On Sun, 14 Apr 2013 12:17:03 -0700 (PDT),
wrote:

Here are the Manuals for my model:
http://www.hougen.com/downloads/10904.pdf
http://www.hougen.com/downloads/misc...structions.pdf
http://www.hougen.com/downloads/misc...aded_spind.pdf

(...)

http://i290.photobucket.com/albums/l...ps466ba0d6.jpg
How do I know they are still good? (The rectangular brushes are about 1/2" x 5/8" x 3/16").

They look good, except for the left brush, which looks a little
chipped. Shake out the debris from the motor, and put the brushes
back exactly the way they came out. Then, put an ohms guesser between
the brush contacts. Leave the insulating caps off, compress the
springs with the ohms guesser probes, and measure the resistance. I
don't know exactly what resistance to expect, but my guess is
somewhere between 2 and 5 ohms. (I can measure a similar drill
tomorrow if you want). What I'm looking for is a resistance that is
much higher than the 2-5 ohms, which would indicate an open in the
rotor or stator windings.

Anyway, I put the drill back together and while progressively manipulating
the safety switch adjustment between power up tries I got to the point
where the drill would turn on, which it wouldn't do before.

Progress, I guess. Now you have an intermittent drill, instead of a
repaired drill. You should spend the time finding the culprit. The
cracked edge of the brush is an important clue. If the broken piece
somehow got wedged between the brush and the commutator, that would
produce a no motor run situation. Look for a corresponding gouge in
the commutator and clean all the junk out of the motor with an air
hose. Watch out not to get anything wedged between the outside of the
rotor and the stator. If there's some magnetized junk in there, make
a cardboard shim and push it out.

So I'm still at a loss as to what the problem was. I probably didn't
re-insert the brushes *exactly* the way I took them out and was
wondering if that might be the reason it is working now.

I'm about 80% sure that it's somehow related to the brushed. If you
put them back differently from where they were extracted, you run the
risk of either gouging the commutator, or wearing down the brushes
prematurely.

What other procedures should I undertake before I start re-flowing
solder on the control PCB? (Since I have to sell the drill I want
to be sure it is working properly).

Take digital photos so that you can put the mess of wires back
together.

Important: Looking at the age, my guess(tm) is that it's Lead-Tin
60/40 solder, and not the RoHS crap. Try a small piece of Lead-Tin on
a solder pad. If it turns dull gray and rough looking, it's the wrong
solder. It should be fairly smooth, shiny, and of course, strong when
done.

I can't tell for sure from the photos or manuals, but there appears to
be a relay in the circuit. If so, the contacts should be inspected
and possibly burnished. If severely pitted, replace the relay.

Can anyone tell me where I can find new brushes?

Google for "hougen 17621 carbon brush set"
http://etoolinc.com/p10267/Hougen-17621-BRUSH,-CARBON-%28PAIR%29/product_info.html
Please verify that the 17621 is the correct brush set for your drill.

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