ICOM 737 Problems

About five years ago or more I bought a used ICOM-737 for less than half the price of a new one. It has worked fine for over four years and I would consider it the best of any transceiver I have ever had the privilege of operating.

About a year ago it began to demonstrate a nasty habit of shifting frequency by about 50 hz or so. It usually happened when I was transmitting. The shift was not serious enough to loose contact. It merely changed the pitch of my voice on SSB and it did not occur all the time. Only on very rare occasions. At first. Recently it has become more and more frequent.

Then, the other day, it began to have trouble with 160, 80, and 40 meters. It just quit working on those three bands. It still worked on 20 meters and up but the lower three bands were dead. No signals, just noise. The condition went away when the radio was powered down and left overnight. The next morning all bands worked as they should for about fifteen minutes, then the lower three bands would fade off into never never land.

I was convinced that it was a power level problem. The 8 volt regulator was a little low running at 7.25 volts. Or so I thought. Turns out that my voltmeter was off but before I discovered that, I replaced the regulator with a new LM7808. A standard LM7808.
The regulator that ICOM used had the mounting tab insulated. The standard LM7808 had an uninsulated mounting tab. No problem. Tab goes to ground anyway, so I just mounted the new regulator with the uninsulated tab to ground. When power was applied the display remained dark. I re-installed the old regulator, powered up and everything returned to normal. I still had the problem of loosing the lower three bands but at least the display was lit and everything seemed to be working on the bands that were still active.

That is when I decided to see if there were any service notes on ICOM on the internet. Yup, sure were. Most had to do with frequency instability caused by defective plastic trimmer capacitors. The notes recommended they be replace with ceramic trimmer capacitors.

I have not done that yet but I am sure that when I do, the problems will be solved. The parts involved are primarily C294 and C205.

I vaguely recall that the ICOM-735 suffered similar problems which were also caused by plastic trimmer capacitors. My guess is that the difference in price between plastic trimmers and ceramic trimmers might be as much a 5 cents, maybe. You would think that the manufacturer would have learned a lesson about trimmer capacitors from the problems with the 735 model, but noooooo… they needed the those 5 cents far worse than they needed satisfied customers. Well, they better find some part that gives them more than just a 5 cent boost in profit because I am not buying anymore ICOM junk.

I figure if they cannot do the right thing and build in the quality that I deserve in an expensive radio, then I don’t need to do business with them anymore. Besides, I don’t want to find out the hard way the trimmer capacitors were not the only parts they cheaped out on.

By the way if you have one of those trashy ICOM transceivers, I can replace the faulty trimmers for you for a flat fee of $100 plus shipping (both ways, of course).

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12 Comments on “ICOM 737 Problems”

  1. Frank Says:

    I just could not wait until I got replacement trimmers. I took the amplifier unit off for the umpteenth time and tweaked the trimmers. This is the capacitors labeled C-205, C-35, C-46, C-59, and C-70. All of these trimmers were stuck pretty good. Like they have been at one setting for a dozen years or so. I rocked the adjustment back and forth just until they no longer offered much resistance.

    Then I put the amplifier unit back in place, hooked up all the wires and powered up. The radio appears to work now. On all bands. Including the three that were unusable. The tweaking did not seem to throw the alignment off either. At least I could not tell that there was a difference before and after the tweaking.

    The service manual goes through a detailed procedure to align these trimmers. Main problem is how to do that with the amplifier unit removed. The alignment is done with the radio powered up. It powers up through the power connector which is mounted on the back of the amplifier unit. The amplifier unit has wires and cables connecting in front and in back. Makes you wonder how to get to the adjustments because they are under the amplifier unit.

    Well, it is working now. Hopefully it will still be working tomorrow and the day after that. If that is the case, I probably will forget about fooling with it for a while and start using it again.

  2. Frank Says:

    The 737 worked fine for about 48 hours. This morning we are back to the lower three bands being dead to RX and TX.

    Need to replaced those trimmers after all. Also, looks like some work has already been done. There are solder splotches on all four corners of the lid shield. The solder is not done very well either.

    So, need to order the trimmers. A check on the parts available here indicates that there are not enough of the right types and sizes.

  3. Frank Says:

    Got some trimmers ordered. Sprague-Goodman ceramics. Two flavors. Ten each flavor. Ordered from Mouser. 659-GKG20015 is a 5-20pf coded red. 659-GKG30015 is a 6.5-30pf coded green. Comming by FedEx ground. Shipping will probably be around 5 bucks. Parts are only 24 cents each for a parts cost of another 5 bucks.

    Mouser does not have a minimum order and some super good prices.

  4. Frank Says:

    Looks like about three weeks and still no joy. Having the maintenance manual does not help. I took out all the screws holding the troubled circuit board to the radio frame and it still will not come out.

    Been thinking about what to do now. Finally just tried to very gently force the board off and it came unglued. No, unglued in this case is a good thing. Sucker was held to the frame with a large blog of shoe goo. It will go back the same way.

    The underside of the board is covered with soldered on shields. That and the multitude of delicate little wires running to delicate little connectors has me convinced there has got to be someone out there making better equipment. Why, my Korean made VCR is put together better than this thing.

    Finally figured out how to install the new caps. I am assuming that the old caps are set close to optimum. So I will remove them, one cap at a time and use the capacitance checker to measure their value. Then I will set the new, ceramic replacement caps to the same value and install them. One at a time.

    Then button up and hope for the best.

  5. Frank Says:

    turns out it is not glue. It is wax. It melts as heat is applied to the shields to remove them to obtain access for the repair.

    Apparently this is a very vibration sensitive part of the transceiver, but then we already knew that.

  6. g3vbv Says:

    I presume the capacitor replacements fixed the problem. I’m having similar problems on my IC-737 and I have the replacement capacitors, just that I haven’t yet got around to replacing them so far. Hope to tackle that job some time in the next couple of weeks.
    Nice description, stumbled on it after a few weeks of searching, just needed the right keywords in google — “Icom 737 problems” found it.

  7. admin Says:

    I still do not know if the ceramic capacitors will fix the problem. At present I am using an old Kenwood TS-120 and have been for the better part of a year it seems.

    Maybe this week I will finally get the caps installed.
    The problem is that I do not have the equipment I need to align this thing. I was thinking I could measure the value of the old caps and adjust the new ones to match but I have been chicken to do so. \

    Maybe I will just put the rig back together as is (without replacing the caps) just to see if it still works. Who knows, maybe the repair fairies have fixed the problem for me.

  8. g3vbv Says:

    Thanks, I won’t be able to get around to doing anything for the next 2 weeks. When I do, I shall note each as I replace them. If problems arise, I will be able to put them back in their proper places. It’s a pity it’s laid out so it’s not really possible to try one at a time.
    My guess is they have a special setup to allow factory alignment.

  9. g3vbv Says:

    Well, I did the dirty deed replacing the trimmer capacitors, measuring and replacing with the same values. No difference on 40m, may be even worse, but all other bands now OK.
    I shall have to run the rig for a bit longer to verify it’s definitely fixed. Other than on 40m , all the dead spots on other bands have disappeared.

    Not an easy rig to mod around that area. Soldering seems to have been done with an industrial arc welder. A few differences between the service manual and the actual rig when it comes to removing the PA unit, but once the PA screws are removed and the unit lifted slightly, it’s obvious. e.g:- that I can remember, it says J6 instead J8 is the one that needs to be unplugged from the main unit.

  10. g3vbv Says:

    Got a feeling I made a mistake with 40m, it’s completely dead now. All other bands are fine 3+ days on.

  11. admin Says:

    Congradulations!!! I believe you finally got it fixed. If I wore a hat it would be off for you.

    I am a little embarassed that my 737 is still laying on the repair bench. Your degree of success inspires me to pick up where I left off on the thing. It is sort of nice to have other equipment to use but that is not a good excuse to leave the main rig laying around broken.

    I have no idea as to why the problems with 40 meters. I will keep it in mind as I work on my radio and let you know if I have any ideas as to what to do with 40 meters. My radio still worked on 40. It had problems on 80 meters down. Still worked on the higher frequency bands.

    Thanks for letting me know of the progress you made and your success.

  12. g3vbv Says:

    40m was dead 7.0 – 7.1 and at other times 7.0 -7.08, now it’s dead over the whole 40m band, OK 6.999 and below. My problem was seen on other bands, e.g sometimes on 20m it would stop working below about 14.180, on 17m anywhere from the whole band to below 18.120. Results on all bands varied. I suspect the 40m problem now is wrong capacitance value which means I’ll have to take that screening off again and check C35.


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