Final update :-)
It's now working normally!
To sum it up, I got a cheap Alliance HD-73 at a hamfest that had a problem.
The rotor turns fine, but the needle on the controller never moved.
On inspection, I found a bad 4.7V zener in the controller. Scored a
replacement from a friend and swapped it out. No luck, no change.
More trouble shooting found two bad diodes where the pot leads come into the
controller. I found a couple of 1N914's in the junk box and swapped these
out. Now the meter works, but is horribly inaccurate.
Yesterday I got a couple more hours to dig into it. I put the circuit board
under the magnifier so I could see it (my vision ain't what it used to be...)
and spotted a resistor that had been pretty hot. I swapped out this 15 ohm
resistor and varified all of the other resistors and diodes checked OK.
Success at last! It now appears to be working normally.
So, if you have a similar problem with your controller, check the diodes on the
pot leads and go over all of the resistors on the circuit board.
And now that I know the workings of this rotator so well, I'm thinking of some
mods. I would love to have a digital display...
73
Dan
--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
former K9ZF /R no budget Rover ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
>________________________________
>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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