Yaesu FT 817 repair - Part 1: diagnosis

A chance to (re)work on a classic Yaesu FT-817 5W all mode HF/VHF/UHF amateur radio transceiver. I had replaced the finals board - an almost disposable board, and the Achilles Heel of this model - way back in 2021 when it stopped transmitting for the first time in twenty years, according to the owner.
It's back now for a similar symptom, but I think the issue is different this time.
In this Part 1 video, I poke about and develop an hypothesis of the fault that explains the symptoms.
In Part 2: I buy a hot air solder station to do the repair, source parts and have a go! Then we'll see if Part 1 has the right idea of the cause of the fault! In Part 2 also, I share how I measure RF power with a home brew very low power RF meter from Wes Hayward W7ZOI and how I use it in practical situations. Stay tuned and don't forget to like and subscribe...!
Yaesu FT817 Part 2 - the fix, now available here: Yaesu FT817 Repair - Part 2 - the fix
• Yaesu FT 817 repair - ...

[@stevemobile1]

very well presented ..thanks look forward to part 2

[@queuerious]

@stevenmobile1, thank you! Part 2 can now be attempted as I was waiting to obtain a hot air station for the soldering work. Hot Air Soldering and portable HDD repair: Hot Air Soldering and HDD repair kzbin.info/www/bejne/fmO1Y6eHjJl1iKc

[@queuerious]

@stevenmobile1, Part 2 of this video - the fix - is now available kzbin.info/www/bejne/nYSuZp2gq56MZ5o

[@robgooderham7344]

excellent explanation. Thank you for taking the time to explain.

[@queuerious]

@@robgooderham7344 Thank you for watching and your feedback. I made the video initially to record what I was doing, to share with the owner the progress I was making and ultimately morphed into the video presented here. I am not trained in electronics, so this really is just a bloke having a go and actually solving the problem (check out Part 2 for the fix)

[@kruegdr]

Outstanding video! Great explanation of your troubleshooting.

[@queuerious]

@kruegdr, many thanks for your kind words and thanks for watching.

[@queuerious]

@kruegdr, my Part 2 video - the fix - is now available kzbin.info/www/bejne/nYSuZp2gq56MZ5o

[@chrisj0]

A repair video that ends in a cliffhanger, subscribed!

[@queuerious]

@chrisj0, "Will our hero get a decent hot air solder station? will a new FET bring the radio back to life? Stay tuned for the next dramatic installment of Queuerious Guy: Trapped in Electrospace...!"

[@queuerious]

@chrisj0 Part 2 - the fix - is now available kzbin.info/www/bejne/nYSuZp2gq56MZ5o

[@1903A3shooter]

the same FET shorted during battery charging on my early vintage 817, W4GSM

[@prillewitz]

For me with basic understanding of electronics but knowledge of resistance paths I totally understand your way of thinking. Only de soldering can give you the right measurements but that’s not desirable with those small parts. The FET seems to be the suspect.

[@queuerious]

@prillewitz, Yes, the comments I make about the resistance values I measured are observations that support the hypothesis that the FET(s) is/are dead in the pre-driver circuit. The logic is consistent with a bad FET fault. I am saving up to get a hot air solder station soon and to start the repair. I have another small repair that needs this tool too (a dead portable HDD that I need to get working again). I shall post the repair outcome in a few weeks I hope. Thanks for watching!

[@queuerious]

@prillewitz, Part 2 of my video - the fix - is now available kzbin.info/www/bejne/nYSuZp2gq56MZ5o

[@ukrainehamradio]

Great investigation!

[@queuerious]

@ukrainehamradio, Дякую тобі!

[@queuerious]

@ukrainehamradio, Part 2 of the video - the fix - is now available kzbin.info/www/bejne/nYSuZp2gq56MZ5o

[@richardsage3139]

Mine stopped tx&rx on 2m 440 but works fine on hf and 6m anyone know what might have went wrong?

[@queuerious]

@richardsage3139, just looking at the schematics, you will notice that tx and rx on all bands pass through the same filter network section of the rig. If it has stopped working on 2m and 70cm, but works (rx and tx) on HF/50m, then I'd look at the switching relays: on tx, there is relay RL3017 that switches HF&50 / VHF&UHF, and transistor Q3021 that signals to this relay to tx in VHF or UHF - if either failed, it might operate only in one (HF&50) and not VHF/UHF. But I cannot explain rx VHF and rx UHF failures by relays alone, since these bands have different signal paths through low pass filters (VHF) and specific UHF high pass filters.... I do see however, in the block diagram, a diodes D3003, D3005 that control rx/tx of VHF and D3004, D3035, D3006 that control tx/rx on UHF. If a pair has blown, this would kill UHF/VHF in tx and rx, but leave HF/50 working. Get the service manual (google it), look at the Block Diagram (p. 5) and work from there... good luck!

[@carl-gunnarhillefors7612]

SIR! WHERE IS THE PART2 OF ERADICATING A FAULTY FINAL TX STAGE OR [PA BOARD] COULD YOU GIVE THE PART 2 OF THIS REPAIR! I AM CURIOUS!

[@queuerious]

@carl-gunnarhillefors7612, Part 2 is in the works: I need to get paid, get a hot air station, get some practice, do the repair, and test the result… I hope to release Part 2 in the coming few weeks!

[@1903A3shooter]

SAME FET shorted on my early 817 W4GSM

[@queuerious]

Part 2 of this video - the fix - is now available kzbin.info/www/bejne/nYSuZp2gq56MZ5o

[@juniorocicat9573]

It’s a Yaesu what do you expect, should have bought Icom….

[@queuerious]

@juniorocicat9573, 😂