New to this, troubleshooting help? KR-4200

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by AstroJake, Nov 4, 2018.

  1. AstroJake

    AstroJake New Member


    First off, I am pretty new to this kind of audio stuff. I have some basic knowledge of analog electronics and some basic skills such as soldering, but I am in need of some help troubleshooting what could be going on.

    I was given a Kenwood KR-4200 receiver and two KLH Model Seventeen speakers. I figured since they were free, I would at least put a little effort into seeing if I could get them going and sounding good, despite not knowing anything about audio equipment. As far as I can tell, these sat in a basement for a number of years and seem to be in good condition. The first problem was that one of the tweeters in one of the speakers wasn't working (I couldn't measure any resistance across it), so I bought a replacement one and it works. It sounds really good, except:

    The main thing seems to be that there is some source of noise coming from somewhere. Here are the characteristics of it: upon first starting the unit up and playing music for a few minutes, it is pretty minimal and everything sounds pretty great. After a few minutes, the hissing white noise grows a little louder, and continues to grow with time until it is quite noticeable (it doesn't take too long to get to this point, maybe 10 minutes). Switching the speakers to the other channel (i.e., so that it is on B instead of A) doesn't seem to help. The white noise does not increase with volume adjustment.

    Upon removing the top of the receiver, everything seems to look ok, if a little dusty. None of the components look visually to have reached a point of catastrophic failure, i.e. resistors aren't discolored, caps aren't leaking anything, etc. I do note that there are 4 transistors in a U shaped heatsink that get quite warm, perhaps these are the cause?

    I can provide pictures of the interior of the unit if that is helpful.

    Thank you in advance for those who respond and are willing to help!



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  2. mbz

    mbz Super Member

    Melbourne, Victoria
    Download service manual from hifiengine, need to register, it's safe.

    White noise coming from both speakers?
    Does noise increase with volume?

    Tone amp has Q11,12 as 2SC1000, these have a history of going noisy. I wouldn't replace yet.
    Buy a can of freeze spray and give Q11, 12 a squirt and note any effect.
  3. Watthour

    Watthour Electron Rancher - JS3600

    It appears to have some 2SC458s in the tuner board AF output and 2SC1345s in the main amp (differential pairs) which could be making plenty of noise.

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