Hello everyone, I'm looking for help to diagnose a Harman Kardon 430 from 1976-78 and how to fix it. It is a twin powered receiver which outputs 25 watts per channel into 8Ω.
Here is the service manual : http://akdatabase.com/AKview/albums/userpics/10004/Harman Kardon 430 Service.pdf
The unit is powering up and all of the lamps are working. I have tested it using the AUX input and the tuner. In both cases, the problem stays the same : sound is coming from the speakers, but at a ridiculously low level. I had to set the volume control around 2 o'clock for the sound to be audible.
My guess is that the problem is either on the Main amp board, or on the Rectifier C board which powers the Main amp, or both. Another thing to consider is that since the unit is twin powered (one for each channel), the same problem must have occured somewhere on the signal path on both channels. However no luck finding obvious causes so far...
So far I have used a vacuum cleaner for removing dust and have ordered air duster and deoxit. I have checked all the fuses (I found 7), and all of them seem to be working. I have also checked for blown resistance and didn't find any. Some parts of the board seem to be corroded (or burned?), I'm not sure how this affects the functionment.
I'm also unsure if some caps are bad or just glued to the board (first two pictures) or glued together (last four pictures).
I have a multimeter, but unfortunately no oscilloscope. I have also ordered a soldering iron so will be able to take out componants to test them.
What do you think may cause this?
Thanks for your answers.
Here is the service manual : http://akdatabase.com/AKview/albums/userpics/10004/Harman Kardon 430 Service.pdf
The unit is powering up and all of the lamps are working. I have tested it using the AUX input and the tuner. In both cases, the problem stays the same : sound is coming from the speakers, but at a ridiculously low level. I had to set the volume control around 2 o'clock for the sound to be audible.
My guess is that the problem is either on the Main amp board, or on the Rectifier C board which powers the Main amp, or both. Another thing to consider is that since the unit is twin powered (one for each channel), the same problem must have occured somewhere on the signal path on both channels. However no luck finding obvious causes so far...
So far I have used a vacuum cleaner for removing dust and have ordered air duster and deoxit. I have checked all the fuses (I found 7), and all of them seem to be working. I have also checked for blown resistance and didn't find any. Some parts of the board seem to be corroded (or burned?), I'm not sure how this affects the functionment.
I'm also unsure if some caps are bad or just glued to the board (first two pictures) or glued together (last four pictures).
I have a multimeter, but unfortunately no oscilloscope. I have also ordered a soldering iron so will be able to take out componants to test them.
What do you think may cause this?
Thanks for your answers.
