Yaesu FT 817 repair - Part 2 : the fix

In Part 2, I flex my newly acquired hot air soldering skills to remove the suspected dead FET in the pre-amp driver section of this Yaesu FT-817, test the old component and validate its death, and install a new FET.
A quick check for operation of the radio and quantifying the RF power output is made with a homebrew RF low power meter and matching RF tap, this concludes the repair of the rig and it can get back on the air.
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[@timprice3287]

Fabulous result! Another fascinating video.

[@queuerious]

Thank you! Cheers!

[@ukrainehamradio]

I never solder without removing the board from the device. It is very dangerous. The easiest way to desolder a part that is soldered with lead-free solder is to add a little regular solder and then desolder a part. Congratulations on the successful repair!

[@queuerious]

@ukrainehamradio, yes, I did debate to remove the board first, but as the FET was “right there” at the edge and seemed accessible, I did it in situ. Thanks for the tip about ‘presoldering’ to remove soldered items, as adding lead solder would ease the solder mix to aid removal 👍🏻. I am pleased personally to have achieved this repair, as I continue to learn about electronics and repair. I am equally pleased the owner can enjoy his rig (20+ years so far; taken all around the world; keen SOTA activator) once again.

[@BurressEd]

Great video, this might explain why my TX5 is in the tank. I set the radio aside several months back during a move and thought I'd pick it up again. Will certainly be inspecting these FETs and surrounding circuitry. What did you use to replace the 2SK2973? Seems that they're no longer available at DigiKey or Mouser?

[@queuerious]

@BurressEd, I hope the video helps in some small way. I sourced four original FETs (new old stock) on Ebay. There are a lot of smaller independent electronics component sellers that offer genuine NOS items: I am based in the UK, with personal good experience of Cricklewood Electronics and Silicon Ark Electronics, which have had hard to find parts at a fair price. The video is my genuine experience of troubleshooting and effecting a fix. Best of luck in your own adventure!

[@karlfell3768]

Use 425 degrees and 25%. Preload the pads with a little leaded solder if you have an issue. Always better to use higher heat and less working time around surface mount components. Karl

[@queuerious]

@karlfell3768, thanks for the guidance! Glad to see I was not too far off the mark - and a few others have recommended adding leaded solder to pads to help soften/lower the melting point 👍🏻

[@theheathkitshop2424]

After the repair was the +5 V bias correct or was it still 3.8Vish?

[@queuerious]

@theheathkitshop2424, I measured it higher at 4.2V. The TX5 line is perhaps not an ideal 5V in itself, as it only enables bias circuits as required, so perhaps the difference from 5V and my measurement is still sufficient to operate. My investigation through TX5 did resolve the issues (bad pre-amp FET), but I could not resolve that 4.2-5V difference.