SA Tektronix 492 - YIG oscillator - Page 1
Forum section: electronics / repair

author: memory58
author_rank: Newbie
timestamp: December 04, 2024, 04:46:05 pm
content: Hello,I'm new here.In the SA Tektronix 492 does not work the 1lo.I suspect the YIG oscillator.....Can someone please give me a useful tip?Thanks and Best regards

author: edpalmer42
author_rank: Super Contributor
timestamp: December 04, 2024, 08:01:42 pm
content: If you want good answers, ask a good question.Since you're new, what's your knowledge level? What test equipment do you have access to?Did this unit ever work or did you buy it in this state?What info do you have on this unit - service manual? - schematics? - web links? Yes, I realize the 492 has lots of info available, but most of us have neither the time nor the inclination to do legwork that you should do.What are the symptoms?What measurements have you made and what results did you get?IOW, how much effort have you put into this? Or do you expect us to do all the thinking and searching for you?*** End of rant ***Since there's no context for that picture, it isn't very useful. But, I see a couple of Tantalum capacitors that should be checked. Maybe a web search would tell you if the 492 has problems with Ta capacitors (hint, hint).I see a row of 5 pins. It's could be a trick of the light, but I don't like the looks of the soldering on any of them.I don't know if you're familiar with the basic operation of a YIG oscillator (hint, hint) but here's a random collection of info on YIG oscillators. There's nothing specific to the 492 but it will give you the basics.http://www.mediafire.com/file/6v0db7crbkbb943/YIG.zipEd

author: unseenninja
author_rank: Regular Contributor
timestamp: December 04, 2024, 08:40:15 pm
content: Quote from: edpalmer42 on December 04, 2024, 08:01:42 pmThey look like the tops of pins from a PCB underneath the top one coming up through sockets on the bottom.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 04, 2024, 09:55:14 pm
content: Quote from: unseenninja on December 04, 2024, 08:40:15 pmUnusual, but possible. Hopefully, someone with more knowledge on the 492 will comment.Ed

author: memory58
author_rank: Newbie
timestamp: December 10, 2024, 10:19:16 pm
content: Hello,thank you very much for the answers! The device worked for a short time, then the power supply went away...I was able to repair that... After that, no signal (amplitude) is displayed...And 1 lo output is empty. I have some measurement technology at my disposal, but I have to admit that I'm still a beginner when it comes to RF technology. I will take a closer look at the YIG documents and the service manual for the 492.Best regards

author: KE5FX
author_rank: Super Contributor
timestamp: December 10, 2024, 11:21:52 pm
content: Key point to remember: anything that shuts off the tuning coil current will keep the YIG oscillator from working. If you don't see at least ~80 mA going into the main tuning coil, look for the trouble on the 1st LO driver board.Usually they tune at about 20 MHz/mA, but this can vary. So the zero frequency point, near 2000 MHz, might be reached at 100 mA.Also, it's very easy to damage the SMA plumbing on the chassis underside. Don't overtorque the fittings!

author: edpalmer42
author_rank: Super Contributor
timestamp: December 10, 2024, 11:26:53 pm
content: Yes, that's the challenge. You almost need a spectrum analyzer to fix a spectrum analyzer! If you don't have that, you can get by with a frequency counter, an RF level meter, and a couple of attenuators. If you don't have that, things get complicated.If you haven't already checked it out, there's a Tek group on groups.io . I found a message thread about a YIG failure.https://groups.io/g/TekScopes/topic/7655774. Looks like the messages are public. It's free to join so since it doesn't look like you're going to get much knowledgable help here, you should join that group.I also see that KE5FX has some 492 service notes athttp://www.ke5fx.com/49x_notes.pdf.Ed

author: memory58
author_rank: Newbie
timestamp: December 10, 2024, 11:50:52 pm
content: Hi,I have already replaced the tantalum capacitor on the YIG... there was indeed a short circuit there...The problem still exists... unfortunately.The boards are a bit older and the through-plating was somehow not done so well by Tek. I'll take a look at the driver board soon. The device is old but complicated....