Hi Stan, The CNT90 service manual is available online from Fluke for their PM6690 rebadged version and is identical to the original, a search on "PM6690 Service" will find it. The manual contains a brief description of the oscillator and a schematic showing both the standard and ovened oscillators, and as far as I can tell from my CNT90 all required components for the ovened oscillator circuit, other than the oscillator itself, are already fitted to the PCB so just adding an appropriate oscillator would probably be all that's required. The standard and ovened oscillator circuits are completely separate, with individual outputs feeding the counter circuit and with individual ON/OFF control lines fed back, which suggests that both oscillators might be able to co-exist with auto selection depending on what's fitted. However, the circuit description states that only one or other of the oscillators is fitted, and the same internal calibration procedure is used for both, so it may be necessary to disable the standard oscillator, probably just removing the crystal would suffice, but I've not checked this. Playing with this is another of those things on my eternal to do list but as I've always used an external reference it's never been much of a priority. The manual indicates two versions of the ovened oscillator in the parts list, without identifying either, but it should be quite straightforward to wire up sample oscillators for off board tests to confirm possible co-existence and appropriate EFC characteristics etc. Plan Z of course might be for anyone who's got a CNT90/91 with the ovened oscillator fitted to lift the lid and take a look:-) Regards Nigel GM8PZR
I have a Pendulum CNT-90 with the standard oscillator option. I notice that there is an open area on the main PCB where a higher stability reference would be installed. 1) Is it possible to install an aftermarket high stability reference oscillator into this stock CNT-90 and be able to use it? 2) If so, is it just a matter of soldering an appropriate OCXO module into the designated area on the PCB? 3) Will the CNT-90 automagically recognize it, or are there jumpers or other things that have to be done to enable it? 4) Any recommendations for a good, high stability reference to use? _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.