I bought a used controller off of eham.net advertised as
working condition. It too had RF bypass caps on the
pot leads. There was an obvious arc track near this
stuff. Multiple components were blown up including
the zener and the meter. I suspect your unit was
butchered like mine. You will have to check everything
against the schematic. If there is a 1% resistor,
someone probably replaced the original. I don't believe
a 1% resistor is called out. I thought I could still
buy a new meter, but the one that "almost" fit would have
interfered with the transformer. It was a slightly
different version by the same mfr.
Most people selling on eham.net, etc are honest but
you never know.
I bought another controller listed as works but poor
condition. It worked perfectly and the condition was
quite adequate IMHO. I made near 1,000 QSO's on field
day with it, so I guess it works. An honest seller.
Rick N6RK
On 9/15/2013 7:51 PM, Dan Evans wrote:
Greetings group,
Sorry for the long posts, if you are not interested please delete now!
Still fighting with the HD-73 control box. I dug up a replacement 4.7V zener.
I replaced the zener, but, still no good. So.... I figure the next step was to
start pulling components off the board and testing each.
I noticed a ceramic cap and a pair of back to back diodes across two of the pot leads
from the rotator so decided to start there. (I'm no expert, but I'm guessing these are
to keep RF out of the meter) The cap looks pretty bullet proof, but the diodes are
tiny so I pull them all to test. One of the diodes was "open" and the other
was shorted. I have no idea what these were, but I had some 1N914's in the junk box so
I put them in.
And, the meter is working! Well, kind of, anyway... The meter moves now, but
it's no where near accurate. The needle will cross a full 360* within about
1/4 turn of the rotator. So, still more problems.
Did using the 1N914's change anything? The exact diode type is not marked on
the schematic, would this be critical?
I haven't started pulling resistors off the board yet, but that would seem to be the next step. Only one of
the resistors is a "high precision" type. I'm guessing the meter uses this as a
"reference". Would the zapped diodes have took out the resistors? They are not "open",
but I haven't confirmed the values yet. The resistor values are listed on the schematic, so they should be
easy to replace.
Am I missing anything? Yeah, I know it would likely be easier to buy a working
controller, but it's become personal now! :-)
As far as the contest goes, various other projects kept me busy all weekend
anyway so I didn't get to play with the September VHF QSO Party. However, I
did get my newly refurbished, antique, 17B2 assembled and put up on the tower.
Yep, it's an antique. It's one of the old ones with the 3 reflector elements.
73 all,
Dan
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