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Troubleshoot great old Kenwood home stereo power amplifier.

Discussion in 'General Electronics Discussion' started by lipsk1, Jun 1, 2020.

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  1. lipsk1


    Jun 1, 2020
    I have a home stereo power amp Kenwood Basic M1D. I am having trouble with it working fine and then cutting out. I have checked every variable i can think of, including power source, testing different speakers and making sure the speaker wire is the right gauge and equal length, testing the speaker wire terminal ports (A vs B), changing the fuse, searching for miscolored resistors, and checking for overheating and good ventilation. It just really confuses me because it will work fine all day and then the next day it suddenly it will click off with a pop in the speakers and the "protection light" starts blinking. I have a little background with electronics but this is beyond me. Can anyone please Help??
  2. Martaine2005


    May 12, 2015
    You certainly have done a fine job so far.
    I would start by looking very closely for dry/cracked solder joints all over the board. Use a magnifying glass, follow traces and put a little finger pressure on components as you go round the board. Be methodical. Try this first and let us know your findings.

  3. lipsk1


    Jun 1, 2020
    Thanks so much! I certainly will let you know...
  4. lipsk1


    Jun 1, 2020
    Just one thing..Does that possibility align with the fact that it would work fine for full day and then crap out the next??? Just making sure cause I work pretty slow lol. Thanks again.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    A cold (bad) solder joint may make good contact one day and the next day, depending on temperature and humidity and possibly a light knock to the amplifier's case the same solder joint may be open.
  6. Ylli


    Jun 19, 2018
    The protection circuit will trip if:
    1. Either the left or right speaker output offset rises above about 0.5 volts
    2. An over current is detected in the output circuitry of either the left or right channel
    3. There is a fault in the protection circuitry itself

    How deep do you want to dig?

    First thing I would suggest is to put a voltmeter across one of the speaker outputs and note the DC voltage when it is working. And watch to see what it is just before it cuts off. Then do the same on the other channel.

    Beyond that the covers would need to come off and some testing would have to be done inside.
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