Tuesday, September 4, 2012
Technical considerations about Yaesu G-250
The indoor unit uses a hysteresis voltage comparator based on a 741 op-amp. The red resistor is the one who adjust this hysteresis. It is a 330K resistor. The solution is to replace that resistor with a potentiometer (330K or even 470K is ok).
Just set the potentiometer to a 330K value and look for a position where the rotator starts to oscillate. Then, move the potentiometer until the oscillation stops. Now play a bit with the potentiometer and the indoor unit's knob to ensure the rotator do not oscillate any more.
As a rule of thumb, you must be able to do (very) small knob movements without any rotor movement, this is, you must obtain a new bigger hysteresis.