How to test a crystal in circuit with oscilloscope Vintage Hammarlund HQ-129X shortwave receiver

Here is a nitchy Tech Tip for you. I had an old HQ-129X receiver arrive with inop Crystal selectivity. Normally due to the value of these receivers, most do not pursue a pricy repair. This turned out as a bad connection on the crystal. Fairly easy to repair and inexpensive. So, I saw this as an opportunity to demonstrate a quick crystal testing method. I do not perform this often, but when necessary it is a easy setup. If you look up this subject on the web, most say you must remove the crystal, not true, it can be verified in circuit.

[kateristrobel]

Oh my husband will be a happy camper when he come back from work. Thank you Terry.

[preiter]

Very exciting tip Terry! I'll see myself out...

[rciancia]

You've made something that seemed to be difficult to fix really easy. Great job as usual Terry !!!!

[hestheMaster]

Intro tune is like from 1970. Gimme Dat Ding by the Pipkins. Yeah, I'm old! Good test procedure on a crystal Terry. If I ever try to go into crystal transmitter
or receiver repair, it is something important to know. .

[vinylbeast]

Can you recommend a course/somewhere to learn this stuff? Your vids are great, I am looking into becoming a bench tech of sorts. I like working on my own stuff, I have built some guitar pedals from kits, I take apart old vcrs and practice my soldering/desoldering skills on the boards. I am looking though for somewhere good to learn the basics of electronics tho... I have a sansui aug99-x that sat in a closet, worked perfectly. then was packaged up and moved across country. went to plug it in and it blew fuses immediately upon turning on. I am trying to build up the courage to open her up and look over the bottom of board like in your 77x video.

[sincerelyyours]

Nice tip. I'll remember it when the time comes to restore my Hammarlund HQ-120X. One question to clear up a newbe misconception for me: What's doing the oscillating, the crystal or your signal generator? Or is it both? I thought you applied DC to a crystal to get it to oscillate.

[michaelkesti]

Risking pointing out the obvious... This works because the crystal and the 'scope's input impedance form a voltage divider and the scope displays the divided voltage. At resonance, the crystal's impedance is quite low and just about all of the signal is dropped across the 'scope. Otherwise, the crystal's impedance is quite high and just about all of the signal is dropped across the crystal.

[jordanch]

If you can get your hands on a Sencore FC71 frequency counter it has a built in exciter (up to 20mhz) and crystal test port on the front panel. You can also test them with a grid dip meter but I haven't done that. Is there a way to repair an intermittent crystal, the large box type with the crystal between two plates? Thanks!

[Spentelectrons]

Terry, please consider uploading to Rumble. There's only a few channels remaining and I'm willing to delete YouTube