hp 48SX repair success!



#5

Hello All;

Coincidentally this post seems relevant to a few differing posts below. Lets start with the story! I purchased this at the auction site with the following seller description:

THIS IS A HP 48SX CALCULATOR POWERS UP KEYS FUNCTION THE ITEM NEEDS NEW BATTERIES.

Not letting the word “function” confuse an otherwise cryptic description, I purchased with a “buy it now” thinking “ it would make a good rainy day project. Well, it is raining and the package arrived this morning.

Totally non-functional with the original batteries of which one had leaked! After cleaning out the battery hatch and installing new batteries I turned the calc on and no response.

Well, I read a previous post which suggested the foam rubber pressure pad for the keyboard contact to PCB may have flattened or rotted. Pressing on the keyboard just under the lcd panel and above the A – F keys did return functionality to the calculator. Of course not good enough as my carpentry clamps are to large to use! I did the selftest for the keyboard and rom/ram and they both passed as long as I kept pressure on the keyboard/PCB interface.

So I soaked the calculator, upright in luke warm diluted vinegar/water solution with the LCD panel above the water line. Followed this by a sequence of soak, wash and rinse baths always keeping the LCD panel dry. I did this in the attempt to dislodge dust and clean away any chemicals left over from the battery leak.

I then dried the entire calc with the ram access panel and battery hatch removed in a drying box:

Picture of drying box, the hair dryer has 2 3 position switchs. Fan (off-low-high), heater (cold-low-high)

This did not fix the keyboard contact problem so next step was to open up the calculator. Using a few photo explanations I settled on opening the case without cutting or damaging the snap rivets. I carefully pried the case apart following the instructions.

After separating the case I removed the PCB by twisting the 6 tabs. This allowed me access to the keyboard foam, which I removed and replaced with a Mouse PAD foam cut to shape. Inserted this in the now empty slot, cleaned the PCB and LCD connections while I was at it. Then reassembled with the outcome shown:

The calculator is snapped back together and the "function"s have been returned. The case is in excellent condition and the surgery left no scars.

Cheers, Geoff

Edited: 1 Apr 2009, 7:07 p.m.


#6

Geoff, you are simply amazing with this projects. Ever thought of making it a business? You clearly have heaps of skills and talents!

congratulations again.

Cheers

Peter


#7

I must give credit to the excellent resource that this forum presents.

I have now restored 2 HP 67's, and a 65 for clients as well as 6 HP 01 so far. But this is a hobby, so not a business yet!

Cheers, Geoff


#8

You can take credit for others such as myself, who have figured out how to make repairs based on your assistance. I certainly would not have been able to repair the clutch on my HP67 without it. It now works perfectly. Thanks.

Michael


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