Sawtron/Kyodo KG105 drifting off Frequency

[kerinvalecomaudio]

Hi there
I have a Sawtron/Kyodo Kg105 and KG107 and after they are tuned up exact as the service manual says .for eg tx=476.425 mhz txco =12.00000 tp4=3.00 volt
If the unit is left turn off for a couple of hours when powered up the transmitt frequency is 476.426 or even 476.427 mhz .over time the transmitt will come down to 476.425 but then drift down to 476.424 or even 476.423mhz
the 12mhz txco drifts maybe .000001-7 mhz but the 7500hz stays stable on tp1 .tp4 changes from 2.7 volts to 3.7 volt
receive also seems to be drifting off frequency
can anyone sugest anything ?

 

[Lewish]

I am not familiar with those particular pieces of equipment, but have worked on or designed units for that frequency band.
The problem is in the frequency synthesizer. My first guess would be that a filter capacitor in the feedback loop has gone leaky and the synthesizer is not settling properly.
Hope this helps.

 

[kerinvalecomaudio]

thanks
i will see if this helps

 

[kerinvalecomaudio]

hi again,lewish
i am still haveing problems i also have coppied the circuit diagram for the vco and pll .please forward your email address to ianwells@tpg.com.au so i can forward the diagram though to you
thanks ian