An excellent example of how, with high knowledge and the possession of quality measuring and diagnostic equipment, you can achieve excellent results. Thanks for your time and demonstration.

Yikes, I bet those FET's a worth a bundle! Nice that it was just that board. Thumbs up bud!

The experts in RF Amplifiers are very rare and you are one of them, you got a new subscriber

I always appreciated my repair folks, but even more so after following along this diagnosis & repair!

That was better than watching a movie, It was good to watch and learn, thank you TRX Bench.

Fantastic repair way beyond my level of competence and understanding, but you explain things so well I can get my head around most of it. I bet you could make my old FRG 7 really sing! 73’s Lynton

This is amazing. Watching this video and how you methodically progress through troubleshooting the amplifier made me appreciate the work that was involved in its design and construction. I wish I knew enough to be able to build one of these. I don't know where to get a primer on filter networks, and I don't even have faith in my ability to build a power supply of my own design. Someone else's, absolutely!

The suggestion for the changing of the video speed was spot on. Thank you. It actually helps in other ways. Somewhat often people on KZfaq talk a little fast for my old brain, so your speech pattern, at 1.25 help smooth things out, and not be too fast for my comprehension. Your English is fantastic. My ability to sprechen Sie Deutsch ist sehr klein. Maybe 30 words left over from learning a bit from my girlfriend while I lived in the city of Bitburg for a few years. Nice addition to learning some of the language was that her father was a distributor for Bitburger Pils. 40 years of not using it hasn't helped.

Again a very nice instructive video, however I'm a technician but not well-versed in high frequency technic, but your outstanding explanation did me understood everything very well. As I mentioned before with your explanation with the switching power supply, your english is for me as a dutchy, 100% understandable and more clear then a native speaker. Thank you very much!

This guy is next level technician...period prolly the best on entertainment

So thorough and takes a lot of time to put a careful video together as well. Very useful. I'm only just starting to understand so many concepts with amplifiers and information like this is very helpful. Thank you for doing these. All of this to talk to OMs, makes our hobby seem kind of silly really. :-)

You have some nice test equipment. The analyzer to view frequency and the SWR as you switch between the bands gives a cool perspective of health all at once. As always I find watching these videos so interesting, and entertaining, while at the same time trying to learn something more each time I watch one.

Peter, great video. Been playing with high power solid states PA's for years but still learned a lot of the newer techniques. Good job!

An excellent,methodical and complete repair, Peter. Very enjoyable to watch. Thank you. 73.

That harmonic suppression is beautiful at that output power level!

That is one bad to the bone amplifier! Very nice equipment there.

Great video again I really enjoy your videos you are a very good engineer and your commentary is very clear to follow I sit and watch always with interest .Thanks again for posting

I must have missed the AFP re-adjustment that started the whole problem? Thanks Peter for another great video. I appreciate your attention to detail.

After going step by step watching this.... you did everything right. I suspect a roach climbed between that circuit and created a ground fault for a long enough period while the amp was not engaged on. But long enough to create a little mini heating element and the burn occurred. What I don't see in this circuit design is a fuse between the main PSU and this burnt circuit which would have blown at the current a roach would draw. The only flaw in the circuit design was lack of a fuse element after the main PSU to protect the entire system from fire hazard. I will be placing a correct fuse in my own system which is very much the same as this unit but half the output and of course 48 volts. Thank you for posting this video. It was very informative not only for repair study but concept design as well! Good job on the entire video and thank you. If it wasn't a roach then it may have been an arc caused by too much solder on the main (RED) wire that may have melted during or at the end of operation... then while the operator was asleep and the unit still powered... MAGIC SMOKE? He or she wakes up and suddenly the amp will not function.

"Magic Smoke Escaped" I Subscribed and Hit the Bell the second I heard you say that :) . I personally have seen a 1 inch high flame come from one of those SMT ceramic capacitors; those little caps can do a lot of damage. You are an amazing technician and we are all blessed to watch you in action. God Bless You TRX ! 73 Lawrence VA7LTX

Great video once again! I really enjoyed your explanations and walking us through the procedures to test and repair this amplifier. Very well done! 73!

Great diagnosis, it is too easy to rush through a repair, well done for checking the low pass filters. 73

The world needs more people like you! Genius

A good power amplifier will have protection circuitry that monitors forward power, reflected power, input power, output power, output device DC current, output device power dissipation, and of course output device junction temperature. In most cases, the protection circuitry should reduce input drive to properly protect the output devices. The protection circuit should never abruptly cutoff power because, this can generate damaging transients. Instead, it should fold back ouput power like a power supply folds back current when the current limit is exceeded. With the amplifier you are working with in the video, the manufacturer may have set the cutout point at a specific reflected voltage on the directional coupler (which relates to a reflected RF power level instead of an actual VSWR ratio). For best reliability, output power should start folding back at VSWR ratios greater than 1.5:1.

well done Peter that is good testing to check for earth leakage very important were safety is concerned I used to do P.A.T testing Pats stands for Portable Appliance and Testing.

Excellent and informative. Thank you.

Extremely thorough test, really learned a lot and enjoyed! Thanks - Lloyd W9NLA

Another great video Peter! Very well explained. I liked your dummy load... I have a EKD-100 for restoring.73's

I like your DCA55 component tester. It's really useful.

Another great video! I'm going to have to watch it another 6 times for it all to sink in!

Great video Peter, like the safety test performed. Keep them comming. Thanks, Greg

Thank you for this interesting and detailed video. Great troubleshooting.👍

Thank you very much, as always, Peter!!! Great video as always!! That is one impressive amplifier!!

3:49 oh WOW! Thank you for great videos!

Hello Peter for making the nice video, with a thorough checkout of the amplier circuits. I designed some high reliability airborne power amplifers in the past and wanted to add a few recommendations. Since this amplier is for amateur use, the standards I recommend will be somewhat less but, still useful for general guidelines.

Ooo what fun. Looks like maybe an arc over from high SWR caused a thermal runaway. Great video!

Well done! Good repair and good video, as usual! Thanks, Peter! I found myself wondering through most of the video what could have done that kind of damage, but then you found the SWR protection circuit was out of adjustment and the small, seldom used part of my brain that stores useful information realized that a high SWR situation could mean that there were some seriously high RF voltages playing around inside that amp.

Hi Peter. All of your videos are very informative. This one to me really shows your extreme knowledge. I would love to own this amp. I wonder how many the old guy built. Perfect for a transistor amp. I would really love to own this one. The owner should be thankful for you knowledge and to own such a nicely designed amp. Very nice to see it repaired.

Nice work, Peter. Thanks for sharing the repair with us.

Those FETs are huge!

Good explanation of troubleshooting. Thanks for sharing your work. Impressive!

SWR protection circuit was out of adjustment, great job and 73! YO5CAT

Peter, nice one again.Big thumbs up.Well that kind of pots are really bad, I've lot's of problems with them, since that I always use Bourns pots one critical circuits.The fault on the pot could be related to heat that it get's from the RF board, and with time it's gone deteriorate till complete failure.Again good job.

Very concise and very detailed. A terrific video !!!!!!!!!!!!

I always like to keep an eye on you my friend to see what you are up to :) Another great job Peter. Cheers John

Great explanations and good job on the troubleshooting.

Really a Nice video again. Thank you and best regards Peter

Wonderful amp quality

Another interesting video viewed, great job as usual Peter.

You do great work Sir enjoy viewing your videos and learn a few things too. Thanks for sharing.

Very thorough testing very impressive Peter, as usual 73's VK6NJP

Hello Peter!!!...Very nice work, I really enjoy watching your videos!!!

Absolutely wonderful, entertaining and delightful. Glad to be a subscriber.

Another great lesson, thanks Peter. 73s de IW0HEX Pasquale

Enjoy your videos and this one was no exception. I read through the Q&As of others and now have no questions. Good job 73 Leo K1ZEK

This is spectacular!👍😃

Very enjoyable video (still watching it). The SWR detection circuitry is likely between the LPF and the antenna connector. In that location it is unable to protect the FET's in the event of a LPF failure. I have a pair of those FETs for sale should you want a spare. Cheers and 73 - Steve KG4LJB.

Probably Scenario might have been: SMD multi-layer ceramic condensor dying for micro cracks by heat or maybe even from excessive voltage (maybe by VSWR misalignment?) and then being burned off in a few seconds at that rates could lead to excessive oscillation of your Amplifier. That would then lead to massive over voltages which then are sparking over and burning the massive hole into your PCB. Don't you think?

thanks trx bench i always learn from your videos keep up the good work

Thanks for these vodeos Peter lots of good info here.

One hell of a way to keep the shack warm. 73

Great video and some awesome test equipment. I thoroughly enjoyed that very well explained test procedure. I could be wrong but I don't think you reset the Pot to trigger the Thyristor for the AFP LED after turning it fully clockwise.

Excellent video as usual. This channel recommended by Mr. Carlson's Lab.

Very impressive work.

I think the guy who ran the amp lost his antenna and threw the match out of the final stage of the transmitter's load network to the antenna and it fried the final stage of the transformer PI circuit when it got out of tune when the antenna went up in smoke. So we found that the swr protection section didn't work properly to cut power off to the output section of the power to the finals due to a bad pot trimmer. But what caused the high SWR to begin with the operator most likely. Not selecting the right band for operating of the band of output of the radio.

Great repair. All that power output would make me real nervous though.

you could scroll around the 12M band to see where exactly that filter is tuned and then possibly re-tune it.

This is why i prefer Valves to High power transistors, For instance The cost of a GS-35 valve is a fraction of the cost of a high power transistor and a lot more forgiving...... Great video , But Ide take a high power valve over a transistor anyday :-)

thumbs up man, i want one of those 10 kw tube amplifiers for broadcasting ;)

Very nice video Peter. That is quite an interesting amp there. Almost looks homebrew, I guess it was homebrew in more than quantity 1?? Good that you could order a new board. I was thinking you would have to make your own! This kind of amp makes me a little nervous with so much power you can really do damage easily to very expensive parts. Vacuum tube amps are much more tolerant of abuse compared to MOSFETS!

It looks like one of the caps on the output transformer board shorted and started arcing, burning a hole in the PCB. Good fix and testing. I am concerned about the pots on the SWR monitoring bd. It's a critical circuit and it appears that those cheap trim pots didn't age well and their contacts oxidized and the value was no longer accurate until you moved the contact. I'd replace those trimmers with much higher quality ones in order to protect those very expensive output devices.

1206 and bigger capacitors were often short-circuit in my hobby devices - i suppose, it was because I don`t have an infrared soldering station. 4:14.

EXCELLENT !!!

Nice video! I really would like to take a look inside that 1200W RFT dummy load. Thanks, 73.

Very much enjoyed your video thank you regards steve

I am watching it at QRQ speed of 1.5x and enjoyed it.

schönes Output Signal.. sehr nice 73

É bonito ver um verdadeiro técnico!!

RFT KAM-1300 does a good job. 😁

Great video thank you Peter!

those mosfets are super tough, good to 50:1 swr at full load.

That's quite a burnout on that PCB!

Rule No.1 don't play with the pots and cans unless you know what you are doing. Sometimes the pots become corroded and no longer give the correct resistance, just turning it a few times can clean it up but sometimes they need changing out.

I kind of skipped through the video . Did he change out that potentiometer on the overcurrent board ? I would have changed them both .... That was a great Video . I'm building a LDmos amp using a Gemini style chip . Actually a BLF188xr .... Only thing I didn't like about this amp I saw was the single choke on the output board , but other than that , This is a well made, clean , amp....

Very good explanations. Networkanalyzer: would be interesting to know what komponents you need for it.

Interesting and informative video Peter. 73 de Malcolm M6MYB

Did you readjust the AFP trip point and make sure that the adjustnent pot wasn't intermittent?

Great video - very instructive. 73 from VK6HIL

Kaboom, at first glance, not being a tech but electrician, I would have guessed that as a lightning strike.

Danke fuer deine video! Sehr gut! Danke schön.

very informative

Hi Peter, Another great repair job done there. I had to see the funny side to that great big hole in the filter bord. It reminded me of a comedy record that was out some years back and a bed sheet gets ripped open by someones feet going through the sheet. Out comes a voice" Who look at that hole". You would have to have heard the record to see the funny side to it. Not funny would have been the cost if the power Mosfets had blown. Any how a good repair job done Peter. 73 de John - G0WXU.

Very detailed analysis of the issues Peter. That was a lot of testing to go through. You really did a good job of explaining that. You thing it may have just been a weak link in the board that caused the failure? Or maybe that tiny capacitor shorted?Thanks for the great video my friend.

Master Repair. All case are tested.

Dear friend forgive the daring to write to him on his channel but I would like your opinion technique of the problem of my Yaesu FT-450. Here I explain what happens with my Yaesu FT-450. A few days ago I made the mistake of trying a radio from a friend of mine when my FT-450 was on receiving, they had two different antennas but the separation between the antennas on the roof are 3 meters. When I was testing the radio in transmission I felt a burning smell from my friend and I realized that it was coming from my radio, at the moment I turned it off and when I turned it back on it had changed many things like: - TRANSMIT BUT DOES NOT GIVE ANY OUT POWER IN (AM) MODE ON ANY BAND. - THE SYSTEM (ALC) DOESN'T WORK, NEVER MARK ANYTHING ON THE DISPLAY, BEFORE IT WORKED VERY GOOD. - ESPECIALLY IN 6M (50MHZ) BEFORE HAD 100 WATT, NOW ONLY HAS 10WATT AND WHEN CW OR SSB TRANSFER FEELS MY VOICE OR NOISE IN THE RADIO HORN. - THE INTERNAL RADIO TUNER ANTENNA DOES NOT ADJUST IN SOME BANDS AND HIGH SWR WITH GHOST ANTENNA DUMMY 50OHM ADJUST 1: 1 ALMOST ALL BANDS, I REMOVED THE RADIO TUNER ANTENNA AND CONTINUES WITH THE SAME PROBLEM, THE PROBLEM IS NOT THE INT-TUNER OF THE FT-450. - BEFORE ALMOST ALL BANDS DRAWN 100 WATT CW AND ALMOST 90 WATT SSB. NOW HIM RESULT WITH LOAD DUMMY 50OHM PER BAND IS: 160m ... fm .... 100 watt cw .... 100 watt am .... no carrier no power fonia and digital .. 100 watt ----------------------------- 80m ... fm .... 100 watt cw .... 100 watt am .... no carrier no power fonia and dgital .. 100 watt ----------------------- 40m .... fm .... 70 watt cw .... 70 watt am .... no carrier no power fonia and digital ..40 watt ----------------------- 30m ....... fm .... 70 watt cw .... 70 watt am .... no carrier no power ----------------------- 20m ....... fm .... 70 watt cw .... 70 watt am .... no carrier no power fonia and digital .. 40 watt ----------------------- 17m ....... fm .... 50 watt cw .... 50 watt am .... no carrier no power fonia and digital .. 30 watt ------------------------ 15 m ........ fm .... 80 watt cw .... 80 watt am .... no carrier no power fonia and digital .. 80 watt ------------------------- 12m ......... fm .... 80 watt cw .... 80 watt am .... no carrier no power fonia and digital .. 50 watt When I transmit on the phone you can hear it on the radio horn ------------------------- 10m ......... fm .... 50 watt cw .... 50 watt am .... 10watt fonia and digital .. 50 watt --------------------------- 6m ......... fm .... 20 watt cw .... 20 watt am .... 20 watt fonia and digital .. 20 watt, When I transmit in fonia it is heard in the radio horn. He also seems to be crazy, he makes noise and he seems to have serious problems. I RESET HOME OF THE RADIO AND CONTINUE WITH THE SAME PROBLEM, THE PARAMETERS THE HIDDEN MENU IS CORRECT, THE RECEPTION IS CONSIDERED GOOD IN ALL THE BANDS AND MODES. I CHECK THE BOARDS OR BOARDS AND ALL ARE IN GOOD PHYSICAL CONDITION, NONE COMPONENT SEEMS TO BE BURNED. BEFORE MAKING THE ERROR MY RADIO WAS WORKING NO PROBLEM WITH 100 WATT IN ALL THE BANDS AND THE AUT INT ALSO WORKED NO PROBLEM. I HOPE THAT WITH THESE DATA YOU CAN GIVE ME AN IDEA OR OPINION OF WHAT PROBLEM THE TEAM HAS THOUSAND THANKS IN ADVANCE. note :Now I have realized that when I press the ATT or IPO key that is only for reception it falls even more the power in all the bands, in addition I tested it in reception 6m 50mhz and it has problems also at the reception . BEST 73.- EDUARDO CO8LY

Enjoy you videos Peter. Would you consider a video on the Rhode & Schwarz CMT setup and use? Thank you!

Peter, Another nice video. Two thumbs up. :-) WB3BJU

hallo peter, ich habe jetzt einen eintrap in meinem besitz. Haben Sie vielleicht weitere Informationen zu dieser Endstufe? Ich würde gerne wissen, wie hoch die maximale Leistungsaufnahme ist. und ist es gegen zu viel eingang und hohes swr geschützt. bvd Stefan PD5S

Very thorough trouble shooting. Congrats on a fine job. Wa2gzw

Very nice video. 73. AB2ES/7 in Oregon USA