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.
Ka-8006
Nice Operation with the updates and commrntary
Original owner of the very same amp KA-8006 that I love. It died on me. No click sound on turn-on. Very hot green color resistors. The unit is clean inside, no dust etc. I’m an seniour ex computer programmer and PC technician, but I know nothing about PCB level electronics troubleshooting and repairs. I have the schematics and I need help to get my baby back to life. Thanks!!
Hi Stacy, which board are the resistors on that are hot? Might be able to point you in the right direction.
The hot green color resistors are on the top of the power supply card (see attacher image of similar issue on another KA-8006). The card is positioned behind the front pannel. I hope you can see the images on the following two links. Thanks! https://hudsonvalleyhifi.com/wp-content/uploads/2012/07/20120705-101138.jpg https://hudsonvalleyhifi.com/wp-content/uploads/2012/07/20120707-230952.jpg
Stacy, you have a short in one of your channels that is drawing high amounts of current and frying the resistor. A dim bulb tester at the least is going to be important to use on the amp during repair. I would start by pulling the outputs and drivers for testing. If you have shorted transistors a wholesale recap is not a bad idea. This amp is not the easiest to work on due to the position of the boards but well worth it. If you need help in repair shoot me an email mike@hudsonvalleyhifi.com