HP 48GX Calculator


Hello All,

I have a HP 48GX calculator, but it does not turn on as it should. In order to turn it on, I have to press around the fifth key area and press the on button simultaneously. And the same procedure to turn it off.

When the item is on, I would like to know if there is a way to test for its full functionality. I have randomly tested it (mindlessly I would say) and all buttons work and it seems like some advance functions work.

I tried with pressing [on] and the fifth key on the top row, but it seems like the calculator needs to be in clear mode in order to test it, or at least this is what it suggesting because it thinks (think?!!)that I am asking for a specific function.

1.In short, do I have to reset the calculator in order to run the self-test function?
2.If so, how do I reset it?
3.Can I run the self-test under such circumstances?
4.How to run the self-test correctly?

Thanks all for any help!!


Hi, raze;

please, locate both [ ]C and [ ]E keys in the top key row. Use the following procedure so you can start a complete, "circular" self-test:

- while the calculator is ON, press the [ON] key and hold it down;
- while [ON] is held, press and release [ ]E;
- release [ON]](this is called [ON]/[E])
the calcualtor starts a self test that con only be interrupted with the sequence:
- press the [ON] key and hold it down;
- while [ON] is held, press and release [ ]C;
- release [ON](this is called [ON]/[C])
To activate the specific keyboard test, locate the [ ]D key in the top key row. Now, while the calculator is ON, do this:
- press the [ON] key and hold it down;
- while [ON] is held, press and release [ ]D;
- release [ON]; (this is called [ON]/[D])
- press [ ]E
When you perform the [ON]/[D], an interactive "step-by-step" self test is started. When you press [ ]E, you see:
| KBD1 |
| |
| |
| |
At this point you should press each key in the first row, left to right ( i.e. [ ]A to [ ]F), then repeat pressing all keys on each row, always left ot right, a complete row at a time, top to bottom.

I am worried about the possibility that you have a faulty (with a possible fissure) contact sheet (not a PCB, instead a "plastic", flex sheet with printed circuit) that seems to "retouch" edges when you press the mentioned area.

Hope this helps. Let us know wht happens.

Cheers and success.

Luiz (Brazil)

Edited: 15 Apr 2004, 1:19 a.m.


No need to do anything before for running a self-test, although of course it will clear your stack, local memories, and so on.

The repeating self-test should run if you press and hold [ON], press and release [E], and release [ON]. To get out of the self test, you'll need to force a warmstart (system halt).
To do the warmstart, press and hold [ON], press and release [C], release [ON]. Or you can force a warmstart with a "paperclip reset". On a 48G series, the reset hole should be under the upper right foot. Remove the foot, and you should see an R next to a hole. Insert something like a partially straightened paperclip straight in until it stops, I suppose a half inch or so, and remove it.



Thanks Vieira and James for your help.

Performed your suggestions, and it seems the machine works accordingly.

It displays:
1. OK-48
2. KBD1 OK

Does this mean that the machine is OK?

However, in order to do the self-test, I had to press around the fifth key to make it work. I had to press around the fifth key, not the button. This mean press around the plastic case.

It seems like the [on] button does not work properly, but when pressing [on] and pressing around the fifth key, it works perfectly. The same procedure I have to follow in order to turn it off or turn it on. The arrow key and press around fifth key and press [on] to turn it off.

In short, pressing the fifth key takes precedence for all other functions except when the machine is already on. Unless there are specific functions that require the [on] key except for turning it on,off and self-test procedures.

Any indications? Does it worth something on eBay? I will auction them next week if possible.

Thanks a lot for your help.
Greatly appreciate this board.
BTW, the "around fifth key" I learned in this board also =)


What about CANCEL and CONT? Do you have to use the same technique to get them to work?

By "around the fifth key", do you mean "on the face plate near the [E] key"? I'd suspect a poor internal connection. Maybe it could be fixed, if you care to take it apart and do some repair on it. As for eBay, I don't know how much the 48GX has been going for lately. If you were to offer it for sale, you'd have to make it clear that it has this defect.


Edited: 15 Apr 2004, 6:30 a.m.

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