On 11/7/2015 8:25 PM, Jeff Liebermann wrote:
I just repaired an old MFJ-269 antenna analyzer. This time, the 4
diodes around the RF connector were NOT blown. Instead, it was crappy
SMT soldering for the components surrounding the diodes. The solder
joints looked ok before I resoldered them, but were obviously a bad
connection because several resistors just fell off the board when I
touched one end with the soldering iron, indicating the other end was
not properly soldered. With the resistor removed, the PCB pad looked
like it had never been soldered. If you don't have good soldering
tools, a steady hand, and a good microscope, DON'T try this as you'll
probably make a mess, as I did before I realized what was happening.

Because the various parts on the RF board were not originally making
good contact to the PCB pads, the calibration is off. The display
reads about 12% too high for impedance and dead on for reactance. I'm
debating if it's worth calibrating.
http://www.w8ji.com/mfj-259b_calibration.htm

Now working on an MFJ-259A, which looks like the usual blown diode
problem:
http://802.11junk.com/jeffl/MFJ-269-repair/


That's how I got my MFJ-259B, about 15 years ago, Someone at the local
ham club had a defective one, gave it to a fellow ham to fix, he
returned it saying that he couldn't fix it.
I told the owner, let me have a shot at it, if I can fix it I'll
buy it from you. It was "the usual blown diode problem:" I shocked the
owner when I gave him $60.00 for the repaired unit. I don't think he
expected me to contact him again.
Mikek