Ben Heck - GreyUser - 09-25-2021 04:07 AM
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.
RE: HP-48SX (attempted) repair by Ben Heck - ijabbott - 09-25-2021 05:37 PM
(09-25-2021 04:07 AM)GreyUser Wrote: 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.
Whilst you have the case open, I wonder how easy it would be to fit a Schottky diode in series with the battery to provide some proper reverse polarity protection?
RE: HP-48SX (attempted) repair by Ben Heck - GreyUser - 09-26-2021 05:40 AM
A zener isn’t desired or needed. It was so problematic and a cause of warranty claims that HP simply eliminated it on all later model G/G+/GX models.
I suppose you could install a series Schottky diode for true reverse polarity protection and live with 0.3 volt drop. But, it’s not necessary as the power supply and processor survive reverse polarity of alkaline AAA cells.