Technics SU-X950 no bass?

[redrooster]

I found this old school hybrid chipamp at a recyclers,after I cleaned it up and turned it on I noticed that there was no bass on one channel,so I cleaned the volume and balance potentiometers with Deoxit and then there was no bass on either channel? I pulled the volume pot apart, it looked OK,the bass tone pot has six pins coming out of it? so I just gave it a spray of contact cleaner,I didn't disassemble it for a clean just in case I had trouble putting it back together again.Ive stripped the amp down and resoldered some pins on the main power chip that looked a bit dodgy other than that I cant find anything wrong, all the transistors, resistors and electrolytic caps seem OK. I have a service manual but this type of early digital amp is hard for me to understand where the problem is? Any ideas anyone?

 

[TLS Guy]

I found this old school hybrid chipamp at a recyclers,after I cleaned it up and turned it on I noticed that there was no bass on one channel,so I cleaned the volume and balance potentiometers with Deoxit and then there was no bass on either channel? I pulled the volume pot apart, it looked OK,the bass tone pot has six pins coming out of it? so I just gave it a spray of contact cleaner,I didn't disassemble it for a clean just in case I had trouble putting it back together again.Ive stripped the amp down and resoldered some pins on the main power chip that looked a bit dodgy other than that I cant find anything wrong, all the transistors, resistors and electrolytic caps seem OK. I have a service manual but this type of early digital amp is hard for me to understand where the problem is? Any ideas anyone?

What service equipment to you have? T.
his is not the sort of vault you will find without a signal generator and scope.

Most likely there is a bad DC isolating cap gone bad some place, but you will never guess where.

The procedure is to pass sine waves, in this case of low frequency, and look at the peak to peak voltage of the wave on the scope, comparing the two channels, and see which stage is acting as the low pass filter that should not be. By the way that is not a digital amp, but very much of the simple analog variety.

I guess you have found out why it was at the recycling center. If you do not have the requisite skill sets and test equipment, then you need to return it to the recycling center.