Kenwood KR-4070 Issue

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by dontmindme, Nov 20, 2011.

  1. dontmindme

    dontmindme Creature

    Messages:
    1,117
    Location:
    Nebraska
    I've got a KR-4070 that, sometimes powers on fine. Other times everything but the tuner and signal meter light, then if you tap on the top, the light comes on. Other times when you power it on, the lights kind of flicker at almost half power with static, then a few seconds later, it all comes on. I've cleaned the main on/off switch, but still have the problem. The power switch also is the speaker A and B and AB switch. When I go from speaker A to AB, the A speakers don't come on. Should they? And if not, is the switch a problem? Thanks for the help.
     
  2. dontmindme

    dontmindme Creature

    Messages:
    1,117
    Location:
    Nebraska
    Upon further investigation, I've read that the power switch that's part of the speaker selector switch is prone to failure. It may have an additional set of contact on the underside? I've read that you can turn the switch over and re-solder the connections as the switch has an additional set of contacts. How do you remove the switch?
     
  3. Watthour

    Watthour Electron Rancher - JS3600

    The switch may or may not have dual contact pairs, but it doesn't matter much. Once you gain access to the switch even the carboned contacts can be clean effectively and returned to service:

    [​IMG]

    As for access to the power switch, it's a bit of work but you can maximize your return on labor input by repairing and servicing a few other items along the way.

    Remove the knobs and faceplate screws, remove the two fixture nuts from the control stems, then remove the faceplate.

    [​IMG]

    Unstring the tuner indicator. It's best to wrap the tuner VC drum with a piece of masking tape before beginning so that you won't have to completely restring the tuner. Release the tension on the string by guiding off the front rollers then remove the tuner indicator pin carefully. Set that all aside.

    Remove the bezel lamps, then remove the front bezel screws and control fixture nuts, allowing you to remove the bezel.


    [​IMG]

    Remove the fixture nuts and remaining front frame screws, then remove the front frame:

    [​IMG]

    That should expose the power/speaker control as shown. Carefully straighten the metal tangs holding the power/speaker switch control know from the switch array, then pull the knob forward:

    [​IMG]

    Remove the switch link bar, carefully bend the metal latches holding the power switch into the frame, and lift the switch upward and out:

    [​IMG]

    The switch halves are not glued nor fastened so they will simply pull apart. Be aware of the center cam position when opening the switch so that you can assemble it in the same position. Once cleaned, reassemble in reverse order. Try to be careful with inserting the link bar through the speaker switch wafer since it is a fairly frail item.

    You can clean all the parts along the way, including the bezel, lamps, front glass, etc. This is a good opportunity to center the tuning indicator if it is no longer exactly on station, and to clean controls, lubricate the turning string guides, replace a failed STEREO indicator lamp, beezwax the string, and generally clean up an otherwise inaccessible area of the main amp board.
     
  4. dontmindme

    dontmindme Creature

    Messages:
    1,117
    Location:
    Nebraska
    Wow, thanks for the help! I'm not an electronics guy, but I'm going to give it a try. With your pictures and instructions, I may be able to get it done. The only part I'm uncomfortable with is the tuner string.... I've had the front apart already and cleaned the pots, switches and glass and such. I guess I'll dive a little further into it this time. Thanks again, great group of guys on this site.
     
  5. dontmindme

    dontmindme Creature

    Messages:
    1,117
    Location:
    Nebraska
    Finished! Went just like you said, there was an additional set of contacts on the other side that were brand new. The only thing that didn't make sense was the shaft that goes through the assembly. What holds it in place? Mine seems to be more loose than I would like. Once I put it all back together, what keeps it from sliding out the back side.... It has about 1/2" before it would hit the molex plug behind it. It seems over time it would work its way out or back. The tension on the tuner string was a little scary going back together. It seemed a little tighter going back on. I took pictures before I pulled it apart, so I know I have it together the same way. Anyway, thanks again. This was a first for me. I've cleaned pots before, but never pulled one apart that far. Without your help or pictures, I wouldn't have gotten it done. Happy Thanksgiving!
     
  6. Watthour

    Watthour Electron Rancher - JS3600

    The only thing holding the flat link bar in place is fear. Even a piece of that extra special yellow plastic oriental tape across the back might have been sufficient when they assembled the units.

    Ironically, I recently shipped one of these (4070) to a fellow AK-er and it was in working order when it left. I was a little surprised at the email I received saying the unit would not power on, but after pondering it a bit I'd guessed that the unit was stacked vertically for shipping and the link must have slipped out as the truck bounced along the expressway. Our next emails crossed in cyberspace within 30 seconds as I advised him to check the switch link and he was informing me that he had removed the lid and discovered that the link had slipped backward. The next time I get into a unit with this type Alps switch I plan to drop just a dab of hot melt glue or small self-adhesive decal onto the back of the black plastic switch cam once it is assembled to prevent this. It should still be serviceable by pulling the link out the front.
     
  7. dontmindme

    dontmindme Creature

    Messages:
    1,117
    Location:
    Nebraska
    So, are you saying hot glue between the power switch and speaker wafer? Or on the back side of the power switch, just attaching the shaft to the black plastic switch cam? I thought about wedging something (foam) between the molex and back end of shaft? At any rate, I don't see how they ever made it from Kenwood to the store to the consumer without a few having that problem... Thanks for confirming something that didn't look right!
     
  8. evallded

    evallded Member

    Messages:
    76
    Hate to be necroposting, but I just wanted to thank Watthour for this tutorial. I picked up my first Kenwood KR-4070 today for 5.00 because it didnt work. I have never worked on anything like this before but just followed the steps, it was all exactly correct, flipped the switch and soldered and it all works like new! Thanks so much.
     
  9. Watthour

    Watthour Electron Rancher - JS3600

    Don't stop there, my friend. Go through the cleanup and testing procedures to make sure the unit remains reliable for another few decades. They are a nice little mid-fi receiver with pretty good punch on efficient speakers.

    The output transistors should be re-greased for good heat dissipation, then the DC bias should be checked/set since the output transistors are about unavailable any more.
     
  10. rastavibes

    rastavibes New Member

    Messages:
    7
    Hello,

    I have a nice Kenwood kr-4070 that used to be my main amp. I dont want to dispose it, it looks great. So I wonder if I could use it as the subwoofer amplifier.

    I am planing to use speaker level to rca converter from my actual tube amp outs, with a passive low-pass in the middle, to feed the aux in of the Kenwood.

    What do you think? Should I go on with it?

    Thanks a lot!
     
  11. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    824
    Location:
    Vancouver, WA
    I just did the old power switch flipperoo on a 4070 I picked up. I found this thread after the fact. The only real disassembly required was to remove the top cover. Once it's off, remove the plug connector right behind the switch by pulling up gently - no tricks or hidden lock tabs. Once that's out of the way you'll see the little aluminum bar sticking out the back side of the switch. Turn the switch to the OFF position with the front panel knob. Grab the bar with needle nose and it'll come out the back pretty easily. The inductor coil is kinda in the way, but not really. Then bend the four tabs that hold the switch to the bracket out of the way and pull the switch out.

    The tricky part for me was getting the switch in the correct position before reinstalling it (rotated 180) There are no internal stops in the switch. You can rotate it 360 and it'll just keep going. For about 359 of the 360 degrees of rotation the switch is closed. I moved it to the very small spot where it is open and stuck it the bracket, then reinserted the metal bar, kinda wiggling it til it seated through the speaker wafer and into the shaft. Checked with a continuity checker to make certain it was still open, then bent the tabs back to lock it in place. Resoldered the two big wires, and also added a safety cap which Kenwood hadn't included on mine. https://www.digikey.com/product-det...merica/DE2F3KY103MA3BU02F/490-9487-ND/4421303

    While in there cleaned the speaker portion with Deoxit D5. Works like a champ.

    P1011160.JPG

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    P1011163.JPG
     
    Last edited: Aug 23, 2017
  12. CharlieBee

    CharlieBee Well-Known Member

    Messages:
    855
    Location:
    Baton Rouge, Louisiana
    Do not quit with just repairing that switch.

    I have a KR 4070, with the dreaded power switch and speaker selector switch combo also. This is a very poor design. It is a perfect candidate for switchable power switch that will take all wear off the combo switch.

    I have a switchable power switch for all my systems and plug in all CD, TT, RTR etc into it also. That saves all the switches from wear and tear and I can unplug all of them by just unplugging the switchable power switch. Why unplug them, well for the ultimate in lightning and power surge protection.

    I find switchable power strips cheap ,at estate and garage sales, usually a dollar or two.

    Charlie
     
    Last edited: Sep 12, 2017

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