Hi Guys,
I have good news to report. I have the PTO back in the T-4XC and it is
working fine. It turned out to be the hardened grease in the PTO ball
bearings causing the chirp and warbling after all. It didn't seem to be
a plausible cause to me for the symptoms I was experiencing. But before
I started changing parts out, I decided to clean the ball bearings and
the drive screw and it did the trick. AS for the PTO not working after I
reinstalled it into the transmitter, it turned out to be an intermitant
connection on the center tap of the PTO coil. Gary told me to check it.
Visually it looked OK, but when I pressed on the connection, the
oscillator came alive on the scope screen. Gary is amazing he can repair
radios from thousands of miles away. So I cleaned up the connection and
reflowed it. It is back in the T-4XC and working great now.
In fact, right after I got everything back together I heard ZK2V on 10
meters running split. A perfect opportunity to test the Transmitter PTO.
He was calling for just EU for a while, but when he asked for USA I
started calling 3kc up. I got him on the 3rd or 4th call. That's a new
one for me. Niue, I think it is an island down in the south Pacific
somewhere. Not very difficult for me on the west coast but, stil a good
test for the PTO. This was only 15 or 20 minutes ago, he is still there
on 28011 if your interested.
Anyway that's the end of this adventure. You guys will hear from me
again next time I break something.
73,
Bob K6GGO
Hi Guys,
Here is an update on my T-4XC PTO adventure. I eventually removed the
PTO from the transmitter and put it in a panavise on my bench, powered
it up and listened to it on my TR-7 with a sniffer wire. While
monitoring the tone, I tapped on the rod that carries the ferrite
slug. It would make the frequency change and stay on the new frequency
every time I tapped it. As an experiment, I opened up the R-4C and
tapped on the end of the slug shaft on it. On the R-4C, the frequency
would change but always return to the original freq. To make a long
story short, I found hardened grease in the ball bearing races. I
cleaned the ball bearings, races and the drive screw with denatured
alcohol. The frequency returns to the same tone now every time I tap
it and the warbling is gone when I turn the knob. I was and am
convinced I fixed the problem.
Here is the part where Murphy rears his ugly head. I put the PTO back
together and reinstalled it in the T-4XC and
presto!!............what?.... dead silence. I used the PTO to control
the R-4C still ....dead silence. I checked power and ground it looks
fine but still, nary an oscillation from the PTO. So I unsoldered the
wires and hauled it's sorry a?!%#$ back onto the bench. Powered it up
and still nothing.
Obviously, I hosed it somehow during the re-install. I looked for a
solder problem around the output terminal it looked ok, but there were
a couple of strands of wire from the old connection that the solder
sucker (me) missed, but they weren't touching anything. Maybe they
were touching something when it was installed, I don't know.
At any rate, its dead now and I suspect a semiconductor. here are my
questions: (about time eh?)
I have the diodes in stock but not the FET or the buffer transistor.
If I have to make a Digikey (or Mouser) order anyway, maybe I should
just shot gun the thing and put in all new parts except the coils.
I also have a PTO from a parts rig that has issues. I would like to
rebuild it as well. Will I get into problems with tolerance stackups?
I suspect that is why there are "select at test" caps in there.
Can I replace the coax that goes from the PTO output to the wafer
switch with RG-174? (to give myself a small service loop, to make the
re-install easier)
If it turns out to be a cap, or if I shotgun it, is there a modern
replacement for those horseshoe caps?
Is there anything special about the temperature compensating caps,
like a backwards temp coefficient for bucking freq drift or something?
Is there an easy replacement for those?
Sorry for the long post about my epic struggle against the evil Murphy.
If the 49ers hadn't won, it truly would have been a lost weekend.
Thanks as always,
Bob K6GGO
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