ICOM IC-775 DSP Fans Not Working

Discussion in 'Radio Circuits, Repair & Performance' started by K7QHU, Sep 23, 2019.

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  1. K7QHU

    K7QHU XML Subscriber QRZ Page

    Hello Group!

    The fans on my IC-775 DSP are not working. The maintenance manual for the radio does not mention the fans and on the schematic I can not determine if there is a common part (relay, thermal control, etc.) that controls the fans on/off operation. Since it is unlikely that all three fans (power supply, PA unit and tuner unit) would fail at once, I am thinking there may be a common element to the failure.

    Has anyone else seen this problem and resolved it?

    Thanks in advance for any suggestions/solutions.

    Steve K7QHU
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    I do not know for that radio exactly.

    ICOM is good about having fuses to protect the radio. Many are surface mount.

    Does everything else work normally ? A dead regulator may be something to test for.

    Good Luck.
  3. K7QHU

    K7QHU XML Subscriber QRZ Page

    Thanks for your reply. Everything else on the radio is working great. I will re-check the schematic for fuse locations.

  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    Have you done a radio reset ?

    The CPU may control the fans.
  5. K7QHU

    K7QHU XML Subscriber QRZ Page

    I had not thought of doing a reset. I just tried it and then let the radio run for a while... The cooling fans still remain off. In the service manual for the radio, the block diagram shows a transistor "Q20" marked as "Fan Control". However I cannot locate this on the schematic :(. Thanks for the reset suggestion.
  6. NU4Y

    NU4Y Ham Member QRZ Page

    I have not worked on a 775 and I don't know where Q20 is. BUT
    The PA fan is controlled by Q5,Q7, Q8 and Q9 on the PA PCB.

    They way I see it anytime your in TX, Q8 turns on, turning Q5 on and Fan MF1 should run. Then again what do I know.
    KA9JLM likes this.
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    Do you have a web link to the schematic you are using ?

    I would like to have a Look See.

    Good Luck.
  8. M6AGL

    M6AGL Ham Member QRZ Page

    Check you have good earth connections for all 3 before delving deeper. They all need an earth and that is common to all 3.

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