Atlas 110 transmitter rf fading after 2 min of CW

Discussion in 'Radio Circuits, Repair & Performance' started by KD2PK, May 9, 2012.

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  1. KD2PK

    KD2PK Ham Member QRZ Page

    Both the transmitter and receiver work great, but after 2 minutes of CW, the rf output drops to nearly zero. Simply stopping CW for a few seconds, it returns to normal operation.

    I have heard that there is a modification to a protection circuit that fixes this. There is no mention of such a circuit in the owners manual and if there is one, it is not obvious to me on the schematics.

    Can you help ?

    Many Thanx.

    kd2pk.....greg 73
  2. KD8DEY

    KD8DEY Ham Member QRZ Page

    Fading power is usually the sign of something (semi conductor) getting too warm.
    I'd check to make sure everything is properly heat sinked (Mounting & sufficient compound applied)
    condition of any nylon mounting screws etc

    Last edited: May 9, 2012
  3. W9GB

    W9GB Ham Member QRZ Page

    Atlas 110 Line, the Twins. There were two versions (L and H) of the TX 110 --
    based on power output. 110 Line Brochure.pdf

    Photo from WB6VHK Collection

    For your question / issue: Check your DC Power Supply and input. Loss of regulation, in linear DC supplies, can exhibit this type of problem.

    Atlas TX-110 Schematic TX-110 Diagram.pdf

    All About Atlas Radios

    Service Bulletins Reviews
    Last edited: May 9, 2012
  4. KD2PK

    KD2PK Ham Member QRZ Page

    to W9GB

    AWW- COME ON ! The one to solve my problem has my initials ! (GB) mine are GWB..Talk about karma.


    First, I apologize for the late reply. I have not looked at this forum since my post (assumed replies would go to my email.....DUH )

    Anyway, at first, I did consider my power supply, but the voltages were what I thought were "close enought" and even though the lo voltage supply changed only 0.75 volts during the rf drop, I mistakenly dismissed it as normal.

    So today, after seeing your post, I connected my rig to my bench supply instead of using the on-board supply. Result....... I could not get a change in rf, even after 3 minutes of "key-down".

    So now I have to find and adapt a regulator chip since the one from Atlas is out of production. Not really a problem though.

    Thankx again.

  5. W9GB

    W9GB Ham Member QRZ Page

    OK, I am a bit confused. WHAT are you using for the AC to 13.8 VDC power supply (that is failing)
    for this Atlas Radio??

    Is it the Atlas PS-110 matching power supply??

    What is the regulator chip (IC) and Pass Transistor that you are looking for?
    It should not be that difficult to repair !!
  6. KD2PK

    KD2PK Ham Member QRZ Page

    THe power supply I am using one is a small, variable one that I built in an NRI training course (CONAR) on electronics. It had also gone bad, the reg. chip died years ago and is also no longer available, so I replaced it with a new one by adapting it as well. I connected it to the 14V low power input on the back of the RX110 which bypasses the on board supply when was not plugged in..

    The regulator chip is a 78MGT.... rather strange looking package. I think that I might just build a whole new supply with 9V and 14V outputs (1A each) using only the on board transformer.
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