On Fri, 25 May 2012 08:04:09 -0700 (PDT), Peter Easthope
wrote:

I have 9 pin head from a Panasonic dot matrix printer. Soaking in
isopropanol freed the lower 7 pins but not the upper 2. They are
stuck fast in the brass plate which holds the tips in position. Even
several days in isopropanol fails to release these.

Brass plate? All the Panasonic print heads I've seen have a plastic
guide block. Care to disclose the model number? Better yet, a photo?

I'm thinking of removing the lower 7 pins from the head and then
trying to work 8 and 9 free. I wonder how difficult reassembly will
be. Does anyone have a clever solution?

You'll wreck it if you take it apart. Inside are 9 levers, which act
as a solenoid. It's these levers that are probably stuck. Rust is a
potential problem, which alcohol won't touch. Maybe WD40.

See photo of inside print head about half way down the page:
http://www.fastrepairguide.com/recommend/printhead-repair-guide/

Another possible problem is that the magnet has attracted some debris
or junk, which is now inside the printer and preventing the solenoids
from moving. Depending on vintage and model, your unspecified model
dot matrix print head is held together with either some hex screws, or
a snap on retaining clip. You should be able to take it apart. You
should be able to clean out any debris with a brush. Try not to
mangle the pins. The brittle pins don't bend much and prone to
breaking.

What is the technique for reinserting the thin plastic ribbon into the
connector on the head. The ribbon has a little flake of cardboard
glued to the end for reinforcement. Still, it seems so delicate that
I'm afraid of damaging conductors.

Just shove it in straight. If you must use pliers, wrap some
electrical tape around the plier jaws. Some force is required.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558