Hi Steve:
THe PTO that I have worked on have a diamond shaped hole in the coil end
coverfor the back end of the brass shaft and are not tight at all.
Shaft just kind of rides there. However, ANY slight movement of that
end will cause a frequency abberation. If there is any type of build up
of debris or gunk there, or inside the coil between the form and the
metal slugs stacked on the shaft, it will make the shaft bump and create
a jump.
I generally pull the whole shaft assembly and clean it thoroughly with
lacquer thinner or similar--even some fine wet or dry 400 grit could be
used. Also clean the square hole well with some thinner or 99% iso
alcohol. What you want is a low friction dry sliding condition at the
back end.
Be sure the brass rod is not coming in contact with the housing and
there can be no relative motion between elements or shield back there.
I use a dry spray lube that is like graphite powder on the shaft but dry
works just as well. NEVER any type of oil or grease or non-drying
cleaner/lube.
Of course, any free play in the FRONT bearings or slider will do the
same. I assume you have cleaned and lubed and re-set the shaft end-play
bearing? THat adjustment is a hex thru the back end of the coil base.
It should be baled off and then adjusted in (tighter) JUST until there
is no endplay. The difference between good and poor on this adjustment
is a praction of a hex flat. Perhaps a couple of degrees on the set
screw. But it makes all the difference.
Hope this helps some.
I have completely field stripped several Drake PTO assemblies in the
last year and haven't lost a single patient yet! Just take your time.
Curt
KU8L
Steve Wedge wrote:
I pulled the pto out and removed the cover (of course, this meant
pretty much disassembling down to the chassis to get it out!).
There was no zener inside -it had been clipped out. I couldn't find
any obvious bad parts using a stereo microscope, so I re-flowed the
solder on the board wherever I could and I moved the external zener
onto the B side of the board and soldered it in.
It seems more stable but it's still jumping a little. I've noticed I
can get it to jump frequency when I wiggle the brass shaft that holds
the slug. It also jumps some when I wiggle the cover. How loose
should that brass rod be with respect to the hole in the end of the
coil? There's definitely some free play there.
Steve Wedge, W1ES/4
To be is to do - Socrates
To do is to be - Plato
Do be do be do. - Sinatra
All my computers have my signature with various pearls of wisdom
appended thereto.
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