Heyya, first time, long time etc I bought a Frequency Electronics FE-5650A rubidium frequency standard off eBay since they are cheap and look reliable and widely used. I saw that it was "OPTION CPOM", so I figured it was 15 MHz not 10 MHz (as I wanted), but the DB-9 pinout had a serial calibration interface that I was hoping to use. It powers up, and I get a good signal out of the SMA port, but unfortunately, it's both 15 MHz, _and_ I can't seem to coax any of the documented pins to give me a response. I figured that before I go further (start to pull out the PCBs and see where the DB-9 pins go), I figured I'd give the group here an email seeing if anyone else has experience with this specific unit, and how they calibrated it to 10 MHz. I keep seeing posts about it online, and it looks possible, I just can't quite get the right pins. Any pointers at all would be very helpful. Links to an album with pictures of the unit below. I don't mind continuing to chip away at blind reverse engineering this to see if I can work it out myself, but I'm really hoping someone here can either continue to give me hope (or a lead!) that it's genuinely possible with this specific unit, tip me off to another calibration procedure, or convince me i'm off the deep end :) https://photos.app.goo.gl/pBhr3uZEefWypjfdA Fondly, paultag