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PLL Unlocked

Discussion in 'General Technical Questions and Answers' started by VO1GXG, Jan 13, 2008.

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  1. VO1GXG

    VO1GXG Ham Member QRZ Page

    My Kenwood TS-450SAT is giving me the warning " UL " Which means PLL Unlocked. What would cause this? everything works fine, the receive screwed up though. if i tune to a local AM station i get no reception , move up a bit and back down again it is cutting in and out, move up some more and back again and its perfectly fine. After a 10 min warm up period the radio is back to normal will no warnings.Is there anything i can do? Is it a expensive repair?
     
  2. KL7AJ

    KL7AJ Ham Member QRZ Page

    How can you say everything works fine if the receive is screwed up?

    Lotsa things can cause a PLL to die.....and if it does, you're dead in the water.

    ERic
     
  3. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    The first thing you need to check is the optical encoder on the dial.  Chips normally fail or they don't so look for bad connections or anything else that could cause intermittent failure.  

    If you need to replace the chip,  I'm willing to bet you can get one if you dig throught the Kenwood forums.  But I have to stress that it is highly unusual for an IC to act intermittently so look at the peripheral circuitry associated with the PLL first.

    Look for diodes, capacitors, resistors and any other peripheral components. Look especially at all solder joints, grounding points, and switch/PC board contacts.
     
  4. AB9LZ

    AB9LZ Ham Member QRZ Page

    I've had problems with intermittent grounding on several of my older Kenwoods. The dissimilar metals between the screws and the circuit boards can cause issues as the years go by, fortunately this is an easy fix by resetting the mounting screws for the boards, and adding star washers if you have them handy.

    Also, the multi pin header connectors seem to be prone to intermittent connection problems with time, re-seat these as well.

    With a little luck your radio will be cured.

    73 m/4
     
  5. VA2GK

    VA2GK Ham Member QRZ Page

    first you have to find which VCO/PLL unlocks, there are usually 4 VCOs for the different parts of the HF band, from 30kHz to 30MHz.
    example:
    VCO1 30kHz to 1.699MHz
    VCO2 1.7MHz to 4.999MHz
    VCO3 5MHz to 15.999MHz
    VCO4 16MHz to 30MHz

    It's numbers out of my head, yours may vary but it should be around that. Check if the problem is present on all four bands, and if it's more obvious at the top end or the bottom end of each band.

    When you have all this done, come back to us.

    Remember, 75% of the troubleshooting can be made with the cover on, just fiddling aroung with the controls to verify its behaviour.
     
  6. VO1GXG

    VO1GXG Ham Member QRZ Page

    The receive is messy from 30khz to 3.5mhz. Everything else is fine. After 2 minutes of powering being applied all is fine.
     
  7. AB8SG

    AB8SG Ham Member QRZ Page

    I don't have a 450, but a lot of Kenwoods PLL unlock when the voltage to the VCO drops below 5 volts or becomes unstable.
    If you have a service manual, it should give basic test points for checking the voltages.
    73
     
  8. VO1GXG

    VO1GXG Ham Member QRZ Page

    Thats a good idea.

    Just checking it i notice the following

    " 4) Unlock signal (PLL unit)
    If each PLL Loop is unlocked , Pins 8 of IC5 and IC6 go low, and the signal passes through the inverter and goes through the digital unit as a high UL signal. the microprocessor puts up ' ......' on the display or outputs a RBK or ABK signal "

    I know for a fact I'm not getting the decimal points, as for the RBK and ABK signal I'm not sure what that is it might be the audio tone I'm getting.I was talking to a friend of mine who said if the PLL was truly unlocked i wouldn't be able to operate the radio. I have had the radio on for 25 mins now and it is running fine, I'm listening to a round table of US hams. could it be the alarm tripping? or the signs of a developing problem?

    Seems way over my head at the moment. I will check voltages, it might be my power supply not giving enough voltage.
     
  9. KB0TT

    KB0TT Premium Subscriber QRZ Page

    I am curious on how this malady pans out ...

    I first thought about voltage instability , yet why does the unit appear to work fine " after warm-up " ?

    Then came the P/S suspicion ... Sumpin' isn't right ..

    Keep us apprised ....


    JB
     
  10. VO1GXG

    VO1GXG Ham Member QRZ Page

    I certainly will sir .


    I am testing the power supply first, So far nothing interesting yet.
     
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