Disassembly of HP-19C

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Disassembly:
You have to (carefully) bend the power supply board. I will also suggest an alternative, but I haven’t tried it and drying may be more difficult.

The standard way: pull the bottom edge straight up, enough to just clear the two plastic pins. The thin area on the left side is quite long, so the amount of flex it can take is actually fairly high since it is distributed over a relatively long length and it isn’t that rigid because it isn’t very wide, either. At the same time you will have to lift the printer side enough to clear the battery compartment once both ends are raised, gently work the battery side up over the pins and towards the bottom edge. Your biggest danger her is actally breaking the plastic pin that holds the board in place. It can be repaired adequately if you breaki it, but it is much better not to do so. You will have to bend a bit more or less and maybe help the battery contacts come free of the case as they are not flat. On the printer side, once the board has been backed out a little, you’ll be able to have the printer side on to pf the battery compartment where you don’t need to monitor it. Sometimes you can work one corner/side out a bit more than the other so at least one corner will sit on top of the battery compartment; if you do it will be easier.

Sometimes at least one of the plastic pins are broken or weakened already. In that case you’ll have to glue it back. It’s actually easier to replace the board first anyplace the pin in place (if the bottom is not square, you should insert it in the hole in the PS board from the bottom (so you don’t break any part that is sticking out, after figuring the proper orientation. I then usually orient it after I’m sure things are working and glue it back by flowing cyanoacrulate UNDER the so board and holding in place. It’s good enough to keep the board locked in place from the pressure the batteries apply, but it’s likely to break again if you disassemble again.

Reassembly:
This first part of the reassembly is easier than the disassembly; just reverse what you did and things should pop back. Again, be careful not to put too much pressure on the plastic pins. See note above if you had to repair the pins. I find it’s the one on in the corner where the divide key is that’s usually damaged. Note that if there is a slight curvature to the board after all of this, that’s ok.

To get the case back together, first make sure the flex cable between the top circuit board and the keyboard is attached in all the places it should be to the keyboard. Then swing it downward (without detaching it from the keyboard so the bottom of the calculator (on the table in front of you in operating position), the to- circuit board will look kind of like a hand fan from the side with the keyboard on top and the front edge of the calculator as the “pivot” point.” In this configuration it isn’t too difficult to line up the two sets of pins (but you still have to be careful and it is easier if you have small hands). It’s usually easiest to connect the pins close to the display first, then worry about the ones along the side. If necesssry, you can remove the display to do that first fit together and then put it back in (but don’t forget!). At this point all of the electrical connections should be made. Remove your hand from between the keyboard and the cpu board (where it needed to be to do the above and snap the bottom edge of the calculator together. It will take a non-zero amount oof force to do this and there should be a fairly loud “snap” as it joins. You can then deal with the top edge of the calculator mostly by feel.

You may want to remove the printer cable from the power supply board; you may have to as it can slso harbor corrosion. Unfortunately it is a terrible design: The cable has a crease in it and the contacts in the connector are on the short tail end of the cable (so after the crease, electrically speaking. The cable plastic itself is reasonably robust but the circuit traces are not so strong and sometimes break over the crease. To remove the cable, look for some of teenix’ posts on the -97 printer. You need a thin shim (I use a piece of aluminum) you can insert into the connector between the connector and the folded edge (“short”) end of the cable. The shim needs to be the full width of the cable. You then gently pull out both together. You usually don’t need the shim to reinsert the cable.

You could try to just soak the ps board without removing it, but you won’t be able to inspect the underside of the board. It may also be hard to thoroughly dry the board. Make sure the printer itself doesn’t get wet.