Replacing the Schottky diodes in my FT-847

Some time ago I blogged about Radio improvements and tweaking things to make them better, specifically a number of modifications that I’d had made to my Yaesu FT-847.

I talked in that entry about swapping the cheap switching diodes out for low noise Schottky diodes to reduce the HF noise floor and I said I was going to do it myself.  I really haven’t been able to find the time to do it and I didn’t want to take the risk of damaging my wireless when I’m less than 20% into the QSO365 project.

So today I dropped my radio off at the local radio shop, Coastal Communications and left it there while I went to have some work done on my car.  I did stay around long enough to take some photographs of the work in progress.  The captions will speak for themselves.

FT-847 with the cover off and the board loosened

FT-847 with the cover off and the board loosened

The diodes have all been cut out, the legs are being desoldered

The diodes have all been cut out, the legs are being desoldered

Installing the replacement diodes

The Schottky diodes are being fitted ready for soldering

Most of the new diodes are in place

Some of the new diodes are now in place

The first lot of diodes being soldered in place

The first lot of diodes being soldered in place

All the new diodes are now fitted on the board

All the new diodes are now fitted on the board

At this point I had to leave.

When I returned I was greeted by a reaction of utter amazement.  Not only did Richard replace the diodes for me but he noticed that some of the inductors in that section looked a little dodgy so he replaced them as well.  He’d been a little sceptical as to this modification but he told me that when he first switched the radio on after completing the diode swap that he thought he’d broken it because it was so quiet.  A quick tune around the bands showed him that he was wrong though and that the radio now has a significantly lower noise floor than it had before.  It’s a fantastic modification that I recommend to all FT-847 owners.

These are the diodes to swap and it’s quite clear from the images above how straightforward it is.  They’re not difficult to get to and it only takes an hour or so to do the modification.  I used BAT85 Schottky diodes.

More details about this and other modifications for the FT-847 can be found in the document by Jochen Heilemann, DG2IAQ which you can download here: Modification Sheet YAESU FT-847.

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4 Responses to Replacing the Schottky diodes in my FT-847

  1. Rob M0VFC says:

    Ah, to be in a situation where my radio was the limitation on the noise floor…!

    S5 is as low as it gets on 40m here, and there are significant chunks of the band >S9 noise. Need to go on a DF hunt, but I have proved it’s not from my house at least (by killing all mains)…

  2. Terry Maton says:

    My gosh! You had Isaac Asimov modding your wireless! Gasp!

  3. John Crowell KE5GFJ says:

    Based on this article and others recommending the diode switch I ordered the Schottky low noise diodes and spent all day changing them out. A few of those a difficult to change. After completing the diode mod I put the FT847 beside my other unmodified FT847 and compared them back and forth for several hours on different bands. I hear and see no difference at all after the mod. Both the modified and unmodified FT847s sound the same. i wonder how many people who have done this mod actually had a second FT847 to directly compare it to.

  4. g6nhu says:

    Thanks for the comment, John as it’s quite interesting to read. I’ve read various reports which say that replacing the diodes can make a difference and others that say that it makes no difference whatsoever. In the case of my wireless, I’m confident that there was a big reduction in the noise floor as I’d owned it for quite a while before the mod was done and it was very noticeable. As I commented in the article, Richard actually thought he’d broken the radio when he switched it on after replacing the diodes because the noise had dropped so much.

    Having said that, some months later, Richard bought himself an 847 and did the same modification but like you, he noticed no difference so I think that it’s a bit hit and miss. Some radios benefit from it, others don’t and of course, there’s no way to tell beforehand whether it’s worth doing or not.

    You might find that if you do your unmodified FT-847 that it makes a difference!

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