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HP-48SX Repair - Diode - Printable Version

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HP-48SX Repair - Diode - aj04062 - 04-19-2010

I think I just did a stupid thing.

late last night I was trying to resurrect a 48SX that had/has a battery acid damaged keyboard.

I have a 3 cell batter holder to test the unit before putting the back on. I think I reversed the polarity of it and momentarily smelled overheating electronics before I pulled it. Prior to this, I did resuscitate the unit, but the LCD screen had lines (I hadn't tightened the clips).

Is it permanently dead? I've read doing this will fry the zener diode. Where is it? Can I replace it?

Re: HP-48SX Repair - Diode - Han - 04-21-2010

The zener diode is right at the positive battery terminal (looks like a Y-shaped SMD).

As for the lines on the display, if it's missing lines then you simply did not tighten the twist-tabs tight enough. If on the other hand you see garbled pixels then it's because your screen is no longer in alignment with the LCD connectors on the PCB. Just realign the screen until it is as close to center as possible.

Re: HP-48SX Repair - Diode - aj04062 - 04-21-2010

Can you suggest a way to test the board/display funtioality seperately from the keyboard? The previous owner let the batteries leak onto the keyboard. I think this is the source of the problem, but I'd like to isolate it.

If it is the problem , then I need to try and fix the keys. Looks like a pain to pull that apart.

Re: HP-48SX Repair - Diode - aj04062 - 04-21-2010

Sorry Han,
1 more question, Can I bypass the zener to tell if I cooked it?