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Re Dead G-5400B



Ron Long suggested I might detail the Uni_Trac system rotator
safety features.

Taking the azimuth unit as an example.

The microcontroller in the system decides in which direction the
azimuth rotator needs to move and sends a continuos stream
of very narrow pulses from one of its two pins related to right
or left. These narrow pulses  are fed to a retriggerable
multivibrator which will set its ouput pin high for as long as the
triggering pulses are applied. When the pulses stop the multivibrator
output remains high for a period of approximately 120 millseconds.
The right and left multivibator are cross coupled to prevent
simultaneous outputs being applied to the rotator.

In the event of a microcontroller failure,
rotator drive voltage can only be applied for 120 millseconds.

The instructions from the computer to the microcontroller are
delivered via an interrupt driven handshaken transaction. In the event
of a printer cable or computer failure the microcontroller's error checking
will not allow refreshing of the control data and the microcontroller
continues to honour the last good command sent to it , whether
the rotator was travelling to establish equality with the feedback
information, or was resting at a previous defined bearing., If
you want to use the manual controls under this situation you
have to manually reset the microcontroller which "fail safes" the
rotator routines.

The above protection does NOT assist if the feedback goes open circuit
or short crcuit.

My modification kit for the G-5xxx controllers apart from using
opto coupled triacs in lieu of relays, uses constant current methods
in the feedback arrangement. Only two of the wires from the feed back
 pot are used. (Outer leg and wiper.). If per chance the feed back
circuit is broken an error signal is generated  and sent to the
microcontroller
which immediately inhibits rotator drive commands.

While on the subject of Uni_Trac, the new  software realease due shortly,
will allow automatic reconfiguration of the shack's radios, convertors, etc,
according to the MA256 position in the orbit. Along with the
Full Doppler Tuning facility there really is not much for a guy to do.

Regards

Dave Lamont   ZL2AMD       www.qsl.net/zl2amd/
                                              lamontd@clear.net.nz



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