How to take apart an old Kenwood receiver?

ingenieus · 6th August 2011, 10:35 AM

Hi all

I have an old Kenwood KR-55 receiver. It worked well until I decided to hook up a pair of 4 ohm speakers. No problem, but then I got carried away and cranked up the volume. Played for a while and then both channels went silent. I figure that I managed to cook the output transistors. Replacing them and/or anything else that got fried should be straight-forward.

However, when I took off the top cover I was confronted by the mechanics of the tuner section. It's all beautifully made, with a long belt looped over various pulleys for the tuner needle et al. This is where I'm a little flustered. To get to the amplifier section all of this has to come off. How straight-forward is the re-assembly of these things?

I' ve been all over the internet to find a service manual, but most sites returned by the search engines seem to be constructed to lure us there with false promises. This is a phenomenon that is worth a discussion all of its own, but I digress. Other sites promises a manual but they want money for it. Being a tight-wad I'm very reluctant to hand out my card number.

Any general guidelines on taking apart analogue tuners (and putting them together again) would therefore be much appreciated. I can post a picture of the mechanics if that will help.

Zen Mod · 6th August 2011, 10:38 AM

pic or two , are generally helpful

digits · 6th August 2011, 10:40 AM

see if the bottom panel doesn't screw off, manu older designs use an upside down PCB accesable from the bottom. The screws may be in or behind the feet.

ingenieus · 6th August 2011, 11:45 AM

Here is the view from the top. One of the trannies show definite signs of being past its prime.

ingenieus · 6th August 2011, 11:49 AM

Taking off the bottom cover turned out to be straight-forward. Hat tip to digits.

I guess the best approach is to leave the PCB in place and just de-solder things where they are. A bit fiddly but dismantling all of this looks quite daunting.

ingenieus · 6th August 2011, 11:58 AM

The output transistors are 2SD613/2SB633. Now to find equivalents/replacements.

gootee · 6th August 2011, 12:25 PM

Keep in mind that there might have been some matching of transistors that was done.

ingenieus · 12:39 PM

The Sanyo datasheet gives the 2SD613/2SB633 out as 85V, 6A, 15MHz devices. The fT of 15MHz seems hard to find in a TO220 high(ish) current device. Another datasheet from Wing Shing Computer Components Co., (H.K.)Ltd (WHO?) specs it as 8MHz.

About the closest match I've seen so far is the BD911/BD912. Same package and lead orientation (BCE) but 'only' 3MHz.

Matching of transistors? I will have to look into that.

adason · 6th August 2011, 12:39 PM

did you check those fuses first?
replace them if blown and see if it's not just a case of blown fuse

ingenieus · 6th August 2011, 12:44 PM

The fuses are OK. Checked them with my trusty Fluke 77. As the old saying goes, they were protected by the transistors.

6th August 2011, 10:35 AM	#1
ingenieus diyAudio Member Join Date: Apr 2011	How to take apart an old Kenwood receiver? Hi all I have an old Kenwood KR-55 receiver. It worked well until I decided to hook up a pair of 4 ohm speakers. No problem, but then I got carried away and cranked up the volume. Played for a while and then both channels went silent. I figure that I managed to cook the output transistors. Replacing them and/or anything else that got fried should be straight-forward. However, when I took off the top cover I was confronted by the mechanics of the tuner section. It's all beautifully made, with a long belt looped over various pulleys for the tuner needle et al. This is where I'm a little flustered. To get to the amplifier section all of this has to come off. How straight-forward is the re-assembly of these things? I' ve been all over the internet to find a service manual, but most sites returned by the search engines seem to be constructed to lure us there with false promises. This is a phenomenon that is worth a discussion all of its own, but I digress. Other sites promises a manual but they want money for it. Being a tight-wad I'm very reluctant to hand out my card number. Any general guidelines on taking apart analogue tuners (and putting them together again) would therefore be much appreciated. I can post a picture of the mechanics if that will help.

6th August 2011, 10:38 AM	#2
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	pic or two , are generally helpful __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; BAF Forum & Gallery;I'm dumb

6th August 2011, 12:34 PM	#8
ingenieus diyAudio Member Join Date: Apr 2011	The Sanyo datasheet gives the 2SD613/2SB633 out as 85V, 6A, 15MHz devices. The fT of 15MHz seems hard to find in a TO220 high(ish) current device. Another datasheet from Wing Shing Computer Components Co., (H.K.)Ltd (WHO?) specs it as 8MHz. About the closest match I've seen so far is the BD911/BD912. Same package and lead orientation (BCE) but 'only' 3MHz. Matching of transistors? I will have to look into that. Last edited by ingenieus; 6th August 2011 at 12:39 PM.

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6th August 2011, 10:40 AM	#3
digits diyAudio Member Join Date: Apr 2011	see if the bottom panel doesn't screw off, manu older designs use an upside down PCB accesable from the bottom. The screws may be in or behind the feet.

6th August 2011, 11:58 AM	#6
ingenieus diyAudio Member Join Date: Apr 2011	The output transistors are 2SD613/2SB633. Now to find equivalents/replacements.

6th August 2011, 12:25 PM	#7
gootee diyAudio Member Join Date: Nov 2006 Location: Indiana Blog Entries: 1	Keep in mind that there might have been some matching of transistors that was done.

6th August 2011, 12:39 PM	#9
adason diyAudio Member Join Date: Nov 2004 Location: home sweet home	did you check those fuses first? replace them if blown and see if it's not just a case of blown fuse

6th August 2011, 12:44 PM	#10
ingenieus diyAudio Member Join Date: Apr 2011	The fuses are OK. Checked them with my trusty Fluke 77. As the old saying goes, they were protected by the transistors.

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