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R-390A Crystal fix

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R-390A Crystal fix Empty R-390A Crystal fix

Post by LarryC Fri May 23, 2008 11:15 pm

Hi Everyone,
While working on a Collins 1955 contract set ( I believe), I had the problem of a few bands being dead. Swapping out the crystals showed that the 9.0 and 11.5 mc crystals were dead.
I looked at the crystals closely and it looked like they were soldered around the base of their covers. I decided to go ahead and open them up and see if it was a bad solder joint or something.
I used a small butane hand torch for this and it worked out great at loosening the base from the cover. the element of one unit was slightly bent to one side and may have been touching the case. I re centered the crystal element and tried it in the radio and it started working normally. Great!!! one down one to go. The second crystal wasn't bent to one side like the other so nothing obviously wrong here. I inserted it in its socket on the radio and it was still dead, so I started moving it back and forth a little and it started back up again. I think maybe where its connected to the crytsal element the wires are crimped on and may be somewhat oxidized. By moving the elements as I did, I may have re established a good connection with the crystal element. I think I may try applying a little de oxit and see what happens long term.
Hopefully this works for you as well, after all you have nothing to lose by trying.

Larry
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Post by Resistance is Futile Wed May 28, 2008 1:25 am

Here's another tidbit I learned while working. and putting two and two together..

You can take a signal generator and hook up a crystal in series with the output lead and it will pass only the frequency of the crystal. So if you have a cheap signal gen that is very broad band which most are, then as you sweep (move) the dial you can inject a very precise signal into your radio.

You could also try the opposite, hook the crystal in parallel with the signal and the return ( or shield cable) and it will pass everything but the crystal frequency.
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Post by LarryC Thu May 29, 2008 4:22 pm

Your using the crystal as a bandpass filter in that application or band reject filter, in both cases a very very narrow band lol Smile
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Post by LarryC Sat May 31, 2008 6:43 pm

Here's a link to the crystal fix section of my website. Enjoy Very Happy

http://home.earthlink.net/~chestnutl/Helptipspage3.html
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