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Thread: ICOM -725 - fault after storage

  1. #1

    Default ICOM -725 - fault after storage

    Hi, Recently powered up my trusty (it was) IC-725 after it has been in storage, at room temp. in my indoor shack, now I find that it is not functioning within the limits of the bands of Region One - Europe, CIS & Africa. After performing a full test (on dummy load)I see that it not functioning to either Region 2 or 3 either but transmitting over a broader range than the ham bands. My first thought was that the diode D5 was probably open circuit - this I recall was the mod known as the 'MARS mod' which has been around awhile. My rig has never been modified - I bought it new to UK spec. However D5 is perfect, tested in situ it shows a typical forward resistance of 435 ohm with a suitably high reverse. I know that manufacturers often used a diode matrix to determine the market destination of equipment and wonder if that is the case with the IC-725 or are the band settings pre-determined in the microprocessor. I note that there are three other diodes associated with the microprocessor and three blank spaces where diodes could be fitted. The three diodes all check out okay in situ tests. I have tried the microprocessor reset procedure and that appears to work okay as described in the manual. The fault is not intermittent and the rig operates perfectly in all other respects - mode etc. Icom UK are unable to help. I am puzzled.

    Mike GM0OXS

    Tried to reply to the thread but for some reason my replies are not being posted. 'Brandon asked if it was working out of band - No it works on all bands but to a much broader range (broader than Region 1, 2 or 3) with the exception of 160M which is the normal span.
    Last edited by MikeAlex; Fri 24th Jan 2020 at 09:50. Reason: Replies to thread not appearing

  2. #2


    Do you mean it works out of band, but not in band? That's really odd...

  3. #3


    No Russell - it works on all the bands just a much broader range on each band except 160 m which is correct - all other bands are much wider than all three regions 1, 2 and 3. That is what makes me wonder if the region was either preset in the microprocessor or maybe by another IC. The service manual doesn't explain a lot. The microprocessor process reset procedure works okay so that i think te

  4. #4

    Default ICOM 725 Fault after storage

    It transmits on all the amateur bands (all modes) problem is the bands are much broader than either Region1, 2 or 3 allows. the only band that is okay is 160 m which has the correct 1.8 - 2.0 Mhz span. That's why I wondered about the method used by ICOM to set the Region for wherever the rig was marketed. Thought ICOM UK may have been able to help there but they were unable.

  5. #5

    Default Base Radios ICOM -725 - fault after storage

    I have replied to this thread a couple of times but nothing has been posted. I am using the 'reply to thread' button.

    My previous replies were based on the one reply I received and I responded that all the bands were available but that the span of the bands, with the exception of 160 M, was much broader than either regions 1,2 and 3. This suggested to me that whatever method Icom use to determine the appropriate coverage for each specific region had failed. I was hoping that somebody might be able to enlighten me in order that I can investigate further. Is, for example, the specific region programmed into the microprocessor or is it selected by some other means.

    Icom UK were unable to help but did suggest using it but keeping a close eye on band edges here in the UK.

    Any comments would be appreciated.

    Mike GM0OXS

  6. #6


    Sounds like a mars cap mod was done to the radio at some time. I would take ICOM's advice and just watch your TX frequency if the radio works as is.

  7. #7

    Join Date
    Nov 2019
    Ash Fork, Arizona


    Try not to worry about the missing posts. That same thing happened to me, when I first joined. My first 2 or 3 posts never happened. When you first join the group, your posts have to be vetted by the administrator. If it's OK, he/she should let it post. But apparently, that doesn't work too well.

    At first I read this as "735", rather than "725". I have a IC-735 and thought I could help.

    However, I did look around the internet. I couldn't find anything related to your problem. Except for that D5 modifications, there very little on the IC-725. You might want to check the voltages on that diode to see how they act when you go out of the band edges.

    On my IC-735, the diodes that restricted the radio to the ham bands were already removed when I got the radio. But I never let it bother me. Except for my early days as a Novice, when I was crystal controlled, I never let the radio tell me where I can go. I was always well aware of my band limitations. In the early 80s I spent several years in Germany, operating a DA2EU. That was a big shift, but didn't have any problems staying in the bands.

    Like Icom, I would also suggest using it, but keep an eye on the band edges.
    Martin, K7MEM
    Ash Fork, AZ - 60 miles from the Grand Canyon on Rt-66. Elevation 5,300 ft.

  8. #8

    Default Base Radios ICOM -725 - fault after storage

    Hi Brandon & Martin and thanks for the replies.

    I see my first two replies have now appeared.

    I can confirm that having the radio from new, from a reputable UK dealer it has not had a Mars mod performed.

    All the diodes check out okay in situ although I appreciate that is not necessarily the case under power. There's an awful lot of board connectors to disconnect before i can remove the PLL board to check out diodes by lifting one end.Guess now that is the next step. I'll check out your idea martin and look at the voltages at band edges. I wouldn't have thought that Icom would have programmed the microprocessor per region and I have come across diode matrix selction before but in this case everything is as per the schematic and basic in situ tests seem okay - hence the mystery.

    I had though about using it as a dedicated PSk31 or other digimodes unit as I have a Yaesu 450AT in use at present.


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