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HP48GX Boot Loop - help
08-04-2022, 04:27 PM (This post was last modified: 08-04-2022 04:29 PM by wmundstock.)
Post: #1
HP48GX Boot Loop - help
Hi All.

Have anyone seen an old HP 48GX with a bootloop problem like this?
Any suggestions? Basic troubleshooting steps did not work.

https://youtube.com/shorts/gmMI6rGGFSU

What I tried.
Hidden RESET Button - turns the calculator off, then when I turn on it goes back into that loop.

After resetting I tried:
1. On + C
2. On + A + F
3. On + D

Remove batteries, etc all tried.. No luck.

Note how when I hold the on key, it speeds up the beeps. Almost seem like a short... maybe capacitor damaged?

Any advice is welcome!
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08-04-2022, 05:11 PM
Post: #2
RE: HP48GX Boot Loop - help
Possibly it has a bad RAM chip.
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08-05-2022, 10:19 AM
Post: #3
RE: HP48GX Boot Loop - help
I was given (for free) a HP48GX with the exact same symptoms. I also tried everything to get it working again but without any luck. Once, by changing the batteries (with another brand), I was able to get past the 'Try To Recover Memory' loop but got stuck again at the Home screen. After months of trying I gave up and decided to open it up.
Once opened, I realized that the previous owner probably left the batteries inside the HP48 because there was some battery corrosion which was almost invisible when closed. The biggest corrosion was near the negative terminal and it did attack the keyboard layers, resulting in a non functioning keyboard.
I'm not sure whether your unit has the same problem but maybe you can have a closer look at the negative terminal in the battery compartment and try to look inside the case for any corrosion.

Hope this helps.
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08-05-2022, 11:28 AM
Post: #4
RE: HP48GX Boot Loop - help
(08-05-2022 10:19 AM)Kiwi Wrote:  I was given (for free) a HP48GX with the exact same symptoms. I also tried everything to get it working again but without any luck. Once, by changing the batteries (with another brand), I was able to get past the 'Try To Recover Memory' loop but got stuck again at the Home screen. After months of trying I gave up and decided to open it up.
Once opened, I realized that the previous owner probably left the batteries inside the HP48 because there was some battery corrosion which was almost invisible when closed. The biggest corrosion was near the negative terminal and it did attack the keyboard layers, resulting in a non functioning keyboard.
I'm not sure whether your unit has the same problem but maybe you can have a closer look at the negative terminal in the battery compartment and try to look inside the case for any corrosion.

Hope this helps.

Thank you for the response. I did look into the terminals and there seems to be a little bit of corrosion, but its really just a little bit. I letf the calculator overnight on a silica gel and in the morning I was able to get past the boot loop, but I can see that it is randomly pressing the + key. In addition it seems to be operating a little bit slower than normal... I am thinking this is the symptom of the key being pressed non stop, or may be another key. Not sure...

I am now trying to flood it with contact cleaner + isopropyl and let it dry in the silica again. Maybe, just maybe, this could help.

I may try a few more things but in the end I may have to open it. Perpaps I can fix if I can see where the problem is.
I saw a tutorial on how to open without causing permanent damage here.
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08-05-2022, 12:22 PM
Post: #5
RE: HP48GX Boot Loop - help
Damn, I'm sorry. It's a nice calculator too.
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08-05-2022, 12:50 PM
Post: #6
RE: HP48GX Boot Loop - help
Unfortunately I think this is what happens to a lot of 48 models eventually :-(

I have a 48GX with a similar issue but the keys that are permanently on are 0 and/or dot.

Surgery is not for the faint hearted and is very risky.

I did see one article suggesting submerging the keyboard (not the display), without disassembling the calculator, in an attempt to clean and fix it but not sure about that. Maybe someone here has tried or can comment.

I have a working 48GX and wonder if/when this will happen...
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08-05-2022, 01:55 PM (This post was last modified: 08-05-2022 01:58 PM by wmundstock.)
Post: #7
RE: HP48GX Boot Loop - help
(08-05-2022 12:50 PM)dmh Wrote:  Unfortunately I think this is what happens to a lot of 48 models eventually :-(

I have a 48GX with a similar issue but the keys that are permanently on are 0 and/or dot.

Surgery is not for the faint hearted and is very risky.

I did see one article suggesting submerging the keyboard (not the display), without disassembling the calculator, in an attempt to clean and fix it but not sure about that. Maybe someone here has tried or can comment.

I have a working 48GX and wonder if/when this will happen...

I am making progress. With the contact cleaner and isopropyl alcool I managed to get it turning on consistenly. It also fixed the reandom presses to the + key. Now the Alpha key is showing problems...

I am repeating the process now, with a lot, I mean a lot, of contact cleaner and then washing with isopropyl alcool. I am using a sringe to spray the alcool inside. I am doing this 1ml at a time, but I think i spent around 10ml of alcool already.
I can see that maybe submerging the keyboard on isopropyl could work... maybe even better would be to do that on one of those ultra sound washers... that could work well.

I do not know if it could cause any harm to the display, so I am avoiding the alcool into the display.
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08-06-2022, 02:45 PM
Post: #8
RE: HP48GX Boot Loop - help
if it helps, I have restored an HP-27s that had been flooded with water and then abandoned. I completely disassembled the keyboard and replaced the plastic rivets with micro screws. I cleaned all the various layers of film that make up the keyboard and restored the damaged tracks with a conductive marker. It worked well. I guess the 48 has the same construction philosophy. Find details in the forum if you search my posts.

Hardware: Hp48S - Hp50g (5x black + 1 blue) - HP39gII - Hp27s - Casio fx-CG50
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08-08-2022, 07:22 PM
Post: #9
RE: HP48GX Boot Loop - help
(08-06-2022 02:45 PM)franz.b Wrote:  if it helps, I have restored an HP-27s that had been flooded with water and then abandoned. I completely disassembled the keyboard and replaced the plastic rivets with micro screws. I cleaned all the various layers of film that make up the keyboard and restored the damaged tracks with a conductive marker. It worked well. I guess the 48 has the same construction philosophy. Find details in the forum if you search my posts.

Thank you for the suggestions.

I am saving the "take it apart" as a last resort in case everything else fails!

So far, with alchool + contact clearner + silica gel, it seems to be getting much better.
I got past the boot loop, and most keys are working perfectly. Only one key is failing but if I press it hard enough it works.

I will test it for a few more days, because I just took it off from the silica gel, not sure if I leave it out for long enough humidity could pick up again and start showing issues.

Only time will tell. Smile
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