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Need Urgent assistance: Testing a crystal oscillator circuit

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d_enthusiast

New Member
Hi guys, hope you could help me....

How could I check if I got a good frequency response of my crystal oscillator circuit, i.e. 24MHZ mounted in my motherboard. I got the board powered up, only thing is that the oscillation I measured does not respond to the value of my crystal oscillator (100kHz rather than 24MHZ) whenever I check the pin 1 with respect to DGND of my crystal oscr. I used Lecroy and Fluke 45 multimeter (frequency measurement). I already tried replace the crystal but didn't work out.

How could I measure the correct response of the crystal oscillator since I am expecting good sinusoidal waveform corresponding to the crystal value?

Is this affected by the program of my PIC but I already tried to reflash the with MPLAB using the good firmware?

Please advise. Thanks...
 
When measuring signals at that high of a frequency you need to make sure to use a x10 probe, otherwise you load the circuit down and your measurement will be incorrect if it oscillates at all. A quick and easy way is to toggle a pin high and low with a set delay between states then measure the output with a scope or frequency counter. Say you have the pin high for 20 milliseconds and then low for 20 milliseconds. look at the waveform with a scope and see if the periods match up. It is very rare that a crystal oscillates at a frequency other than what it is marked.
 

JimB

Super Moderator
Most Helpful Member
The frequency measurement facility of a Fluke 45 is only rated to 1Mhz.
Attempting to read 24Mhz will result in a fairly random display.
You need a proper frequency counter or an oscilloscope.

JimB
 

RadioRon

Well-Known Member
You can check if the oscillator is running by holding a short wave receiver nearby that can tune to 24 MHz. If the oscillator is running, you should be able to hear a carrier with no modulation, perhaps a small buzz sound at that frequency.
 
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