Hi
I believe the screws loosen due to the thermal pads compressing not the
screws backing off. The lock washers should prevent the screws from backing
off and locktite may make the screws impossible to remove. Once the pads are
fully compressed the screws should not loosen, but it may take a couple of
times at 10-20 hour operation intervals to fully compress the pads. These
pads are not insulators, they are for heat transfer only and they have a
coating that slightly melts under high temperature. This coating fills all
of the gaps under heat and compression and forms a good thermal path to the
heatsink.
Sears sells a small kit of stripped screw removal tools. These tools bite
into the head of a stripped screw making it easy to remove. Screwdrivers
will ware out and start slipping in the slots. Mt favorite screwdriver is a
magnetic hand tool that holds the bits for power drivers. These bits are
much harder than most standard screwdrivers and can be easily swapped out if
they are worn. The magnet also holds the screw for starting or removing and
the handle of the screwdriver holds several different bits. The handle of
this screwdriver locks or it can ratchet in either direction. Most large
hardware stores carry these screwdrivers.
Don Brown
KD5NDB
- Original Message -
From: Bob Evans [EMAIL PROTECTED]
To: elecraft@mailman.qth.net
Sent: Monday, November 21, 2005 7:40 PM
Subject: [Elecraft] KPA100 stripped final's screw removal
Hi Folks,
This may not be a very high tech solution, but it got me out of a
perceived
pickle. I had stripped one of the screws securing the final transistors
to
the heat sink in one of my K2/100s. I was thinking how the heck am I
going
to remove a stripped screw in such a tight space?. A friend had
suggested
super gluing a Phillips screwdriver into the stripped screw. I tried it
and
the super glue didn't hold. Then I thought I could drill and tap the
screw
out, but I couldn't find a tap that was small enough. What finally worked
was simply to drill into the center of the screw until the screw head
detached from the screw shaft. It took a 5/64 bit. I had loosened all
the
other screws on the board and the board simply lifted away from the heat
sink when the screw head separated from the shaft. With the board
removed,
the screw shaft could easily be unscrewed from the heat sink and replaced
with a new screw. By the way, I turned the KPA100 board screw-head-down
when I drilled so there wouldn't be much of a chance for metal splinters
getting into the board. It worked!
I have always used a high quality #1 screwdriver when I tightened these
screws, but it stripped out anyway. I use my K2/100s exclusively for
contesting and have been finding I need to re-tighten those screws after
20-30 hours of full bore operating (100 watts, lots of CQs). Maybe a
Lock-tight type product is needed to keep the screws from backing out
after
thermal cycling, but some of you may have some advice whether this should
be
done or not. Anyway, in case you find your final's screw stripped, this
method worked for me.
P.S. I played around in ARRL SS SSB this past weekend. The K2 is a GREAT
side band radio too! I know, I know.I can get ejected from this reflector
for such heresy. ;-)
73,
Bob K5WA
K2s #4687 and #5119 in SO2R configuration
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