Repairing an Icom IC 751 - Stuck In Transmit Mode and No Frequency Display

Discussion in 'Radio Circuits, Repair & Performance' started by KJ7LYB, Jul 11, 2020.

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  1. KJ7LYB

    KJ7LYB Ham Member QRZ Page

    Hi all,

    So I am attempting to repair my iCom IC 751 after the power supply fuse blew, after replacing the fuse, what is happening is the radio went from not powering on at all to getting stuck in transmit mode and no frequency display.

    See the video on Google Drive for what is going on:

    https://drive.google.com/file/d/1E6OIrouxzKsBvga-TEeeoL5eszbzj2-N/view?usp=sharing

    This is my first time attempting to repair a HAM radio, and after this happened the radio would not power on. Well, the radio does at least power on at all now that's some progress I guess. I was advised to try replacing the RAM Unit in the radio ordered one today and going to put in when it arrives. Having to order the parts on Ebay.

    I am wondering what to try next of replacing the CPU RAM unit does not work?

    Is there a way to test if the motherboard is ok using a multi meter, or a picture of this radios motherbaord here? it is the non A version. Thanks very much.
     

    Attached Files:

  2. VE1IC

    VE1IC Ham Member QRZ Page

    The non “A” version has a RAM board. If the battery is flat or disconnected , the RAM forgets all its programming and renders the radio useless. Check the battery voltage on the RAM board.
    There are 2 ways fixing the RAM problem.
    First one is to replace that RAM board with a non volatile memory board, these can be still had.
    Second is to try reading and writing to the RAM with an eeprom programmer, like TL866ii. There is a guy that makes adapters for it (I bought one). The software that needs to be programmed to the RAM is available on the internet.
    I’ve brought a couple IC-751 back that lost the programming on that RAM card, by changing the battery and reprogramming the RAM.

    no, you need a known good RAM board to start with.
     
  3. KJ7LYB

    KJ7LYB Ham Member QRZ Page

    I bought a new confirmed working RAM board on ebay, Going to put it in when it arrives. How do I check the voltage on the battery? I have a mulitmeter if I can use that. I had heard that could be the case or a circuit died in the radio. Thanks.
     
  4. VE1IC

    VE1IC Ham Member QRZ Page

    Let’s see what happens when you put the ram card in.
     

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