|I just fixed my HP-48G+ ...|
Message #1 Posted by HrastProgrammer on 12 Oct 2005, 8:03 a.m.
... and I am so happy that I must share this with the others.
I have one HP-48G+ which suffered a lot of very bad "maintenance" (multiple falling on the floor and some "beating") from one high school student (not from me, of course, otherwise it would be in a perfect condition). Many keys didn't work (especially ones which you need a lot, like ON, +, -, *, /) or, precisely, they work sometimes when you press the calculator hard beneath the display, around C key. So, I decided to see if something can be done regarding this because it would be a shame not to try to fix it these days when HP-48 is no more manufactured and every working unit is precious.
There are a few methods for opening a 48 on http://www.hpcalc.org/hp48/docs/opening as mentioned in another thread and I decided to try one which claimed you can open a calculator without damaging it and using only one tool (http://www.hpcalc.org/hp48/docs/opening/openhp48.zip). In short: if you carefully follow the instructions, you can open a 48 without a need for any drilling or something like that. You don't even have to remove the faceplate! I succeded to open it in about 10 minutes using just a simple kitchen knife. Of course, some patience is needed but if I was able to do it then anyone can do it because I am not known as a very patient man.
The result was a disassembled 48 with the upper part containing keyboard, display and PCB separated from the lower part containing battery compartment. The PCB is fixed in place with six of "something" (I don't know how they are called in english, maybe fasteners or something like that). One of these fasteners was very interesting to me because it is located almost right there where you have to press the calculator to start registering some keys. I thought it could be lose so I tightened it a little bit (just a little bit) and also tightened the others. You must be very careful not to scratch the PCB doing this. And to avoid static electricity, too. Then I partially assembled the calculator, put batteries and pressed ON. It didn't react but I reseted it through a reset hole and it started to work. I didn't believe when I pressed a few keys: they were working! Amazing! Then I assembled the calculator to make some other tests. I used it for about 30 minutes or so and it registered all keys.
Just for practice and curiosity, I decided to open it again. This time I separated the PCB from the upper part to see what is underneath and to clean some contacts if needed. There was some dust around the display connector and I removed it with a soft, dry cloth. After doing this, I fixed the PCB again in place (this is a little tricky) and reassembled the calculator again. If you are reasonably careful then there won't be any scratches on the calculator and you cannot even notice it has been opened. After putting the batteries back, ON+E test displayed OK-48. Then I installed all my HP-1XE series emulators (HP-11E, HP-12E, HP-15E and HP-16E) and used them for more than a hour without any problem. All keys functioned properly.
Of course, I must use the calculator for a few more days to see if this was just a momentary luck or a permanent solution but I am very happy to know that I can (try to) fix some of my three HP-48GXs in case they will ever show similar behavior. Next week my friend and I will try to fix his old HP-48SX with exactly the same problem.
Perhaps this experience will be useful for someone ...
Of course, I am not responsible if someone burns his calculator trying to open it.
Edited: 12 Oct 2005, 9:28 a.m.