PLEASE! Kenwood help!

[mjarve]

Again, with the Kenwood! This is a very strange receiver to me indeed! I am working on a Kenwood KR-3400 reciever (trying to repair/restore it). The original problem was very weak and distored sound, and I suspected bad amplifier outputs. This uses some custom KA-40W ICs made by Kenwood and I cannot find them any more and I was thinking of replacing the original amp with a gainclone.

As I was beginning to remove the power amp board (heedless of the fact that it was still plugged in and turned on!) I removed a connector, and “ta-da!” it works! Indeed it works fine, aside from an inordinate amount of hum; loud and powerful for 16WPC! But this is not acceptable.

The wire I disconnected goes from the power amp board to the pre-amp/speaker selector board. It has one blue and one orange conductor and where it goes on the pre-amp/speaker selector board it is marked “NF” (negative feedback?). With this cable disconnected it works fine as can be. But once I connect it again, the sound is weak and distorted.

What is this “NF” connection, and if the receiver seems to work otherwise without it, am I asking for trouble leaving it disconnected?

Again, this is a design I am simply not familiar with, and am a bit out of my league. Please help this young pup out!

[Konrad]

What is this “NF” connection, and if the receiver seems to work otherwise without it, am I asking for trouble leaving it disconnected?

"NF" negative feedback.
So it kind of works without feedback, then open loop gain is "distorted" ?
Or : in the negative feedback path there is usually a DC-roll off cap. if this cap or it's series resistor is broken you will have full feedback, and most probably the amp will most probably oscillate. Dont leave it like this for longer periods, as it is not designed for!
Repear it !

R