Voltage tuned xtal oscillator problems

Thread Starter

hafrse

Joined Jun 27, 2013
3
Hello,

I have problems with a voltage tuned 29Mhz xtal oscillator, it has no output signal. Checked the bias of the transitor, all ok, replaced thre transitor, varicap and the x-tal, still the problem exist.
It can be a component that went out of spec. I do not have schemtics but tried to drow the wiring of the oscillator and it is attached. also, desoldered all the caps and took there value by a capacience meter, but values below 20pf can not be measured.


My first question, does this circuit represent a complete 29Mhz Oscillator ? the reason I am asking is that I could have missed other components on the curcuit board beloging to the oscillator. L1 is 560nH.

Description of the circuit:

Input power is 10V
Bias input isalways -5.2.
Tune voltage is 3.72V when the instrument is powered on.
Any hints what I can do or test?

Thanks
George
 

Attachments

MrChips

Joined Oct 2, 2009
30,714
You can't voltage tune a xtal oscillator. That is what the xtal is for.
Unless you are referring to trimming to 10ppm.
 

Thread Starter

hafrse

Joined Jun 27, 2013
3
Hello,

I have problems with a voltage tuned 29Mhz xtal oscillator, it has no output signal. Checked the bias of the transitor, all ok, replaced thre transitor, varicap and the x-tal, still the problem exist.
It can be a component that went out of spec. I do not have schemtics but tried to drow the wiring of the oscillator and it is attached. also, desoldered all the caps and took there value by a capacience meter, but values below 20pf can not be measured.


My first question, does this circuit represent a complete 29Mhz Oscillator ? the reason I am asking is that I could have missed other components on the curcuit board beloging to the oscillator. L1 is 560nH.

Description of the circuit:

Input power is 10V
Bias input isalways -5.2.
Tune voltage is 3.72V when the instrument is powered on.
Any hints what I can do or test?

Thanks
George

Corrected circuit uploaded
 

Attachments

KL7AJ

Joined Nov 4, 2008
2,229
Hello,

I have problems with a voltage tuned 29Mhz xtal oscillator, it has no output signal. Checked the bias of the transitor, all ok, replaced thre transitor, varicap and the x-tal, still the problem exist.
It can be a component that went out of spec. I do not have schemtics but tried to drow the wiring of the oscillator and it is attached. also, desoldered all the caps and took there value by a capacience meter, but values below 20pf can not be measured.


My first question, does this circuit represent a complete 29Mhz Oscillator ? the reason I am asking is that I could have missed other components on the curcuit board beloging to the oscillator. L1 is 560nH.

Description of the circuit:

Input power is 10V
Bias input isalways -5.2.
Tune voltage is 3.72V when the instrument is powered on.
Any hints what I can do or test?

Thanks
George
With a varactor diode, you can only do a minuscule amount of tuning. However..for troubleshooting purposes, bypass the varactor and see if it oscillates.
 
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