I know, this is about as far from a K2 as one can get, but you guys are the only people I know who understand electronics.
I'm trying to diagnose and fix a Sony laserdisc player (the old analog 12" babies) that I've owned since new. The player worked fine until I didn't use it for a couple of years after I got Dish TV and a DVD player. The player will not provide a good picture but instead there is 'jitter' as if the vertical sync needs to be adjusted on the TV set. >From what I know of LD players, the laser pickup retrieves an analog signal that represents a complete picture scan/frame. The CAV LD format has one frame per track so getting a still image means just keeping the head on the same track and letting it read the same frame over and over. There is a servo circuit that controls the head position, and it looks like the head position is controlled by voltage instead of discrete 'steps' using a stepper motor. This brand of LD player had a reputation for developing such problems due to electrolytic capacitor failure, and that seems like what the problem is here. I'm wondering if a bad cap is letting a voltage vary sufficiently to allow the head to wander because I can't even get a good still picture and I can hear the head moving ever-so-slightly when the signal is bad (it is quiet during the few moments the picture is good). Or, if there is a cap to damp voltage swings that has gone bad. I've got the service manual and I've done a preliminary voltage check on the power supply and things look to be where they're supposed to be... so the problem has to be downstream. My next step is to try and look at the voltage coming from the head positioning motor on back to whatever controls it and see if something is bouncing around when it shouldn't be. I'm hoping that I can just tack-solder a discrete component across any surface-mount caps that might be bad and make the problem go away. It doesn't have to look pretty, it just has to work. I'm open to any troubleshooting ideas, and have the service manual in PDF format if anyone would like to look at it. I don't have the special service circuit boards or the service disc... but, hey, NASA went to the moon with less, didn't they? I do have a 100 Mhz scope and a good digital meter, and of course my trusty soldering iron, and thank goodness this thing has a lot of discrete components. Why am I posting here? Because building a K2 and fixing other radios has given me just enough electronics knowledge to be dangerous. It's all Eric and Wayne's fault!! - jgc John Clifford KD7KGX _______________________________________________ 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
