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Weak TX on Lincoln HR2510

Discussion in 'CB and Export Equipment and Accessories' started by cerapcic, Jul 23, 2010.

  1. cerapcic

    cerapcic Member

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    Hi to all.
    I searched all day for answer and nothing.
    I have President Lincoln radio that has had blown output and driver transistor along with copper traces and one bias resistor. I replaced driver 2sc2166 and final 2sc1945 from Eleflow technologies but output is now very weak and RX is working nice.
    After hours of thinkering and soldering I could not find solution. So if anybody has any idea please let me know.



    How i troubleshoot it:
    1.Turned radio on an measured output and it was very weak (around 3mW)

    2.Started measuring DC voltages along chain of output transistors and everything is according to specs.

    3.Started measuring AC voltages on bases and collectors on chain of transistors after IC106 and this is where becomes very strange.
    Output of IC106(PIN 9) is around 640mV rms
    Q134 base(83mV), emitter(90mV)
    Q124 base(79mV), collector(340mV)
    Q133 base(40mV), collector(170mV)
    Q132 base(20mV), collector(150mV)

    Output on antenna with connected dummy load is 375mV

    (Notice that after each coupling between transistors lot of signal is lost)

    4. Started to inspect inductors,chokes and capacitors everything is fine(even removed glue)

    5. Changed all el. capacitors in TX output section and ceramic that are in RF path

    6. started to get very frustrated...:)

    Nothing is changed. Everything is the same as it was when i replaced burned components.

    I know there are some real gurus here so I would appreciate any help.

    Regards
    Marjan
     
    #1
  2. Quiksilver

    Quiksilver Active Member

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    Rogerbird1 is the Lincoln/2510 man. PM him, or hopefully, he'll chime in...
     
    #2
  3. mechanic

    mechanic Active Member

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    Did you replace the pre driver? Check for burned traces on the SWR board, bad or cold solder joints on the inductors. There are usually two ceramic caps on the underside ( speaker hole) of the chassis, these could be bad or shorted. Check for proper voltage on the B+ rails supplying the finals.
    I'll think of more!

    73 mechanic

    I'm apathetic, and I don't care! :unsure:
     
    #3
  4. Robalo

    Robalo Active Member

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    #4
    Last edited: Aug 6, 2010
  5. Rogerbird1

    Rogerbird1 Active Member

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    Final

    The Output Final is incorrect, the Original output is a MRF477 and can be replaced with a MRF497 - Those are the pin for pin replacement. The transmitter is designed around these finals. I have found no other fully suitable final. The Bias and tuning is best with these.

    I have used a MFR455 - But it is a different case style and will only give minimum output with out some serious drive reconfiguration. (only about 10 to 12w)

    You should be able to get a MRF497 from RF Parts for about $30.

    Roger
     
    #5
  6. cerapcic

    cerapcic Member

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    Thank you all for reply.
    Mechanic: I replaced the pre driver (manufacturer was PMC) but as I recently discovered it was fake 2sc2166 so i ordered original Mitsubishi from e-bay so I hope it will cure the problem.
    Rogerbird1: I replaced MRF477 with 2sc1945 as this video shows: YouTube - ‪PRESIDENT LINCOLN - MRF477 CHEAP SUBSTITUTE OUTPUT TRANSISTOR TEST.‬‎

    I will let you now what is going on with the radio as soon as new 2sc2166 comes.

    Regards
    Marjan
     
    #6
  7. cerapcic

    cerapcic Member

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    Hi all again.

    So a have replaced 2sc2166 with genuine Mitsubishi one and now i have 1w output on AM after made all adjustments. Current draw by radio is around 1A from 13.8 supply. Obviously some other component is malfunctioning, and I have changed almost everything(See first post).
    Any suggestions?

    Regards
    Marjan
     
    #7
  8. jazzsinger

    jazzsinger Bullshit Buster

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    have you checked frequency of output? it may be one of your oscillator signals entering the tx mixer is low or missing.a power meter can't measure frequency,and a radio will never give full output if its only amplifying one of the mixer signals as it will be far too far off the tuned circuits in the final stage to give any decent power.
     
    #8
  9. jazzsinger

    jazzsinger Bullshit Buster

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    if your replacing mrf 477 with a 2sc1945 make sure you keep am carrier to 4w max and ssb power to around 12w pep,the 1945 isn't up too fully 100% modulating an am signal with higher drive levels.
     
    #9
  10. Robalo

    Robalo Active Member

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    After spending so many hours on this radio testing and replacing components I found c119, r158, c60, and c79 bad, but before I replaced these parts the radio only transmitted 1 watt. As soon as I replaced these parts everything worked well.

    so that was the mystery on this radio.
     
    #10
  11. mechanic

    mechanic Active Member

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    Excellent!
    Aging parts and damaged parts are sometimes hard to find as they do not show. In the 2510 series, ceramic caps can be a weak link as they are not up to taking the load of handling RF.
    Your "shotgun" approach found the problem and it worked! Kudos!! (y)

    mechanic
     
    #11

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