The most sensitive part is almost always the problem part! Try gently tapping other parts. I've often used the rubber eraser end of a pencil to make gentle pokes to determine which part is the most sensitive. Sometimes it's hard to tell!
One thing that can cause this behavior is marginal feedback. Crystals oscillate by vibrating mechanically. A small change by bumping a marginal crystal can start it, or the change in capacitance caused by touching the can. Make sure C84 and C85 are the right value parts. They control the feedback. Also be sure the diodes are in the right way around: D16, D17 and D18. C86 is important to keep the source of Q19 at RF ground. And, of course, you should confirm that you have 8 volts between ground and one side of C86 that doesn't disappear if you tap things! If it's your crystal, it could be an intermittent crystal but that's really, really rare! One problem people run into installing crystals is letting too much solder flow around the pins. The solder joint look fine on the bottom, but the solder flows through the hole (they are plated all the way through) and 'puddles' around the lead under the crystal where you can't see it! If the puddle is just tiny bit too big, it'll short the crystal to the case. It's often a 'cold', intermittent joint because the case wasn't hot enough to take the solder. The blob of solder around the pin is simply resting against the bottom of the crystal case. Try checking continuity from the pins to the crystal case while tapping/wiggling it to see if there's an intermittent. Keep in mind that most DMM's are useless for this purpose because they take a while to detect the short. If it's intermittent the DMM may not detect it. Many DMM's have a "continuity" check that sounds an alarm if even a brief contact is detected. The option is to remove the crystal and look! You'll need a good solder sucker (at least a spring-loaded unit like the Soldapullet Elecraft recommends) and take care not to put more heat on the leads than you need to. Ron AC7AC -----Original Message----- Hi everyone, Thank you all so much for all your suggestions and advice! It looks like I have some kind of intermittent fault in my PLL Reference Oscillator. I've retouched all the solder points in that area incase it was a cold joint, and after poking around at it for a bit it suddenly seemed to be working. Then after a few minutes it went dead again, no oscillation. So I poked the crystal X1, just kind of tapped it, and suddenly it's oscilating again. I've verified that there are no cold solder joints, the crystal is securely soldered and the case is grounded. After working on it for a while, it seems like the slightest touch or movement to the rig can cause the reference oscillator to start and stop. Does this problem suggest a failure within the crystal itself? Thanks also for the advice and feedback about the case bottom, I've got the feet parallel now and everything seems good there. 73 de Stephanie va3uxb _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
