On Tue, Mar 8, 2022 at 03:14 PM, Jinxie wrote:
A bit of clarification is certainly in order at this point, especially given there may be people new to the thread who haven't read it all through.
So.... the LED loop lock indicators for PLL1 and PLL2 are both on and remain on as they should. There is no LED indicator for PLL2, however. So one has to check the point HUL2 on A10A6 to establish if that loop is locked or not. Zero volts on HUL2 indicate PLL2 is locked. However, the voltage on that pin is jumping all over the place, so there is clearly an issue with PLL2. I then checked the 2 inputs to the phase detector on PLL2 and they, too, are jumping around all over the place. Both of them.
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If 500kHz reference is not stable other input (feedback port) of the phase detector will not be stable either. No need to debug the feedback divider, 500kHz reference should be checked first. As for the 100MHz reference, isn't the 100MHz front panel calibrator output derived from the same VCO? If you connect a counter to the calibrator output, is it stable? If you have a scope with more than 100MHz BW (seeing only fundamental is OK), looking with a scope would work too.?
Ozan
