24 Sep
2005
24 Sep
'05
7:27 p.m.
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