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Kenwood ka-6004 problems/ right side scratchy low volume

Would like to speak to anyone that may be familar with this series of amp. I purchased this amp in 1972 new in Europe and has been sitting for a couple of years. Would like to talk to anyone about the major parts of this amp and where I should start if I need to recap it. Its been a few years since I have done any electronic work and never on stereos. A little guidance on this unit would be very much appreciated. It is very weak on the right side output, switching speaker leads switched the problem so I know that both speakers are good.

re: Kenwood ka-6004 problems/ right side scratchy low volume

Its a very simple thing. All the over 20year old electronics need a fresh (!) high quality electrolytic capacitors. Ageing electrolytics would burn transistors and diodes - and make it weak or dead one too. Even a power transformer would be hot or dead ! Same thing can also use a 0.5mm solder all over the board and cables too. That age Kenwood are very good made and keep it so.

re: Kenwood ka-6004 problems/ right side scratchy low volume


I assume that you have tested it with more than just one signal source (phono, tuner, aux). A weak channel can be in any part of the amplifier so we have to isolate the section responsible for the problem. First, I recommend that you download the KA-6004 schematic in the Library section ( https://www.hifiengine.com/manual_library/kenwood/ka-6004.shtml ) and study it a little, identifying the various sections and controls within the diagram against the real thing.

Now we can divide the amplifier into two major sections: preamplifier and power amplifier. To determine wich section is responsible for the problem is sufficient to use the Normal-Separate switch on he rear panel. Turn OFF the amplifier, move this switch to "Separate" position and inject an external signal source in the main amplifier input. However, CARE MUST BE EXERCISED to connect a source that have THEIR OWN output Volume control to avoid blowing out your speakers if the signal overloads the power section.

With the amplifier turned OFF, connect the source (tuner, cd player, etc.) with their own volume at the MINIMUM in the "Main In" RCA jacks of the KA-6004. Turn on the amplifier and slowly turn up the CD or Tuner volume. If both speakers plays equally loud, the problem is in the preamplifier. If not, the problem is in the power(main) amplifier section.

You mentioned the sound being "scratchy" with low volume and the amplifier being out of service for roughly two years.
Inactivity is bad for equipment of this age favoring contact oxidization, electrolytic capacitor failure and a host of other electronic problems. If you haven´t already made a general contact cleaning on pots and switches is a good idea to start doing it now, even as a measure of preventive maintenance. Use a commercial grade contact cleaning product of good quality and follow the instructions.

If "scratchy" means a high distortion level, this can be caused by various electronic problems. To find out what is wrong we must divide the section were the problem is in various stages or sub-sections and do some tests on each section.

If you have access to an audio generator and an oscilloscope and know how to use them, such a problem tends to be much easier to debug. However, if you only own a multimeter it is also possible to do it, only the search for the problem being much more involved.

Stereo equipment have a unique characteristic that is a great aid in troubleshooting: you can compare voltages, currents waveforms and signal amplitudes between channels (when only one is bad), and deduce, by comparison, what is wrong.

Hope this little guide can help you start debugging your Kenwood. Japanese stereo equipment of this vintage is generally of good build quality, simple and easy to correct any failures. Just a little knowledge and common sense is sufficient to preserve these equipment in good working order, giving years of trouble-free performance and satisfaction.