Posted by
Don Wilhelm-3 on
Feb 02, 2007; 4:54am
URL: http://elecraft.85.s1.nabble.com/Transmitter-alignment-tp443420p443424.html
Jeff,
You may be chasing a 'ghost' - in other words, that 'short' to ground may be
present at DC but not at RF.
Remember that the relays latch, and the armature will be connected to pin 7
for the band that has last been selected. Going further on that vein the
relays shown on the left of the LPF will also have continuity from pin 3 to
4 for the last selected band.
What all that means is that the DC resistance will be close to zero from R67
through the LPF coils and relay contacts and then through the output winding
of T4 (which has the #4 lead grounded). So at DC, the resistance will be
close to zero through that path - at RF, the reactance comes into play and
will not be zero ohms impedance. For DC resistance measurements, R67 and
R68 are effectively in parallel.
So, bottom line, look for your problem elsewhere. I suggest that you build
the RF probe if you have not done so already and go through the steps
outlined in the Transmitter Signal Tracing section of Appendix A in the
manual. That should identify the stage at fault. Once we know which stage
is at fault we should be able to easily localize the failure to the
component level.
The most likely cause of failure is a soldering problem, so check the
soldering carefully (several times). Unsoldered connections can be elusive,
but they are the major cause of failure.
73,
Don W3FPR
> -----Original Message-----
>
> A little more info...
>
> Charles, N3EJS, was nice enough to point out to me that my
> strange resistor
> values of R67 and R68 sounded like they were in parallel, and had
> a hunch that
> pin 7 of the relays was probably shorting to ground.
>
> Checking this, and Charles was right on the money (thanks, Charles!).
>
> Now, the question of why the relays pin 7 was directly connecting
> to ground?
>
> I reset the relays by pulling the control board, powered up, and then put
> things back to normal. On "normal" power up (with the control
> board back in
> place) things looked good, no short on pin 7 to ground.
>
> However, as soon as I engage "TUNE" again, the short to ground returns.
>
> So, it seems as if I have a problem in the relay logic. Essentially
> the antenna jack is shorting, so I have a dead short across the
> output, it
> seems.
>
> Any thoughts on how to get the relay logic figured out?
>
> Thanks again,
>
> Jeff
>
> On Thu, Feb 01, 2007 at 09:20:27PM -0500, Jeff Kinzli wrote:
> > Alright, a little bit of an update on my problem...
> >
> > Gary at Elecraft gave me a list of voltages to check upon TX.
> >
> > Unfortunately, my scope is old and I couldn't get it to play
> fair, so the only thing I could really measure were DC voltages
> with my VOM. I'll probably go ahead and start putting the RF
> probe together sine my scope seems tired.
> >
>
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