The Kenwood KR-9050 is Exposed

Endzone

Active Member
So far I've discovered a few problems (thanks to help from members on the board) that have been fixed:

1. D16, D17, & Q10 on tuner board defective causing tuner power supply to fail.

2. After much troubleshooting found out why the right channel would not work. In the tone control board there was a cracked solder joint on one side the balance control pot where the input signal entered. This was not visible with the tone control board installed under the chassis.

3. Schematic had wrong pin out for right channel/left channel input to tone control board. One pin was skipped on the board, but that change was never made on the schematic which threw every pin off by 1 pin.

4. Aux, Stereo, and IF indicators lamps are burned out and need to be replaced.

A few pics:


Q10 and associated transistors for voltage regulator on tuner board not yet replaced.
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Stereo mode switch, dubbing & monitor A/B & mode switch​
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Bad solder joint very lower front going to balance pot was cracked.​
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left/right input to tone control board. Pin 2 skipped but not on schematic​
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Tone control board--low/mid/high pots and volume and balance pots​
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Lamps for AUX, Stereo & Narrow IF are burned out. Anybody know where I might be able to get these?​
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Unit before disassembly. Found unit in garage and I think it was being used as a prop.​
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Nice work. I hate it when there's undocumented/incorrect info on the schematic. Looks like quite a few of those joints could use some fresh solder.
 
You said it. KR-9050 should make everybody's Top 7 ever vintage receivers list. Outside of some touchy switches mine performs great.

200 wpc/250@4 ohms
Toroid is bigger than a SX-1250's. 1200 max draw.
Tuner is better than a KT-8300.
Sankens just like the AU-X1. Well the AU-X1 has 6 instead of 4 but hey what do you want for only $1200 MSRP in 1979?


I'm probably going to give the lights a cool LED makeover. The little burn marks on the old lights' reflection paper make me nervous.
 
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beautiful piece! great job... I still have a Denon avr-5700 that was given to me that needs some work, I wish it was built simple like that Kenny. man it's gonna be a bitch to fix.
 
Welcome to the Kenwood monster party. Outside of the 9600, they fly under the radar - and while the 9600 is well-known, it's still a bargain at it's power level. The 9400 and 9050 are often downright cheap compared to comparable equipment.
 
I have a 9050 as well. Mine won't power up.

The seller stated that it was on and working when there were some power
problems in the area that caused the house electric to turn off and on three
times rather abruptly.

On the third time, the receiver didn't come back up.

Haven't had the chance to dive feet first into it yet.

Scott
 
My 9400 wouldn't power up when I got it. Half of the power switch was vaporized. I soldered the wires to the other side of the switch and it works fine. I use a timer to turn it on and off, though.
 
I removed, opened, and cleaned my power switch pieces. Silver contacts on a rocker -- Alps brand. All the front switches can use it, particularly those not used frequently like the Mono/Stereo/Reverse.

The wrong cleaning agent, and power on too soon before dried, can vaporize such.

Flipping over the rocker contact to the unused side cured it! The first side was pretty fried.

Replacement of all parts of inrush current limiter would be best. I turn it on with a separate power strip, so the relays still employ the time-delay but the switch itself is less stressed.
 
Have a kr-9050 too, really a nice beast
Had a few problems to work thru, Out of tune FM, Stop for tuning gang gear was missing, Lot of lamps needed replacement, Still have a dark area on the top of meters but am ok with it, and a very long start time till protection relay clicked on, see this thread if you suspect a problem with yours
http://www.audiokarma.org/forums/showthread.php?t=201096
A word of warning, There are some terminals that stick up high just waiting to short out your VU meters, I did this with a can of cleaner and power on, Had to replace the meter driver IC cause of my mess up Good luck
 
Have a kr-9050 too, really a nice beast
Had a few problems to work thru, Out of tune FM, Stop for tuning gang gear was missing, Lot of lamps needed replacement, Still have a dark area on the top of meters but am ok with it, and a very long start time till protection relay clicked on, see this thread if you suspect a problem with yours
http://www.audiokarma.org/forums/showthread.php?t=201096
A word of warning, There are some terminals that stick up high just waiting to short out your VU meters, I did this with a can of cleaner and power on, Had to replace the meter driver IC cause of my mess up Good luck

Thanks for the info. I'd love to go through the alignment procedure for the FM tuner, but I really need a unit like a IFR 1200S or something similar to do the test. This FM tuner is really different that what I'm used to in the HF radio world. The phase detector does not appear to control a VCO for the 1st L.O. Rather there is an "AFC" circuit that is feedback from the Quadrature detector. The 1st L.O. frequency is primarily controlled by the mechanical tuner. This seems really different than how things are done in the ham radio world where the 1st L.O. is a VCO controlled by the PLL circuit.

I am getting the display lamps from Vintage electronics. They are 8V 250mA and the original lamps are 200mA. I think I might have found a source for the indicator lamps (AUX, Phono 1, phono2, etc.) at MCM electronics.

http://www.mcmelectronics.com/product/25-995&cid=prodCrossSell

Do you know if there are illumination lamps inside the "Peak Detector"? I know there are the 2 red lights.
 
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steveq3t, it may be possible to snag a donor unit for your missing gang screw there. They look the same as the ones in my other Kenwoods but I didn't try to swap them to tell for sure.

Endzone, these were made in that odd twilight era when analog tuner knowledge had achieved a peak and the digital revolution was being touted as a means to achieve ultimate perfection.

Somehow the bean counters lost and the engineeers who cared slipped a great sounding, high-performing, and feature-rich tuner inside a mere receiver. :banana: Sneaky!
 
Boys 'n girls I would like to announce that the AM & FM tuners have been restored. The right channel has been restored. Tuner sounds great--on FM the dial indicator is off by 100KHz. AM is off by 10KHz. Both work good, but I need to get one of those twin lead dipole antennas for FM.

The problem was D16 & D17 shorted & Q10 open on the tuner board. This was the main power supply to the tuner.

The right channel failed because of the cracked solder joint at one end of the rheostat on the balance pot.

All switches and pots have been cleaned. I guess what remains now is to replace all indicator lamps and all display lamps. Half of the indicator lamps and all the display lamps are burned out.

I wish I could align the AM/FM receivers per the manual, but I really need an IFR 1200 or something similar to do that. At the very least I need a modulated sig gen and a frequency counter. I'm sure I can set the offset voltage and bias current in the audio section.

A special thanks to ecluser, Artie, & Fred Longworth for helping me get a better understanding of how the voltage regulator circuit worked in the tuner.



D16, D17, Q10, Q11, Q12, Q13 replaced on tuner board
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Does anybody have this U-pin thingie or a Kenwood knob this size I could buy?
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A room mate just came in and said it would actually receive a Christian rock station on 88.7MHz that he couldn't normally pickup. All I'm using for an FM antenna is a 2 foot long piece of wire. That's encouraging.
 
Hard too remember what lamps i used for the indicator lights. think original lamps are 8v.05amp and run thru dropping resistors, Found a near empty pack of lamps 12v 35ma .12/3mm parts express 070-235, I must have used these. Used the old rubber base
1 lamp is dimmer than the rest because the do not all use the same dropping resistor/ voltage. That is good enough for me. My tuner was far enough out cause some one messed with the trimmer caps on tuning gang, I could not make it worse, Adjusted these for a peak, I do not have good equipment for a good tune up. Only adjusted the rf section.
Tuning gangs at this time were made by alps/alpine, Found a sx-680 tuner gang and used the gear system from it.
I do remember i had a very hard time with that spring tensioned gear to take out the gear lash.
At this time the kr-9050 sits next to my sx-1280 and a technics sa-5760
 
SPL db - Out of curiosity, have you tried turning yours on and leaving it for awhile to see what it does?

I have one that has a power on issue also - it will light up but take upwards of 15 minutes for the relay to actually click on.
 
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