My neck discs are about to curtail my playing around with this very stubborn
receiver for the evening (I'm hoping the doctor's fix on Friday works better
than my attempts at fixing this receiver!).
I plugged in my junker T-4XB this afternoon and hooked it up the the R-4A. Did
it for a couple of reasons: wanted to see if the T-4XB put out anything (it
didn't, but had idle current) and wanted to see if the low-level stages -
including the PTO - worked. They did and the receiver sounded beautiful just
like with my T-4X when it is controlling the frequency.
OK, I thought, time for the PTO transplant and I can finally call this thing
fixed. Wrong! With the PTO from the T-4XB now living in the R-4A, it sounds
as dreadful as with the other PTO.
There is a small board near where the wires from the PTO come through the hole
in the chassis. I have noticed previously that the signal connection from the
PTO to this board is just a piece of stout hookup wire with a sleeve around it.
First of all, I'm wondering if this is right - even though the schematic
doesn't define the connection from the PTO to this filter board as having to
have shielded cable. Second, when I started moving this board around with the
scope probe, the frequency warbled, chirped and jumped around! There's a
filter on this board: an inductor and two kidney-bean SM caps. As I rocked the
board back and forth, I was able to change the frequency!
I removed the very stout (was the stiffness of a lead from a 1-watt resistor -
probably #18 buss wire) hookup wire and replaced it with a longer piece of #24
stranded (more flexible). This seems to have done the trick. There was also a
cold solder joint at the ground connection of the filter board. In spite of
Garey and I discounting that the whole PTO assembly being able to be "pulled"
this is starting to look like mechanical stresses either on the PTO assembly or
the filter board were causing frequency shifts as the whole rig heated up and
things started expanding at different rates.
I am NOT going to call this cured yet but I am getting tempted. Since I now
have an R-4B and don't need to put this receiver back together quite yet, I'm
going to keep it sitting here in "Ugly Configuration" for a few days with the
T-4XB's PTO in it and spend some time taking pics of the R-4A PTO to send to
Garey and Curt. The control for this experiment will be to return the original
PTO into the receiver and check that it remains stable.
Troubleshooting ain't always easy, but I always have a great feeling when I
finally fix something!
Steve Wedge, W1ES/4
"I can't complain, but sometimes I still do."
- Joe Walsh
If the above message appears, it came from Steve's Son of Laptop!
_______________________________________________
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist
