I have a Drake R4B that is having this problem with the frequency
shifting, drift and the PTO will stop oscillating. This happened after
I changed the dial lights.
I have cleaned the Yoke and the bar that the Yoke rides on with no
change. Also if I pushed on the end of the PTO it would stop the
shifting frequency and become stable for a few days or a week sometimes.
Today after looking at Ron's web site on fixing a PTO I just removed the
PTO cover. I had to take out a tube 12AX7 to lift the cover off.
After putting the 12AX7 back in, I turned on the radio and started to
probe the PTO circuit board and the most sensitive place was the
resistor on top, 6.8K ohm. This resistor is on the left side of the
coil. As I probed the resistor the PTO would stop oscillating with a
little more probing the PTO would start oscillating again.
Next getting out the DVM and probing the resistor when the PTO stopped
oscillating there were 10 volts on the ground side of the resistor.
Looking closer it looked like the soldering of the resistor to ground
was not complete. It had not flowed on to the ground pad. I also think
this ground pad is one of the grounds for the coils silver mica capacitors.
I heated up the ground side of the resistor and re flowed the solder and
made a nice shiney solder joint that flowed on to the ground pad.
I have heard no more frequency shift or drift or the PTO stop
oscillating when i press on the PTO or wiggle the PTO assembly.
I will do more testing and see if there are any more problems!
Thanks again
Lee KI6OY
P.S. I read each and every post. And thank you to everyone for the PTO
thread, it really helped.
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