HP85 sticky keyboard

[Tony Duell]

> 
> I just got around to checking out a pretty clean HP-85 I picked up at 
> auction last month. So far it powers up and runs a simple basic program 
> I typed in.
> 
> I haven't checked out the cassette,  although it doesn't look too bad 
> either. The only real issue so far is a sticking keyboard.
> Before I crack the case and check it out, are there any pointers on 
> fixing the sticky keys, any caveats.

A handful of points, in no particular order.

Firstly, there's a minor 'trap for the unwary' in pulling the cover. Pull 
off the tape drive eject button first, then remove the screws on the 
bottom and lift off the case. It's almost impossible to do it with the 
eject button still in place.

When you've got the cover off, you'll see 2 screws behind the keyboard. 
Remove those, the keyboard then hinges up at the front. Unplug the 2 
tapewires from the CPU board (under the keyboard), then unclip the hinges 
from the base and remove it. The tapewires and hinge brackets come off 
the keyboard PCB in the obvious way.

The keyboard is similar to the one in the original TRS-80 Model 1, the 
VT100, some other HP stuff, etc. The keycaps pull off easily, the 
plungers and springs come out (well, the caps-lock one is more of a 
fiddle...). HP say you shouldn't refit plungers that you've removed, you 
should fit new ones. I've never had any problems.

There is a particularly nasty problem with these keyboards. The plungers 
split after a time, due to the fact there's the stem of a keyvcap forced 
into them. They then stick. I hope that's not what's happened to yours...

The 'assembly level service manual' for the HP85A is on the MoHPC CD-ROM 
set. This is acutally not a bad manual, it does include schematics. 


-tony