PLL Wax Woes
Almost everyone who owns a Kenwood TS-940, TS-440 and a few select
other transceivers or even the R-5000 receiver will have heard, or
experienced, the dreaded PLL wax potting curse.
The symptoms, in my case, were a dead radio. it would loose lock wan the
display would go blank.
Apparently, the wax does exactly just the opposite of what it was intended to
do; protect the sensitive tuned circuits of the PLL and other critically-tuned
sections of the equipment. Of course it took time for the hygroscopic
properties of the wax to show up. But it's a fact of life and its victims are legion.
Attempting the wax removal is not for the faint-of-heart or the inexperienced
technician. The PLL PC board is burried three layers down below the radio's
loudspeaker mounting assembly. You'll have to remove the loudspeaker
assembly, then the shielded digital board, and finally, at the bottom, is the PLL
board. There's a lot of sheetmetal screws and more than two-dozen PC board
If you are going to try this fix, be sure to put identifying marks on the various
male and female connectors so that they end up with the correct mate at the
end of the fun and games.
Here's one for the shielded sections that was poured full of wax. As you can see,
most of it is removed and we are down to the component level where very careful
scraping is required to remove the last 1/16 inch of wax.
This is the second shield on the PLL board. Note that the wax has been
removed to the point that the silkscreen of the PC board can be seen.
In areas where not all the wax can be removed, I made sure there were
clean "alleys" of wax-free space between components. hopefully, this
will preclude and conduction between parts when high ambient
moisture is present.
This is just one harness. I forget how many connectors
hang off it ... 14 maybe?
The digital board has connectors on 3 of the four sides ...
ya' better ID mark 'em!
The two necessary tools. You'll need a sharp pick or probe and some kind of
shovel or scraper device. This one has a 3/16 wide blade. That's just about right.
The whole ball of wax ... so to speak.
This is some of the evil stuff I scraped out.
Another important tool is a thin flashlight. This one is quite thin and takes
If you have good eyes, fine. If you need optical help, best to put on some
kind of magnifier. I bought some 2.5 diopter reading glasses that work
I don't suggest heating the wax, since all that does is make it gooey and it
tends to flow into worse places.
I also thought about a solvent, like acetone, but decided to use that if I
have to go back in there.
Results: The radio has been playing for about 4 hours. The shack is
warm, about 80 degrees and the humidity is pretty high - high enough to
be a bit uncomfortable. It's July 29th in Connecticut.
So far - so good.
If this thing survives tonight's CQ's and works for a few weeks without
sneezing, then I'll report back.
If it quits again, I'll also report back, but be warned; I may use some
words I learned in the Army.