Clock replacement

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nad

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Joined 2009
#1
Another question for any helpers out there......

Does anyone know if it is common practice when fitting any type/brand of ugraded clock to remove and jumper the 2 associated ceramic capacitors leading to earth from the old oscillators legs and also remove the parallel/series resistor?

Thank you
 
#2
The original capacitors are there as load specified for oscillation at the particular crystal frequency. If you are injecting a clock signal there is no need for these components anymore. If you are making your own oscillator you will need proper support components for your new crystal, specified by the manufacturer. Often these values will need trimmed for Exact operating frequency, and using the wrong ones will send you way out of the ballpark.
 
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#3
Andrew Eckhardt said:
The original capacitors are there as load specified for oscillation at the particular crystal frequency. If you are injecting a clock signal there is no need for these components anymore. If you are making your own oscillator you will need proper support components for your new crystal, specified by the manufacturer. Often these values will need trimmed for Exact operating frequency, and using the wrong ones will send you way out of the ballpark.
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Thanks, great info. I'm fitting a diykits.com.hk clock and don't want to screw anything up. Do I remove the caps to ground and 'jumper' each of them (in point to out point on pcb) and just remove the resistor?


Thanks again
Ant
 
#4
I don't know what you're modifying. I can't even tell you which pin to tie the TCXO output to. You should have some info on the IC that you're externally clocking. The behavior (of a possibly disabled) internal oscillator will be described in the datasheet.
 
#5
Andrew Eckhardt said:
I don't know what you're modifying. I can't even tell you which pin to tie the TCXO output to. You should have some info on the IC that you're externally clocking. The behavior (of a possibly disabled) internal oscillator will be described in the datasheet.
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Sorry, its a NAD C515BEE and I didn't get anything with the clock apart from a simple schematic for populating the board.

Can't find anything on the old oscillator (WIN 16.934 MHZ (12PF)) either.

Thanks
 
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#12
I'd wipe both pins clean of passive components and inject at pin 23. Possibly the AND gate can tri-state allowing clock injection at the "output" (usually there would be a blurb about that in a real datasheet) but without more info I can't say. In any case nothing will break if you inject at the proper voltage at the input pin. EDIT: That other side of the AND gate is probably being fed by a reset control line, so you'd want to inject at the input anyway so that still works. I figure...
 
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#13
Andrew Eckhardt said:
I'd wipe both pins clean of passive components and inject at pin 23. Possibly the AND gate can tri-state allowing clock injection at the "output" (usually there would be a blurb about that in a real datasheet) but without more info I can't say. In any case nothing will break if you inject at the proper voltage at the input pin.
Click to expand...

Thank you, that's exactly the reply I was looking for. Just need to order the psu and off we go. I was waiting a reply as I accidently 'broke' one of the tiny ceramic caps and wondered if I needed to replace it, then find out what value it was (bit burnt), then order the parts...... etc etc

Thanks,
Ant
 
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