Troubleshooting a KA-8300

I have a KA-8300 standing around for many years now. I got it from somebody (with the working tuner ) because it was 'broken'.
Intending to repair it, this afternoon, I checked it out to see what is the problem.
First, when I switched it on and the relay clicked, the sound was good, however, after about 20 seconds, popping sounds appeared on one channel.
I tried to isolate the problem by playing with the settings and nothing changes the poppint, it remains there and the volume control does not affect it (it appears as superimposed on the sound).

I checked the next:
- pre/ main switch
- volume control
- balance control
- mono/stereo switch
- all tone controls
- input switch
- speakers switch

I think this isolates the problem to one of the components on the power amplifier PCB, or is this possible a result of a bad ground somewhere?
Does any of you guys have a hint on what component might be responsible?
Otherwise, I just replace everything on the power amplifier that I can easily get my hands on.
I'm already happy that the TA-100W's are OK.

another step would be to seperate the pre-amp & amp with the switch and cross connect the pre-out and amp in .. L to R etc. this will tell you if the pre-amp has the problem or the output amp board.
if you rebuild the amp board I would do both of em. Caps and xistors and any other replacements you want to do. (diode/s etc) Usually it's a transistor breakdown or a cap going bad that I've found. Could be something else also.
My .02

John M

The good aspect of this is that there are not so many components involved.
I will try to source the components and keep you guys informed.

In this amp there is a pair of PNP transistors (Qe1 and Qe2, 2SA750) at the input, in a differential stage configuration. The problem that you have is often associated with mismatched transistors in the differential stage. Did you measured the hFE of these transistors in the defective channel?

I have not yet pulled any components.
I have made a list of the components (for one amp, as I need it twice):

Capacitors:

1 muF 50V
47 muF 63V
33 muF 10V
330 muF 6.3V
47 muF 6.3V
1 muF 63V

Semiconductors

2SA750 (1) (E) or (F) (2X) => 2SA970BL discussion
2SC1628 (O) or (Y) or 2SC1885 (R) or (S) => 2SC2911
2SA818 (O) or (Y) or 2SA912 (R) or (S) => 2SA1209 discussion
Zener Yz-140 => 14V 500 mW discussion
1S2076 (2X) => 1n4148

I intend to first replace the capacitors and then do the semiconductors with sufficient intermediate testing. Since the 2SA750 need to be matched, I can leave them for the last and first redo the other components (and hope the problem is not with them). I currently do not own the equipment to measure the hfe of a transistor although I can make one if needed.
I can of course always try the pair from the other side.

In the mean time, I have sourced the components. Replacing the caps did not appear to solve the problem. So I turned myself to the semiconductors.
Replacing the 2SA912 / 2SC1885 pair with a 2SA1209 / 2SC2911 pair solved the problem.
I decided no to touch the 2SA750 pairs as they seem OK and I have read stuff about pairing.

Later tonight, I will clean the controls and put some new lights in the meters. I'm a happy man!

good to hear that .. it's a very good integrated..

Even with extensive contacta, the controls are still kind of scratchy. My other KA-8300 has the same issue and I have read a comment of EW that this is a general issue on this generation Kenwood. Is there a trick to resolving this issue?

Besides that, initially (with the new caps), the amp sounded very bass heavy, after a few hours, it seems to have settled and sounds very detailed.

Best plan of action is to clean the controls as well as you can, and simply use the thing.

I've had really good luck with finicky controls by cleaning with DeOxit D-5, working the controls, waiting about 2 hours, then repeat. Wait two more hours, and follow up with DeOxit Gold.

Thanks for the hint, I find it interesting that this one has 6 pots instead of the usual 4.
I will keep on trying with deoxit.

I second that...
same here with the DeOxit Gold ... or the old fader lube as it was called ..