[TowerTalk] Problems with YAESU Rotor

[Don Moman]

Having repaired the G-400 control box several times for a friend, here are
my comments (and some current measurements)...

R1 and R2 are 120 ohm .5 watt.  The motor draws about 40 ma when working
(no binding etc) so that creates .2 watts thru either one of the
resistors.  If the motor binds/stalls or shorts, the current goes to 110
ma which means about 1.5 watts in R1 or R2. This is a significant
overload.  I've replaced them with 5 watt 150 ohm units from the junk box
and ran the unit with the motor shorted (clip lead) for several hours.
Warm but survived. Q1/Q2 actually showed very little temperature rise
during this os they are not being worked very hard. 

If the tower mounted pot opens (or the leads are off etc) the control box
will turn the pot motor to one end and then stall, and if left would burn
out the resistors. So if you just energize the control box WITHOUT the pot
in the rotor connected, you will cause either one of R1/R2 to deal with
1.5 watts, a 300% overload.  Not what I'd call an intelligent design. And
I never saw any warnings about this in the manual......

Any shorts external to the rotor would not cause R1/R2 to be damaged as
they are several levels removed from the output. However, anything that
causes the bridge balance to be upset enough that the motor/pot in the
indicator cannot find the null will cause the motor to stall out at one
end or the other. If you transmit and the indicator moves, you have an RF
problem. 

Higher wattage resistors prevent damage, but they are not the cause or
cure of the original problem. The unit I repaired ran many times on the
bench (using an external 500 ohm pot on terminals 2 and 3 to simulate the
pot in the rotor) from from one end to the other and the motor showed no
signs of binding. It only worked for a day or so when put back into
service before it started acting up (but didn't burn up this time) so I
can only assume there is a problem with the pot or cabling in the actual
rotor. And that's not a project for February in VE6 land...

73 Don
VE6JY

On Mon, 15 Feb 1999, Scott Bullock wrote:

> 
> Mark, those resistors serve no other purpose than to provide current
> limiting for Q1 and Q2, which drive the slow speed motor for direction
> control. These transistors are small signal to92 type rated for 1 amp
> each. The only way these could be burning up as you say would be for two
> things to happen, 1: there is something binding in the direction
> indicator, either with the motor itself or the associated direction
> potentiometer VR2 and this is causing the motor to draw excess current,
> or 2: the actual motor is drawing excessive current and is causing the
> resistors to drop excessive voltage/current thru them. It's possible
> that the motor is under-rated for the current that it needs, but highly
> unlikely, as the 800S, 800 SDX, 1000S, 1000SDX, and 2800SDX utilize the
> same basic circuitry for direction indication and again, I have never
> heard of this problem on any of these rotors, which we have sold many of
> so far. 
> 
VE6JY  Don Moman               email: ve6jy@freenet.edmonton.ab.ca 
Box 127 Lamont, Alberta        email forwarding: ve6jy@rac.ca
CANADA  T0B 2R0  
(780) 895-2925       


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