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Understanding my crystal oscillator

  1. Jul 24, 2013 #1
    I have an obsolete, proprietary crystal oscillator. It is a 200MHz, 10 pin, SMT component. The number on the unit is 200N1. I cannot find another C.O. like it in size, number of pins or footprint. What I don't understand is 9 of the pins are grounded. Only one pin is used and it obviously puts out the frequency. How does that work? We have 100s of units we repair with this C.O. in it and they are starting to fail due to age and heat.

    What we would like to do is find some comparable C.O., mount it on a small PCB, which in turn would be mounted to the footprint of the old C.O.

    I am an electro-mechanical engineering technician, not an engineer. Our EE on staff has no clue, either. Any info would be much appreciated!
     
  2. jcsd
  3. Jul 24, 2013 #2

    mfb

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    You get a (working) frequency output without any power source? I doubt that.
     
  4. Jul 24, 2013 #3
    Then tell me how these things have been working for 15+ years? Tell me how I'm reading 200MHz on my frequency counter from that single pin that isn't grounded like the rest?

    If you would, give me your email address. I will send you a picture of the board (w/o crystal) and schematic.
     
  5. Jul 24, 2013 #4
    I just figured this out. New to this forum :-) Here are a couple of pics. One of the PCB crystal area and one of the schematic.
     

    Attached Files:

  6. Jul 24, 2013 #5

    Averagesupernova

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    Are you sure it is 200 Mhz? I have never heard of one run that high even when operating on an overtone.
     
  7. Jul 24, 2013 #6
    A crystal oscillator is a 2 pin device.

    From your schematic, transistor B13 is a connection to Xf, the other being ground,

    B13 has the base connected to ground and the one connecton of the CO connected to the collector and emitter of B13 through a capacitor. So all that does not make sense. You may want to do a retrace.

    Obviously, for a replacement you need to match the frequency. And the power of the oscillator.

    Look up crystal oscillator on the internet. You should be able to find some formulas and description of circuits if your EE is not up to the task.
     
  8. Jul 25, 2013 #7
    That would be Q13, not B13. One thing I saw missing on the schematic was pin 6 of the crystal going to gnd. The Q13 transistor C, B, E is drawn incorrectly, internally, however the actual traces are completely correct. You can verify that 9 of the 10 pins are connected to ground by simply looking at the picture of the board I posted. I know this isn't a typical crystal oscillator. I get how most of these function. This one I don't. I've had other EEs look at this and they just shake their heads. But they know it works somehow, obviously because I can read 200MHz on the freq. counter.
     
  9. Jul 25, 2013 #8
    Okay, so I think I might know what's going on. Who knows about OCXOs? That's what this is and the answer was there all along. I just didn't connect the dots. Someone here may have been able to point that out had I shared the entire schematic but I could not legally (or ethically) do that.

    I suppose my question now would be this: Shouldn't it be possible to replace this OCXO with a VCXO, by removing it from the heating circuit and tapping in a voltage? Or is it much more complicated than that?

    Thanks for the replies.
     
  10. Jul 25, 2013 #9

    davenn

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    we don't really need to see the entire schematic BUT we DO need a real schematic of the area of the circuit concerned and not some hand drawn thing probably so it seems full of mistakes.
    there's obviously problems with your schematic concerning Q13 and its connection to the XO or whatever it is

    what heating circuit ?? there is no obvious heating circuit

    I like others are wary that this is even an active crystal osc. At best it could only be a standalone crystal, since there is no power connection to it
    it still cant be an OXCO still not enough active terminals. there would have to be 3 or 4 active terminals, heater supply, osc supply, output

    AND PLEASE show us a sharp well lit photo of the device!


    cheers
    Dave
     
  11. Jul 26, 2013 #10
    Okay, guys, I appreciate the help, but some of you are kind of rabid! This is the only schematic of this PCB, save the one locked up in Japan by the designer. And as I've said, the only thing not accurate about the schematic is the transistors weren't drawn to show the proper B, C, and E points - and pin 6 of the CO is grounded. Otherwise, it is accurate! You have no idea how many years and how much time I've spent on these units! I've repaired thousands of these, so please cut me some slack. If other EEs haven't been able to figure this out don't automatically assume I'm full of it. No other engineers who've looked at this unit have had a problem with the schematics, either. I'm just asking for help in figuring this stupid thing out.

    The COs have been failing left and right recently so I've been replacing them with COs from scrapped-out units. Now I've run out of spare parts. This CO is obsolete and proprietary so the manufacturer doesn't have any more and won't release any specs other than it's a 200MHz CO. Yes, they said it was a CO. Maybe they told me wrong, but I usually trust the manufacturer. Ultimately, I'm trying to find a way to replace them with something that will work.

    Heating circuit: As I said, I couldn't show the entire schematic, but there most certainly is a heating / cooling circuit that affects 80% of this PCB. As the heater heats up the aluminum plate the board is mounted on the oscillator comes up to the full 200MHz. The board is then regulated by a dual comparator to alternate the heater and fan to maintain the proper temperature. It affects the RF amplifier and it sure seems to affect the oscillator.

    Again, I'm no expert on crystals or oscillators / oscillating circuits. I'm an Electro-Mechanical Engineering Technician, not an EE. From researching OCXOs yesterday, all it would need to drive the 200MHz output is the heater. Maybe the information was wrong. I don't know.

    A picture of the item will have to wait. I'm home today. Thanks.
     
  12. Jul 26, 2013 #11

    davenn

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    its very difficult for any of us to give you valid answers when you cannot give us valid information
    its even more difficult when the small amount of info you are giving us doesnt match with what we are looking at

    you also need to understand that you are not dealing with a bunch of second rate techs.
    I have been building and working on RF circuits for over 30 years and I by no means claim to be an expert
    There are other guru's on here that far outclass my abilities in both RF theory and practice

    but it still boils down to the fact that if you cannot supply us with good and accurate info, then I'm sorry, there's probably not a lot we can do for you

    if you insist on hiding behind secrecy reasons for non-disclosure, then the only choice you have is to take the board back to the design dept in your company and tell them to fix their poor design work

    regards
    Dave
     
    Last edited: Jul 26, 2013
  13. Jul 26, 2013 #12
    Dave, we didn't design this board. There's nowhere to take it back. This was designed in Japan 15 or more years ago - by a different company. Yes, I am under a non-disclosure agreement so I cannot show the entire board or schematic. I'd like to keep our customer and my job.

    What additional information do you seek that I haven't given? I've shown the entire circuit related to the CO and have described the thermal cycle. I attached a picture of the board where the crystal sits - where you can clearly see 9 pins are connected to each other and ground - yet for some reason nobody believes there's only one pin not connected to ground! My original post gave the CO part no. (200N1) but again, it was made specifically for this PCB and is long obsolete. No research is going to give you any more information about this exact CO or PCB. It's obvious this is not a typical oscillation circuit. But it does work - somehow. I think the real reason people are getting a bit testy is because they can't figure it out right away and it frustrates them - just like our EEs. That's not a slam against anyone, but I'm sure I'll get roasted for this observation... ;-)

    I never said anyone on here was second rate and I don't want to be included in that description, either. We all have our different experiences and expertise. Mine is very limited in RF and oscillation. My expertise is Electro-Mechanical repair. I also design and build test equipment. I develop repair programs (such as this unit) where NONE exist anywhere else in the world. These programs have saved our customers millions of dollars. So I'm not second rate and the whole reason I'm on this forum is to pick the brains of first rate engineers! Thanks.
     
  14. Jul 27, 2013 #13

    vk6kro

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    This could be a SAW resonator. SAW means Surface Acoustic Wave so they are not the same as quartz crystals, but they operate at VHF and UHF frequencies which cannot easily be achieved directly with crystals

    These are used in remote garage door and car door openers, usually in the range of 300 to 440 MHz.
    There narrow spectrum allocations for the use of these short range devices and this varies according to the country.

    The device on the board is not the oscillator, by itself, but it controls the frequency of the oscillator.

    Digikey sell many different frequency SAW filters and resonators including some for 200 MHz.

    http://media.digikey.com/pdf/Data Sheets/Panasonic Semiconductors ICs PDFs/EFO-H.pdf

    although the frequency accuracy, in this case, is not very good. They can be up to 250 KHz off frequency.
     
  15. Aug 1, 2013 #14

    NascentOxygen

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    I suspect that there is no way to make use of a small variable C or L to tweak this SAW oscillator's frequency?
     
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