Yep - re-soldered everything around the gas regulator. Output looks solid and is 11V. Not sure about the tolerance of the zener inside this particular PTO, so I also tried temporarily putting a 10V zener from V+ to GND. With the voltage regulated, the problem persisted.
The thing that's really puzzling me is that the PTO that's currently installed was rock-solid in the T-4XB it was in, and I did test the operation (alas, the PTO control seemed to be the only function of that transmitter that worked, but I digress...). It's just unlikely (but not impossible) that a previously-functioning PTO would suddenly exhibit the same symptoms as the one that was replaced. Tonight's mission will be to power the PTO with a regulated 12V supply. I will test the one in the receiver first, with the remaining receiver power off, then on. If powering it externally does the job, I'll rebuild the regulated supply - which does have a diode and a 680k resistor in the cathode circuit. 73, Steve, W1ES/4 -----Original Message----- >From: Richard Knoppow <[email protected]> >Sent: Aug 24, 2011 3:30 AM >To: Steve Wedge <[email protected]> >Cc: [email protected] >Subject: Re: [Drakelist] I feel like a buzzard... > > >----- Original Message ----- >From: "Steve Wedge" <[email protected]> >To: "Ron" <[email protected]> >Cc: <[email protected]> >Sent: Tuesday, August 23, 2011 4:43 PM >Subject: Re: [Drakelist] I feel like a buzzard... > > >completely random. Gets worse if I tap on it, but then >again, I'd expect some reaction when tapping it. Now, I've >got to find some test leads. I'm going to turn my station >supply down to 11V so I can still run the K3 and will power >each PTO off this very stiff supply. > >It's now obvious to me that it's either the PTO (yeah, both >of 'em) or the regulated supply has issues. > >Steve Wedge, W1ES/4 > > If the PTO works in one transmitter but not the the >other that pretty much eliminates it. Have you made >comparitive voltage measurements in the two transmitters? >Gary said something about the source voltage for the zener >being marginal. The zener is fed by R-64 which in turn comes >from the regulated 150V buss. The voltage at the other side >of R-64 should measure very close to 10V and be very stable. >Check it using the scope while keying, it should not change. >R-64 is a wire-wound resistor. They are generally quite >reliable and do not change due to age or loading. However, >if one of the terminals gets flaky it can go up in value. >Its worth measuring and should be very close to the marked >value. If it has increased or if the solder terminals >between it and the zener have developed some resistanct the >current drop may be enough so that the zener can not >regulate. Tapping on the PTO may cause some shift in >frequency simply because things inside move a little. >However if tapping produces exactly the same sort of chirp >you get from keying it strongly suggests a bad solder joint >somewhere in the voltage line to the PTO. Trace this out and >poke around at it. But, check the voltage at the zener end >of R-64 to see what is happening there. > > >-- >Richard Knoppow >Los Angeles >WB6KBL >[email protected] > _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
