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[TowerTalk] T2XD woes (too long - sorry)

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Subject: [TowerTalk] T2XD woes (too long - sorry)
From: Dick Green" < (Dick Green)
Date: Mon, 22 Mar 1999 11:22:48 -0500

I think the first thing to do is either verify that your meter is working or
get one that does. Then remeasure the voltages and resistances per the

Second, call Hy-Gain. They have good customer service and should be able to
answer your questions quicker than anybody else. I'm sure this is not the
first time they've heard about a short across pins 1 and 2 and/or reversed

The standard manual controller for the T2X will work in place of the DCU-1.
If you can borrow a manual controller from a friend you can quickly
determine if the problem is in the rotor or the controller. You can also
flip the brke wedge in and out independently of turning the motor, which
will let you more easily verify whether the wedge is moving or not.

I have the exact same rotor and controller as you, and get approximately the
resistance readings listed in the manual, plus reasonable values for cable
resistance. I'm using 250 feet of #14/#18 rotor cable and see about 1 ohm of
additional resistance on the #14 wire and about 2 ohms of extra resistance
on the #18. Even if your cable is short enough or heavy enough not to add
any measurable resistance, the readings should not be zero.

The reading across the pot (pins 3-7) definitely should not be zero. It
should be about 500 ohms. The reading from pins 1-3 or pins 1-7 should only
be zero if the rotor is at full CCW or CW, respectively, and the opposite
side of the pot would read 500 ohms in this case.

Those are the facts. Here's the speculation (made more difficult by the fact
that Hy-Gain does not supply a detailed schematic for the DCU-1 or the rotor
in the T2XD package):

1. If you burned out the pot, it seems unlikely that the resistance across
pins 3-7, 1-3 and 1-7 would be zero. More likely, one or more of these would
be infinite. This leads me to believe that you may have burned out the A/D
chip in the controller and that's where the two lines are shorted together.
This assumes, of course, that your meter is telling the truth.

2. Seems odd that you are getting 30 volts across the brake solenoid and
cannot hear the "twang" of the wedge retracting. It's kinda hard to believe
that a short across the solenoid would burn it out, but I'm no expert on
that. Seems even more unlikely that the motor windings would have been

3. If the wedge really is retracting and you just can't hear it, a
possibility for the motor not working would be a burned out triac in the
controller (the wedge voltage bypasses the triac.) A short inside the triac
could explain the zero resistance readings.

4. You may not be able to rely on the DCU-1 display as far as the rotor
bearing is concerned. If the A/D converter chip is blown, the CPU may just
read some unrelated value. Also, if the DCU-1 has lost its calibration
information, the bearing indication could be totally erroneous. The DCU-1
memory is only backed up by a capacitor, and if you unplug the unit for a
while after calibration, the capacitor will slowly discharge and the
calibration information will be lost. However, the rotor should still turn.

73, Dick, WC1M

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