Saturday, September 12, 2009

ICOM 735 Plastic Trimmer Caps

Hello All,

Well I finished up replacing the plastic trimmer caps in my ICOM 735 (IC-735), in the end after a few trips to the hardware store and Radio Shack I assembled the right collection of tools and was able to remove the old caps and replace with the new ceramic caps.

When I first encountered the problem of the distorted voice I went to eham.net and posted a question to the Elmers post. I discovered that ICOM had used a set of plastic trimmers that were prone to failure. The solution is to replace the plastic trimmer caps with ceramic ones.

I used the following link http://home.windstream.net/ferncity/icom.htm as my overall guidance for replacing and tuning the trimmer caps. Also, the ICOM service bulletin can be found at the following link, The only delta I found from the preceding link and reaching success was abandoning the idea that you could desolder the top of the metal box (containing the PLL trimmers). In lieu of this I purchased a desolder iron from Radio Shack for $10 and removed the entire box from the bottom of the board. This eliminates the need for a "heavy-duty" soldering gun. The desolder iron has a suction device built into it, which allows you to extract the solder directly from the board. The picture on the left is a photo after the trimmers have been replaced, however the large metal box on the bottom left is where the trimmers are housed.

After removing the box from the bottom you will see what is shown in the picture to the left. I took this picture after replacing the old plastic trimmers, however it gives you an idea of what is under the "hood". From what I read in multiple posts the bee's wax is a "stabilizer" for the trimmers and prevents noises caused by motion and movement of the radio in the RX and TX audio. I used my DVM to adjust each trimmer cap to approx. 6.5 Volts as specified by the service manual and previous link provided in the blog. You'll also want to reference the service manual for reassembly.

I purchased my parts directly from Icom and they arrived just a few days later. All in all, once you give up on trying to remove the cover from the top (at least in my case), it turns out to be a fairly straight forward job.

Here are a few more photos of my installation prior to reassembling the radio.

73s
--Chris





1 comment:

  1. Hi Chris I have the same problem with my icom 735
    I was able to remove the metal cover from the top and bottom. I will probably order the new caps but I was wondering how did it work for you, did you have to make any kind of adjustments or anything after replacing them? Thanks for your help!
    73
    Tom

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