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[Yaesu] Kenpro KR600RC (now Yaesu GR600RC) rotator controller

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Subject: [Yaesu] Kenpro KR600RC (now Yaesu GR600RC) rotator controller
From: Duncan Clark <drc@dnamp.com> (Duncan Clark)
Date: Mon, 11 Oct 1999 13:40:26 +0100
Hi Folks,

I have a problem with a GR600RC rotator controller. It's been fine for
the last 4 years up until a few weeks ago.

I've put the circuit diagram on www.genesys.demon.co.uk/KR600.htm


When I hold down the left or right hand button, the rotator turns fine
but the motorised indicator stays put until the rotator is say over 120
degrees from it's previous location and then the indicator slowly starts
to move. Upon releasing the appropriate left or right switch the motor
speeds up to it's (used to be) normal speed and moves quickly to the
correct indicator position. 

I've checked that the pot on the rotator is reading correctly for it's
position, measured at the control box. 

The motorised indicator does go to it's correct final position. 

Only if there is enough difference (>120 degrees) between the actual
rotator position and the indicator position does it start to move.

The voltage supplied to the indicator motor is very low when the left or
right switches are held down even at (<120 degrees). Release and it goes
up, hence the speed up. 

Superficially nothing looks burnt out on the controller PCB. 

Voltage at each Zener D6, D7 looks OK. Voltage on transformer is OK, on
and off load.

I'll build valve linears, antennas etc. but this circuit has me stuck.
My guess is that there is insufficient signal coming out of the OP-Amps
to drive Q1 and Q2 correctly. But where to look first. They are only a
741 and a dual 741 so I could remove and replace. Transistors again are
inexpensive so if I have to replace all it's not a problem. Just seems a
shame to replace all at once. I'd rather know which has gone off spec. 

Any advice/suggestions appreciated.

The problem with being on the cutting edge is that you occasionally get 
sliced from time to time....

Duncan Clark

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