Today ran a short bench test on the Kenwood Trio KA-8006 integrated amp. The control pots on the amp were very dirty so to start I needed to clean them well to avoid the distortion they were creating. Once clean I noticed a very tell tale sign of something wrong. After five minutes of idling the output heat sink on the right side was cool to the touch whereas the left was getting warm. Checking for DC at the speaker terminals nothing on the right and 1.9mv on the left. Not horrible but any DC to the speaker terminals is not desired. On to the scope and a 1kHz output run.
The left channel will amplify and creates a stable waveform, however there is distortion which is possibly a noisy transistor in the amp section. It will run to 68w on a 8 ohm load at maximum volume and does not hard clip. Weak but not terrible. The right side has no output, no waveform seen and as you increase the volume you get a distorted flash of a sine wave. The right side has some major issues which will have to be dealt with. Hopefully, the outputs have not been damaged, but can be replaced with modern substitutions.
On close inspection of the power supply board there are some very noticeable burnt resistors. The caps next to the fried resistor appear to have some char on them as well. The power supply board may need a good overhaul first to bring the power rails up to spec since those components are obviously on their way out.
For its age the issues here are fairly normal. As with every restoration done, this amp will have a very good overhaul done. The electrolytics will need to be replaced and there are a few transistors that will be changed regardless of condition do to being failure prone. Once the power supply is in good working order then the right side can be diagnosed. Below is a shot of the power supply board in the area where a resistor has burnt up a bit. It does look worse then it actually is due to the PCB glue under the caps but still that resistor is definitely not in spec anymore. Next, it is on to parts ordering and then replacement pictures coming.