Der OM kann sich glücklich schätzen das der Tranceiver in deine professionellen Hände gekommen ist. Für die Vertragswerkstatt ist es ein Armutszeugnis sondergleichen, ich nehme mir heraus das als "Murks in Vollendung" zu bezeichnen. Danke für die viele Arbeit mit diesem Video Peter, ich lehne mich auch gerne zurück und höre einfach nur zu.
Hallo Jörg, immer schön dich hier zu sehen! Ja, ich gebe dir recht, das ist Murks. Der Qualitätsanspruch vieler Werkstätten ist leider nicht besonders hoch...
Excellent video and as always a lovely clear fault finding process. Whoever performed that "repair" should have their soldering iron confiscated, just a disgrace. I'm very pleased the radio found its way to you so it could be worked on by a professional.
I agree the best fault finding videos on you tube by far I have learned so much from peter I could never repay him for all his help. He is truly one of a kind person on earth. I wish I had his wealth of knowledge, He is so a kind heart to share with others too a real blessing to me. I am sure for others too.
What a great repair and tutorial. I just had to subscribe. I wish I could work on SMD components, but my 72 year old eyes won't work with such small components. I did understand as you were explaining the diode problem. Glad you were able to fix the radio. If my 991a ever gives up the ghost, I'd want you to repair it. You did a marvelous job on fixing someone else's mistakes. I cannot believe a factory repair would look that bad on a 991a. W Rusty Lane K9POW in eastern Tennessee
Peter, I think this is the best repair diagnostic explanation I have ever watched. It was very interesting! Your testing logic and reasoning is excellent. Great instruction. Thank you for all your instructional radio repair videos ND5CH
They killed poor FT991A, I'm glad they took it to you to give him a new life, hehehe Big hug and recommendations to the family. Here in Brazil, the one who saves us is Yvo Muniz from Alpha Telecon.
Great video again, I sent my FT-991A to the Yaesu service center in California to repair a non working USB port. They said the circuit board would need to be replaced for around $600 USD. I told them to send it back and I would not use that USB port for that much money. That's $800 CND where I live.
I tried to understand the thinking of this hero, when he used this glue - but i didn´t. But someone, who tries to cure the symptom instead of the root cause is capable of doing every nonsense. Great repair with a very logical approach dr Peter!
Nice troubleshooting video as always. The switching transistor is 160V 1,5A which is nice. Some radios can handle just a few milliamps. It is a shame that an authorized repair shop did such a sloppy « repair ». Thanks for taking the time to describe everything!
That was great. A big cup of coffee and a full screen of radio repair on Sunday morning. My compliments to you. Your tenacity and keen attention to the details are admirable. I always learn things from you. Many thanks. Your work is very much appreciated.
Your methodical diagnosis still amazes me after all these years of following your work. You explain what you do and why you do it perfectly, always rolling back a little between each test to see if the conditions of the test from the previous one are still present, which I think is the correct scientific approach. I think I said this before but it is worth repeating once again; I watch your videos with an action movie type of excitement. I don't know what you charge for these repairs but no matter how much, it is worth every penny of it.
Thank you Peter for another mystery solving of radio problems, the proper way. While the other shop didn't really fix the source of the issue, you did it. You're awesome. 👍
Most of this goes straight over my head, love the process that goes into fault-finding. I know if any of my radios develop a fault, I'll be sending them off to you.
Priceless! And talk about timing! I have been putting off this repair for 2.5 years. Yaesu had advised me to look at Q1145 and D1063 so i was quite confident to start the repair. I decided to first take a look to see if anyone else has completed this repair and i found this video. I indeed have 1.4V coming to the switching transistor before it's 1K base resistor. I have 2.16v on the anode of D1113. I just removed D1113 and now have no more connection to ground on pin 2 out for PA switching (which i need PTT to use for a noise canceller i built). I bought the radio like this without knowing. I'll let Yaesu guy in the UK know also. He was very helpful but didn't see this far into the repair. Time to order a new diode. Thanks so much i don't think i would have made it this far. TRX Lab is always top quality! Glad i found the answer right here! And glad i put this repair off till after this video was created! This really made my day! PS. without D1113 in i see 10 Ohms on the PA pin out to ground during Tx.
Great job Peter! Thanks for the informative and interesting video! You said a good thing - "now let's think!". It's a pity that so few people do this during repairs and not only...
Excellent and instructive video. Many years ago, when at tech for auto engineering my instructor had a catch phrase, "Test not Guess", something that works across the whole engineering and fault finding spectrum!
Peter, Once again it was great watching you work through this complex fault finding process. And not for the first time we see that you clearly must have one of the fasted parts courier in the world. You waited 1 or maybe 2 seconds and your parts were delivered. The crew of Star Trek would be so jealous. Seriously that was an incredibly interesting video to watch. Have a great week.
Great video Peter. Thanks for laying out your thought process and showing all the possibilities! It's easy to get loss in the jungle of the schematics. I have no idea of your career path but you would be a excellent teacher!!. Thanks for doing what you do. 73. KM4YTW
BTW Peter I re watched your video(s) at times because your attention to detail is so fantastic, I enjoy learning your TR reasoning and thought process. Many thanks real great learning video.
Unbelievably excellent work Peter. Your skill is out of this world! Such logical work is so impressive. Small components? I struggle with valve radios. Many thanks. Best wishes Lynton G4XCQ
Watching you track back and test the voltage on the diodes was really helpful. It didn't occur to me to consider voltage drop across the resistors along the way, and how that might help you identify which was the culprit. Nicely done!
Great job, Peter. This detective work is what makes it worth it. And we all can say: "thank you dear (insert the technician name) for not destroying the board in the repair attempt"
Dear Peter, excellent repair-video, as always! Hats up to the master ! Wonderfull video, and so excellent handeled and narrated, ... ! Now I now, when struggeling with my 'newer' Yaesu-radios, what I should do, ... ! (Have here a FT-991 without the 'A', and man other, ... !) First, connecting you for an apointment ! - That's a woderfull repair, of a wonderfull radio ! - 73 de Markus - db9pz (JN39fq - 5km/3miles east of LX)
Love your posts. Thank You. Very helpful and the information is sensibly delivered in an otherwise very difficult technical environment . Always an inspiration. Thanks ! 👍
That was a very "naughty" repair, if it was done by a Yaesu Authorised Repairer. Both mis-diagnosis AND very poor execution. I HATE those RF/PIN diode filter switching circuits with a vengeance! The Yaesu FT757 was famous for leaky diodes in its RF board. I once got so fed up chasing a switching fault that I adopted the "scatter gun" approach. I simply replaced EVERY diode on the board! They were through hole types in those days, very cheap switching diodes (not PIN) and easy to change once the board was out. It worked!
Scary to see an authorized repair center produced such a botch / symptom fix... 😬 And why ffs the glue?! (Ok they could have potted it in black epoxy to hide the shame as well.)
Good video. Older Yaesu 757 are good for leaking diodes. Those are through hole though. I think reason for the adapter is just easiest way to get a plug that fits the radio and adapt it to the RCA plugs of the amp to get your PTT and ALC in/out.
Well done, Peter! Nice description of problem and solution. First time "repair" attempt was..mehh. Ich hoffe, es geht Dir gut! Gruß nach HE! 73 de Olaf
Hi Peter, Great detective work to find the real cause of failure. Wonder why they applied that adhesive during the sloppy warranty repair. Stay safe. 73 WJ3U
Hi Peter. Your videos are superb! So much detail and description of your thought process, and all in a language not your own. I speak German pretty well and have tried producing some content in German, which I found to be very challenging. Great respect and thanks to you!!
Superb fault finding skills and explanation Peter as always. Happy new year. I suspect the service tech at the Yeasu service faculty would not and did not the patience or time to go in depth. Thank you 😊
Excellent troubleshooting and video. When you measured the "output resistance" of the collector to ground the two numbers you saw were actually differences in VCESAT, not resistance. For low the BJT was in hard hard saturation and the higher reading it was in soft saturation. To measure resistance the DVM outputs a constant current and measures the resulting Voltage. The key to the measurement was that that the high reading had conduction and was not an open. The only know way I know it was VCESAT change was seeing the schematic. I would think that the leaky PIN diode might affect the RF performance by changing filter response or adding noise. If that was happening you cured it with the PIN replacement.
It was interesting to see a kludge of an attempted repair by an "authorized Yaesu tech" by attempting to increase the base switching threshold of the switching transistor by the accessory port. It is extremely rare for a PIN duode to fail into a zener mode like that. PIN diodes are used as RF switches and as you say can become "leaky", or in this case become a voltage source when reverse biased. That couple of hours (probably 3 or more actually) is excellent troubleshooting. How could the Yaesu tech button the radio back and return it to a customer in a non-functioning state? There has to be more of a back story than is evident here.
Superb troubleshotting Peter, thank you for share!. I´ll try to use some of your analisis of the schematics in order to diagnosticate an issue with my 991A. It has a poor reception in VHF with a high S9 level of noise floor... It´s not the antena or the power supply..,. so it has to be something with a filter I supouse, I´d love to ear some advice you could give me!. Thank you again for this great video!
Excilint video. Brought back my fault-finding experiences from way back, before surface mounts, and building amplifiers enc. Also worked on TV repairs. Where do you get the outlays (handbooks) of the radios, for the circuit diagrams?
Another great video Peter! I have to consider, is this a factory error with wrong part installed? An actual zener instead of the pin? How many other of these could have this defect but owner never used an external PA so doesn't know it? Also wonder how the pulled low rx voltage affected the receiver performance. Anyway you brought it back and that's what matters. Looking forward to the next! 73 Jim WB8ZLK
My Yaesu FT-891 also failed due to a faulty RN142. The diode may have had poor ESD tolerance right from the factory (especially since they discontinued the original version and replaced it)
