HP Forum Archive 01

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HP-25 Repair Tiips Needed. Message #1 Posted by Tony Copley on 18 Apr 1999, 12:39 a.m. I’m looking for advice in repairing a HP-25. The PCB is covered with blue residue. What is the best way to clean the PCB and surrounding parts? I could use some tips on how to remove the circuit board that connects to the keys. I’m concerned about prying the board free, as it might damage the board. Thanks - Tony

Re: HP-25 Repair Tiips Needed. Message #2 Posted by Tony Copley on 18 Apr 1999, 12:45 a.m., in response to message #1 by Tony Copley A repair tip would also be appreciated. Thanks - Tony

Re: HP-25 Repair Tiips Needed. Message #3 Posted by DaveC on 18 Apr 1999, 7:39 a.m., in response to message #1 by Tony Copley The PCB comes away from the keyboard assembly easily enough, as does the LED panel from the PCB. I'd use Isopropanol alcohol and q-tips (cotton buds) or dilute bleach (then neutralise with bicarb) If you use the bleach approach use a hairdryer to dry. DO NOT get the LED panel wet. You cannot separate the keyboard from the shell easily, if thats where the verdigris is then come back for more advice.

Re: HP-25 Repair Tiips Needed. Message #4 Posted by Tony Copley on 18 Apr 1999, 3:54 p.m., in response to message #3 by DaveC Thanks Dave - I would like to separate the keyboard from the shell. The keys have a very stiff (little action) feel to them and the "4" key displays a 6. I wanted to see if there was anything I could clean up. Any ideas on how to tackle this one? Thanks - Tony

Re: HP-25 Repair Tips Needed. Message #5 Posted by DaveC on 18 Apr 1999, 4:59 p.m., in response to message #4 by Tony Copley I've never needed to separate keyboard from shell for verdigris removal; I might try agitating for a few minutes in dilute bleach (pressing keys while doing this) then bicarb then wash with clean water for a *long* time then dry. What I think I'm saying is that *almost* anything is preferable to taking the keyboard apart! It is possible, the chances of wrecking the keyboard are large. Remove the heat stakes - use a sharp knife to remove the 'overflow' of plastic (i.e. NOT the actual stake, just the excess stuff that is keeping the board against the stake). Wash as described. Reassemble and while holding the board onto the stakes, use a soldering iron on the centre of the stake to spread it. Be sure that the power and prog-run switch are assembled before you do this, there are few second chances. I additionally use a piece of foam rubber to hold the battery compartment against the keyboard PCB as heat stakes never fully reassemble! Good Luck, you *will* need it!

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