Kenwood KR 4600 Receiver - Repairs (Ep. 112)

A classic Kenwood. Listening to this receiver was a treat

[@johnabalos1455]

Have one of these that I bought when I was 22 yrs old in 1976 , still have it an it plays great!! The blue lights on orange still look amazing!!

[@Eduardo_A_dC]

Found the service manual... now to alignment etc. Replaced all illumination with new warm LEDs but still looking for a replacement dial pointer. The LED at the tip of the pointer is burnt. KR4600 is a very nice receiver. Thank you for the video!

[@mikeydudez120]

First Kenny on the bench! Always liked the look of this particular model. 🤩

[@TrevorsBench]

I was impressed by the listening tests. Really a solid, good sounding receiver

[@SoundofSilence-45]

@@TrevorsBench Hey Trevor, I have a Kenwood KR-4140 that does not power on but is cosmetically in nice condition. I changed the fuse in the back but still nothing. Do you know what could possible be preventing this unit from power on?

[@ian-c.01]

That's the kind of catastrophic fault that gets everyone scratching their heads while watching the video ! The most interesting part about it is how you fixed the issue, most of us wouldn't know where to start !

[@steveoszman8746]

Great stuff, don't sweat the petty stuff, I am really impressed in your ability to bring life back to these cantankerous old electronics.

[@TrevorsBench]

Thanks, they are a real treat to listen to after I'm done. Too bad I can't share the sound quality with you viewers too

[@vintagesimpilot2623]

I have a KR 5600 which is probably nearly identical to this model. Most of the pots are scratchy when I turn them, probably something I can do with Deoxit. However, I also need to replace the faceplate illuminator bulbs which I can't figure out how to extract without breaking something. If I could find a guy like you who really knew what he was doing, I would gladly pay to have it all re-capped, tuned up and 100% operational. I suspect it would cost more than the original price when I purchased it in 1977.

[@RobsFixitShop]

Very enjoyable fix especially the replacement with a darlington

[@TrevorsBench]

Thanks Rob

[@bradfordaudio]

Love these Kenwoods. Great looks.

[@TrevorsBench]

I'm warming up to them too, really impressed with the sound quality during the listening tests

[@jacknjill3000]

I have the Kenwood KR-5600 and it looks and sound incredible. Just the phono setting is not working unless I put the knob off to the side a little. I think the phono and and speaker connections need to be detoxed and cleaned.

[@frankgeeraerts6243]

You did it again , ...you're one of a kind and I think many agree with IT Trevor !

[@bigmsound]

Great repair and modification. You can't blame yourself for the sudden magic smoke issue in the power amp. It could be that an unobtainable output transistor just decided to suddenly give up the ghost and cremate other components in it's path. This receiver is over 40 years old and components can suddenly fail catastrophically . The charm is the way that you improved an out of the box solution, and made the old Kenwood run as good as new or maybe even better .

[@TrevorsBench]

Thanks

[@alexismethenitis]

Thank you for another great video, Trevor.

[@TrevorsBench]

Thanks for watching Alexis

[@fontasgenave7066]

Very nice unit! Would have like to hear it playing like you usually do at the end. Anyway’s… really enjoyed watching your specialist repairs, thank you for sharing!

[@richardkelsch3640]

If I remember correctly, raw FM multiplex output was for things like Dolby FM and DBX FM decoders for areas that had them, or were experimenting with them. Having the raw unprocessed audio signal allowed for this processing without the de-emphasis messing with it. The Dolby FM and DBX FM decoders would also decode stereo on their own.

[@jacknjill3000]

I have the Kenwood KR-5600 and love it. The only issue I have is when I use my record player and put on phono (it has 2 phono inputs) I have to kind of put the button btwn the phono and radio and jot a big issue and can fully use. But recently in phono mode the sound was only coining from one speaker, so I thought my record player had a channel out. But when I moved around the speaker wire and phono jack, it kicked back in and the sound came back to the right speaker and now both working, So I’m thinking to get some detox and spray the contacts to keep the contacts clean and working . I know these are a pain to work on bc of the inner works design and I’m not even going to attempt it. I hope more ppl. start working on vintage stereos and open repair shops to take these vintage units fir repair and maintenance bc they are built solid.

[@apolinarmartinez5723]

Great video, I enjoy your videos, could you talk more about replacement output transistors from old to new ones? It was really interesting to me, thanks, regards

[@TrevorsBench]

I'll try to keep this in mind next time I have dead outputs

[@dorelgogu8631]

Those pairs of output transistors are troublesome. I had to replace them on every amp I worked on. How about a beta of 3? About the bias, I never bother with the emitter resistors. I always check the base to emitter voltage and set it for somewhere around 550mV. Keep up the good work and thanks for the videos!

[@TrevorsBench]

You guys are just confirming what I was thinking all along. This isn't a very well designed amp. It sounds fine but is maybe unstable? Thanks.

[@alainlatour4629]

Very nice set-up and great way to resolve the output transistor problem. I am working on a KR 5600 his bigger brother and since i don't do that often and getting myself pretty old... to remove the audio board, how do you deal with the wrapped around wire over post? Unsoldering the post from beneath or what? Does not seem so easy to get the board out... Thanks again, very nice video!

[@TrevorsBench]

If I remember correctly, I unwrapped the wire from the post. When I re-installed the amplifier, I just soldered the wire back to the post. There were only about 10 wires that needed to be worked on like this so removal/install of the amp board wasn't a big deal

[@alainlatour4629]

Thank you Sir. Like very much watching your video. @@TrevorsBench

[@anthonypopovic7626]

Well, i had a working kenwood KR-4600. I was attempting to set the bias. I had one lead of my volt meter connected to the R53 emitter resisitor. I was trying to figure out how exactly, i'd measure the bias - I clearly, didn't understand the instructions since i put the other lead of the volt meter to the QM 21 transistor. Well the transistor sparked and the unit shut down and wouldn't turn on. I removed the bottom and found a burned out fuse. I put a new correct fuse in, and turned it on. Poof! blew another fuse. I'm wondering if i only blew the transistor, or everything else you've shown here.

[@TrevorsBench]

Well, all bias readings are taken across a emitter resistor. Did you have the service manual to reference? A spark suggests something slipped and shorted the transistor. Taking a voltage measurement will not kill your amplifier or cause a spark, a short will. Another possibility was you had cracked solders and moving the transistor caused the failure

[@anthonypopovic7626]

@@TrevorsBench I did have the service manual. The output transistors sparked when I touched the lead of the volt meter to it, with the other lead connected to the emitter resistor. When I connected both leads to the emitter resistor it read close to zero despite working and producing sound. I had both leads connected to one resistor and it was close to zero.

[@anthonypopovic7626]

@@TrevorsBench also it’s the fuse underneath the receiver near the power supply that is burning. If that’s for the speaker relay then maybe it’s the bad solder joint you mentioned.

[@TrevorsBench]

@@anthonypopovic7626 Then maybe the meter was set up to read something other than volts because the DC volts range of your meter would never create a spark. Does your meter have a diode function? if so start measuring the junctions of each transistor to test for shorts or opens. The transistors you want to check are the drivers and outputs. Plus, check the emitter resistors for opens. Start there to find out where the damage is

[@seano51]

Hello, thank you for making this video. It has been helpful as I sort out my KR-4600. Just one question, currently I'm seeing 50mV dc offset out of my left channel. Is this acceptable? The offset is definitely coming from the amplifier stage and it persists even after performing the bias adjustment.

[@TrevorsBench]

50mv is not a concern, enjoy your Kenwood

[@seano51]

@@TrevorsBench Thank you

[@bradfordaudio]

MPX output was probably for a Dolby FM decoder.

[@jeffersonpaula]

hi how are you, I like your videos and you are very professional , I have a Pioneer SA-508 need to repair bud I am living out off US , it turn on but sound like fries and after stop and working properly

[@vcp93]

Hey Trevor, "Joe N00bie" here. Just found your channel and recently subbed. Love that lazy-Susan you have there. Did you buy that or make it? Cheers! 👽🖖"Na-nu"

[@TrevorsBench]

I bought the turntable at a flea market, added a piece of plywood to finish it off

[@GeorgeLykissas]

Excellent video! And so helpful! Could you please tell what might be an average temperature of this receiver when powered and at half the volume? I have the same one, and it gets rather warm, but I don't know if that is expected or a symptom of malfunction. I have connected a pair of Wharfedale 9.1 6 ohm speakers. Thank you so much in advance!

[@esligaeremijn983]

Hey, Can you explain how you get the board switch out of the unit? It’s not that clear for me. I have the same issue on my receiver. Thanks!

[@Willow5673]

Can you reach the control knobs through the back end to clean/detox them?

[@TrevorsBench]

Honestly, I can't remember. I do know the input selector section is at the back and a real pain to get to. I remember disassembling quite a bit just to inspect and clean the switches

[@Willow5673]

@@TrevorsBench hey thanks for the reply! Finished her up couple days ago. Was a pain in the *** but got it done! She’s working perfect! Thxs

[@TrevorsBench]

@@Willow5673 Awesome, well done!

[@jacknjill3000]

@Willow5673, were you able to detox with just from the back? Bc that’s what I want to do with my Kenwood KR-5600. My phono switch seems to not engage when flip to, but sort of work when putting the switch a little off the phono mark. Plus, my phone play was coming out of only the left speaker, but moving the speaker wires and phono input jack helped. But it would like to do a simple clean and detox to not further this issue.

[@JerryPemberton]

Where are you measuring for the 17-18 volts when taking the measurements near the end?

[@gillanland]

At the speaker connectors.

[@Films-vm4uh]

Hello, I have this same unit. Bought a few years ago. Sometimes when I’m listening to an input, I start getting static and the sound is muffled. I then go and wiggle the knob or flip to another input and then back and that clears the problem. I had it at a repair shop who stated they couldn’t fix the problem. Any idea what might be causing that and how I could fix? It’s just annoying more than anything. Thank you

[@TrevorsBench]

This kind of failure is very common and typical of vintage stereos. Oxidation on the contacts of switches, potentiometers and relays cause channel drop outs and scratchy noises. For switches or relays the fix is disassemble the offending switch and clean and polish the contact surfaces. For volume and other controls they can be cleaned and treated with products from a company called Caig. Shops won't do this level of work and only want to replace the offending part which, by now, are unobtainable. Surprisingly, working the controls and daily use will clear switches and pots of noise somewhat. If they are really bad, they need extra help. Another problem in vintage stereos is cracked solders at the joints for these switches, pots and relays. Inspect and re-solder as necessary is the fix

[@Films-vm4uh]

Thank you so much for the response. I will try exercising the knobs and buy that product to make the contacts better. Otherwise, it’s not that big an issue. Thanks

[@Kevin-lp3pu]

I'm currently looking to revive my KR-4600. How much would a repair like this cost and how long could it take? I'm trying to find someone to work on it but it's been difficult.

[@Kevin-lp3pu]

Can you work on mine? It's in need of some attention.

[@thedistortedguy]

Himan , emaild id plz . Cant get it in ur about section