Thank you Tony for sharing your extensive knowledge with us and always clearly explaining how you go about troubleshooting the various faults you find. Clearly you know your stuff and you are an EXCELLENT teacher, in my humble opinion! God bless you and I look forward to "our" next project, with you at the helm. Stay safe and healthy Tony.
Excellent, thank you Tony. I'm learning much from your patient and methodical approach. Also loved the shout out to Big Clive, it always interests me that CZcamsrs with very different styles but a fundamentally common interest watch each other's channels. The sense of diversity and community is when the internet is at its absolute best, and fortunately this far outweighs the more negative aspects.
Thank you Tony for another informative series of videos. I'm just a rank beginner in this subject and I have to be honest and say that I don't understand 90% of what you are talking about but I find your (lectures) so interesting and I watch every episode. You certainly missed your calling as a teacher because you are very inspiring.
this was an awesome repair series on the kenwppd ..and why im a fan i guess of your channel, i have learned a bunch of things i would not have considered before and have added to my knowledge base.. great perserverance ..many would have either tossed it or scrapped it..you fixed it thats the difference..cheers
Thanks Tony for all your hard work and I think that reciver is blessed to have owners over the years that loved it and tried to keep it alive 🙂. You would have made an excellent medical Dr. I think 😇
very interesting and informative series,it takes a special kind of person with such dedication to bring vintage gear back from its previous state,thanks for sharing brother!
That was one heck of a job to complete. I own a 35 year old Kenwood component style system and it's still working like new as far as I can tell. Some rotary controls have a little dust in them but not bad. This one has a digital FM tuner. I've owned this system since it was brand new in 1985. Anyway, good job on that Kenwood receiver!
Wow, what an epic production that receiver was. But in the end, it turned out nice, I love the look it has with the dial lights and the indicators for FM Mono/Stereo and the functions selected.
Well congratulations on yet another great restoration project completed. Good to hear that some of the comments actually was correct and helpful for you. No doubt that you would have made it alone also considering your knowledge in this field. It's really a challenge without a proper service manual or correct schematics. Well done.
Tony, you are quite the teacher in my eyes...I have learned much in this adventure and it is safe to say, I will without hesitation, stay away from the Kenwood TK-80U if one ever crosses my path...😁
You deserve a holiday after this one, either that or a spell in the funny farm : ) Most of us would have given up ages ago and chucked the bugger in the bin. Hats off to you, amp fixer to the gods....DA.
Tony, I’ll have to nickname you Calypso, (after the John Denver song) .. “Aye Calypso, the places you’ve been to, the things that you taught us, the stories you tell” ...
It looks so much like my kw-55 I think they took the same faceplate, control and knobs. Except the kw-55 is a all tube unit with 17w channel EL84 pp. It sounds good but could be better. The fm receiver is very sensitive.
@xraytonyb So 30-40 years later, As of today, We replaces Electrolytic Capacitors And known bad Transistors, Tony oh know! Did you discover that in the next ten years we will also have to add to Resistors & Germanium Diode???? I have a Pioneer RG-02 re-Build Kit (caps,trans) and still has problems, After this video I will replace the 4-germanium diodes, I hope it fixes it.(Only thing left are Diodes,ceramic,see through capacitors and resistors Lol)
VR3 looks to be some kind of blend control. You can reduce the noise by mono-ing the high frequencies. (Most of the noise is hiss in the L-R signal, resulting in hiss that is out of phase in each channel.) But too aggressive and you lose separation. C26 should probably be a non-polar cap.
Hi Tony, this stands as a tribute to your exemplary knowledge and patience! I fail to see how you could have conveyed so much valuable information in a shorter video - perhaps some folks don't want information, just simple answers?
I had no problem with the length. I'm glad for the breaks and, with a little patience, when you consider the incredible enjoyment with your audience, isn't it really worth it? I would go through it again! Thanks to all!
Tony, Unless I missed it, you never told us what the issue was in the buffer amplifier after going through it and reverse engineering it. You said you flipped two of the capacitors so the polarity mached the schematic, and that the two stages were directly coupled. But I didnt catch what exactly was causing the distortion and mismatch in channels as well as what was causing the crossover distortion. Great video series! I know by the time you finished reversing this and drawing the schematic you were ready to button it up lol.
I think one of the clips was missing when I went to edit the video. It just proves that when it comes to video production, I should probably keep my day job ;) As for the repair, there were two main problems: First was the two potentiometers at the output of the MPX decoding circuit. They were hugely out of tolerance. Replacing them allowed the unit to have proper stereo separation. Second, was the fact that over half of the resistors in the buffer amp section were also hugely out of tolerance. Replacing them made the biggest difference and most importantly, brought the right and left channels into equal amplitude. Prior to replacing the resistors, the buffer amp had low gain. By the time you adjusted the output from the IF stage high enough to drive everything, it would cause distortion of the signal. After I repaired the buffer amp, I turned the output from the I.F. board down and everything fell into place. I've never serviced a receiver with so many faulty components before! As there was so much wrong, it was death by a thousand cuts. No one problem caused all of the issues. Thanks for the comment! I hope that fills in for what the video was lacking.
Sorry if these were already asked but do you think is was a one-off prototype which would explain the oddities and absence of perfectly matching schematics? Also, was this a “labor of learning” or do you think the parts cost and hours spent could have been justified in light of the value of the unit on the market today as a vintage piece?
My father was an electrical engineer. I did not follow in his footsteps so I do not have knowledge. But that schematic looks awfully complex, alot more than need be.
Wait. So what fixed that amplifier section? Removing the cap between the two stages? I think my comment on the first part about dumping this in the garbage was correct. So many problems. But I’m glad you stuck with it. I learned a lot. I especially liked the FM diagnosing. Thanks!
Here's the response I left for another viewer who asked the same question: I think one of the clips was missing when I went to edit the video. It just proves that when it comes to video production, I should probably keep my day job ;) As for the repair, there were two main problems: First was the two potentiometers at the output of the MPX decoding circuit. They were hugely out of tolerance. Replacing them allowed the unit to have proper stereo separation. Second, was the fact that over half of the resistors in the buffer amp section were also hugely out of tolerance. Replacing them made the biggest difference and most importantly, brought the right and left channels into equal amplitude. Prior to replacing the resistors, the buffer amp had low gain. By the time you adjusted the output from the IF stage high enough to drive everything, it would cause distortion of the signal. After I repaired the buffer amp, I turned the output from the I.F. board down and everything fell into place. I've never serviced a receiver with so many faulty components before! As there was so much wrong, it was death by a thousand cuts. No one problem caused all of the issues. Thanks for the comment! I hope that fills in for what the video was lacking.
xraytonyb Hey I make videos too and I know how much work it takes. No apologies needed. Yes, that clears it up. Thanks. Very strange to have so many resistors out. Ha, death by a thousand cuts! An appropriate description. Hopefully the remaining parts will behave and it will last a long time.
(@33:36) if you look at Q6/Q7, you’ll notice they’re biased the way I would expect to see for a 1-transistor stage; namely, a voltage divider composed of R33 & R34 (for Q6) between the positive supply rail and the negative supply rail (the big, thick line). But if you look at Q4/Q5, their only bias is w/regard to the positive supply rail. Q4 and Q5 would, I think, benefit from a resistor from their base to ground, and selected to bring the transistor about midway on the linear portion of the device curve with 0 volts AC (signal) at the base. Ditto for Q5. Do the schematics for similar models show these pre-driver transistors being biased with a voltage divider? That might give you a ball-park value of resistor to use, or experimentation with a 10k pot or a resistance substitution box, until a nice sine wave at the base produces a nice sine wave (but 180 out of phase) at the collector with a larger amplitude, and an in-phase sine wave at the emitter that’s very close in amplitude to the input signal. Or is there an actual resistor between the base(s) and ground that’s not shown on the schematic?
Wow that was some serious sleuthing. It was supposed to be DC coupled and the schematic did not agree with what you were working with. Your skill is always amazing me Tony. Great Job! Holly Moly!
8:40 - Tony, just for sh*ts and giggles, it could be interesting to see how LINEAR those off-value pots are through their range! :) (that is, if you haven't thrown them away, already :) )
I actually Did go through it again. Better the second time. I believe the look of your job here, might have been inspired by the trashy site you were presented with. Looks nice.
I thought that it was going to beat you Tony and that would have made number two! But I guess it's just the quasi complimentary Amplifier that beat you! The one that you didn't fix! Quasi 1 Vs Tony 0. The Kenwood didn't stand a chance LoL... Even though it put up a good fight.
If anybody wants some old vintage receivers hit me up. Got some old kenwoods sansui etc. they need work but you can have them for free. I just dont have time and money to get them going. I live in fairhaven ma
![Electronic Circuitry Diagnosis And Fault Finding! [Repair]](http://i.ytimg.com/vi/LC7OjuYAOQE/mqdefault.jpg)
Thank you Tony for sharing your extensive knowledge with us and always clearly explaining how you go about troubleshooting the various faults you find. Clearly you know your stuff and you are an EXCELLENT teacher, in my humble opinion! God bless you and I look forward to "our" next project, with you at the helm. Stay safe and healthy Tony.
Excellent, thank you Tony. I'm learning much from your patient and methodical approach. Also loved the shout out to Big Clive, it always interests me that CZcamsrs with very different styles but a fundamentally common interest watch each other's channels. The sense of diversity and community is when the internet is at its absolute best, and fortunately this far outweighs the more negative aspects.
Thank you Tony for another informative series of videos. I'm just a rank beginner in this subject and I have to be honest and say that I don't understand 90% of what you are talking about but I find your (lectures) so interesting and I watch every episode. You certainly missed your calling as a teacher because you are very inspiring.
HE didnt miss anything, he has more students and has taught more people in a shorter time then any full time teacher I know.
this was an awesome repair series on the kenwppd ..and why im a fan i guess of your channel, i have learned a bunch of things i would not have considered before and have added to my knowledge base.. great perserverance ..many would have either tossed it or scrapped it..you fixed it thats the difference..cheers
Glad to hear it!
Great Job ! The final resulting waveforms where simetrical , almost perfect .It was a pleasure watching this project ! :)
Thanks Tony for all your hard work and I think that reciver is blessed to have owners over the years that loved it and tried to keep it alive 🙂. You would have made an excellent medical Dr. I think 😇
very interesting and informative series,it takes a special kind of person with such dedication to bring vintage gear back from its previous state,thanks for sharing brother!
That was one heck of a job to complete. I own a 35 year old Kenwood component style system and it's still working like new as far as I can tell. Some rotary controls have a little dust in them but not bad. This one has a digital FM tuner. I've owned this system since it was brand new in 1985. Anyway, good job on that Kenwood receiver!
What a series. Incredible
Wow, what an epic production that receiver was. But in the end, it turned out nice, I love the look it has with the dial lights and the indicators for FM Mono/Stereo and the functions selected.
Excellent Series. Very Educational and entertaining. I certainly don’t have your patience. 😆 Thanks Tony
Neither do I, anymore ;)
xraytonyb I think patience is inversely proportional to one’s age. Although it’s hard to go past 0%, but I’m going for it.
Well congratulations on yet another great restoration project completed.
Good to hear that some of the comments actually was correct and helpful for you.
No doubt that you would have made it alone also considering your knowledge in this field.
It's really a challenge without a proper service manual or correct schematics. Well done.
Thank you!
Nice job Tony!!! Sounds grate.cheers
Tony, you are quite the teacher in my eyes...I have learned much in this adventure and it is safe to say, I will without hesitation, stay away from the Kenwood TK-80U if one ever crosses my path...😁
Nice work sounds great
Just1
NICE SAVE!
Thanks for the nice detailed explanation
Thanks, Sergio. Good to hear from you! Stay well!
I had a stereo amp from this era and I do not recall a hmm at very low volume. It was awesome and wish I still had it to work on today.
You deserve a holiday after this one, either that or a spell in the funny farm : ) Most of us would have given up ages ago and chucked the bugger in the bin. Hats off to you, amp fixer to the gods....DA.
Very informative video. Enjoyed it very much thank you.
Tony,
I’ll have to nickname you Calypso, (after the John Denver song) .. “Aye Calypso, the places you’ve been to, the things that you taught us, the stories you tell” ...
Ur Amazing .. I think I would have bailed ...
That was a incredible feat.
It looks so much like my kw-55 I think they took the same faceplate, control and knobs. Except the kw-55 is a all tube unit with 17w channel EL84 pp. It sounds good but could be better. The fm receiver is very sensitive.
@xraytonyb So 30-40 years later, As of today, We replaces Electrolytic Capacitors And known bad Transistors, Tony oh know! Did you discover that in the next ten years we will also have to add to Resistors & Germanium Diode???? I have a Pioneer RG-02 re-Build Kit (caps,trans) and still has problems, After this video I will replace the 4-germanium diodes, I hope it fixes it.(Only thing left are Diodes,ceramic,see through capacitors and resistors Lol)
VR3 looks to be some kind of blend control. You can reduce the noise by mono-ing the high frequencies. (Most of the noise is hiss in the L-R signal, resulting in hiss that is out of phase in each channel.) But too aggressive and you lose separation. C26 should probably be a non-polar cap.
Hi Tony, this stands as a tribute to your exemplary knowledge and patience!
I fail to see how you could have conveyed so much valuable information in a shorter video - perhaps some folks don't want information, just simple answers?
I had no problem with the length. I'm glad for the breaks and, with a little patience, when you consider the incredible enjoyment with your audience, isn't it really worth it? I would go through it again! Thanks to all!
Tony, Unless I missed it, you never told us what the issue was in the buffer amplifier after going through it and reverse engineering it. You said you flipped two of the capacitors so the polarity mached the schematic, and that the two stages were directly coupled. But I didnt catch what exactly was causing the distortion and mismatch in channels as well as what was causing the crossover distortion. Great video series! I know by the time you finished reversing this and drawing the schematic you were ready to button it up lol.
I was going to ask the same thing - what fixed it??
I think one of the clips was missing when I went to edit the video. It just proves that when it comes to video production, I should probably keep my day job ;)
As for the repair, there were two main problems:
First was the two potentiometers at the output of the MPX decoding circuit. They were hugely out of tolerance. Replacing them allowed the unit to have proper stereo separation.
Second, was the fact that over half of the resistors in the buffer amp section were also hugely out of tolerance. Replacing them made the biggest difference and most importantly, brought the right and left channels into equal amplitude. Prior to replacing the resistors, the buffer amp had low gain. By the time you adjusted the output from the IF stage high enough to drive everything, it would cause distortion of the signal. After I repaired the buffer amp, I turned the output from the I.F. board down and everything fell into place. I've never serviced a receiver with so many faulty components before! As there was so much wrong, it was death by a thousand cuts. No one problem caused all of the issues. Thanks for the comment! I hope that fills in for what the video was lacking.
Kevin C you asked this for me, I was going to ask Tony but now I understand.
for .9% total harmonic distortion it sounds fantastic
Those odd value capacitors in that module like 510pf, and the others are available from mouser.
I love "the reason being is."
Enjoyed the series. Couldn't you use a CZcams music source to modulate the aux mod input of your signal generator?
I could, but I like all of you and wouldn't want to submit you to that ;) Of course, it would be amusing to modulate "Toe Jam" through the HP8657 :)=)
Sorry if these were already asked but do you think is was a one-off prototype which would explain the oddities and absence of perfectly matching schematics? Also, was this a “labor of learning” or do you think the parts cost and hours spent could have been justified in light of the value of the unit on the market today as a vintage piece?
Available with the fantastic Big 5 Warranty! 5 seconds or 5 feet out of the driveway.
Whichever comes first!
With old gear like this I always take it that the Warranty expires at the point of sale.
In construction that is the bumper to bumper warranty. Once one bumper passes and the second is out of site, that warranty is over.
My father was an electrical engineer. I did not follow in his footsteps so I do not have knowledge. But that schematic looks awfully complex, alot more than need be.
Ditto...
Wait. So what fixed that amplifier section? Removing the cap between the two stages? I think my comment on the first part about dumping this in the garbage was correct. So many problems. But I’m glad you stuck with it. I learned a lot. I especially liked the FM diagnosing. Thanks!
Here's the response I left for another viewer who asked the same question:
I think one of the clips was missing when I went to edit the video. It just proves that when it comes to video production, I should probably keep my day job ;)
As for the repair, there were two main problems:
First was the two potentiometers at the output of the MPX decoding circuit. They were hugely out of tolerance. Replacing them allowed the unit to have proper stereo separation.
Second, was the fact that over half of the resistors in the buffer amp section were also hugely out of tolerance. Replacing them made the biggest difference and most importantly, brought the right and left channels into equal amplitude. Prior to replacing the resistors, the buffer amp had low gain. By the time you adjusted the output from the IF stage high enough to drive everything, it would cause distortion of the signal. After I repaired the buffer amp, I turned the output from the I.F. board down and everything fell into place. I've never serviced a receiver with so many faulty components before! As there was so much wrong, it was death by a thousand cuts. No one problem caused all of the issues. Thanks for the comment! I hope that fills in for what the video was lacking.
xraytonyb Hey I make videos too and I know how much work it takes. No apologies needed. Yes, that clears it up. Thanks. Very strange to have so many resistors out. Ha, death by a thousand cuts! An appropriate description. Hopefully the remaining parts will behave and it will last a long time.
(@33:36) if you look at Q6/Q7, you’ll notice they’re biased the way I would expect to see for a 1-transistor stage; namely, a voltage divider composed of R33 & R34 (for Q6) between the positive supply rail and the negative supply rail (the big, thick line). But if you look at Q4/Q5, their only bias is w/regard to the positive supply rail. Q4 and Q5 would, I think, benefit from a resistor from their base to ground, and selected to bring the transistor about midway on the linear portion of the device curve with 0 volts AC (signal) at the base. Ditto for Q5. Do the schematics for similar models show these pre-driver transistors being biased with a voltage divider? That might give you a ball-park value of resistor to use, or experimentation with a 10k pot or a resistance substitution box, until a nice sine wave at the base produces a nice sine wave (but 180 out of phase) at the collector with a larger amplitude, and an in-phase sine wave at the emitter that’s very close in amplitude to the input signal. Or is there an actual resistor between the base(s) and ground that’s not shown on the schematic?
my magnavox had a low output on one channel and i discovered 5 or 6 resistors were way out of tolerance
Wow that was some serious sleuthing. It was supposed to be DC coupled and the schematic did not agree with what you were working with. Your skill is always amazing me Tony. Great Job! Holly Moly!
Could not have said it better. Must be Holmes!
8:40 - Tony, just for sh*ts and giggles, it could be interesting to see how LINEAR those off-value pots are through their range! :)
(that is, if you haven't thrown them away, already :) )
Do you actually have any hair left after this project?
Losing some hair would be an advantage, at this time! The barbershop is still closed! :)
@@xraytonyb I cut my own and have done for years.
@@bulwinkle So do I!
Great job and very informative. Can´t be long enough; ignore the idiots!
I usually do. Living in a rural area, I have gotten used to stepping over such things. Troll droppings are no different ;)
Talk about copy right strikes. Yep, I heard some Alabama and Kiss in there :-)
I actually Did go through it again. Better the second time. I believe the look of your job here, might have been inspired by the trashy site you were presented with. Looks nice.
I thought that it was going to beat you Tony and that would have made number two! But I guess it's just the quasi complimentary Amplifier that beat you! The one that you didn't fix!
Quasi 1 Vs Tony 0.
The Kenwood didn't stand a chance LoL... Even though it put up a good fight.
The output stage of this amp (that Tony was working on) was quasi-complementary was it not?
30:05, shout out to bigclive!
The morning routine before work: Coffee & BigClive video!
Moral of the story: Stay away from old, low-end audio gear, it ain't worth it
Well, that high-end Sansui receiver was no PICNIC! :) (the one with the frequency response ranging from DC to Slightly Yellow ! :)
a BC547 is similar to a Sylvania ecg123
If anybody wants some old vintage receivers hit me up. Got some old kenwoods sansui etc. they need work but you can have them for free. I just dont have time and money to get them going. I live in fairhaven ma
I'am looking for a Yamaha R-500??
@Etienne No i dont. But got alot of old tube radios from the 40s and 50s. They do need caps. You can have them.