Was on a mission to recap this unit. Started with the tuner/main assembly board. Unfortunately I didn't do a performance baseline before starting. After the recap I went to test and found that when listening to the radio, in stereo mode, the levels were very uneven. Much louder on the left channel then the right.

I confirmed this ONLY happens with the radio in stereo mode. The levels are even in mono mode. Other input sources work fine in stereo mode (phono, aux, tape 1&2) and it's obviously not a problem with the volume or balance pots etc.. It seems clearly something in the FM circuit.

The stereo light is on, the tuning strength very strong, the tuning indicator dead center and it's getting tons of stations in, just not evenly decoded to stereo.

Now I'm not sure if happened as a result of the caps changes or was there all along, since I didn't do that initial baseline. I have the service manual https://drive.google.com/open?id=0B_Yuh1ijNVjmMlJSQnlwNHNsSTQ but unfortunately no oscilloscope or MPX generator etc. It seems from the manual VR4 pot can adjust some balance between channels in MPX decoding and when I do make major alteration to VR4 portions of stereo signal balances and gets MUCH louder, but that realy only seems to bring up the "background" music of the station (e.g. lijke guitar levels etc ) and the vocal level get buried and the audio as a whole sounds more like in a cavern when doing that, so I don't really believe that is a fix of any kind. I've returned that to it's original marked position, of course.

Thoughts of what could be affecting the uneven levels? A particular part failure/drift?

 

Using an audio tester, the problem seems to be centered around HA 1196. See pic

Pin voltages captured
Pin #
1 13.3
2 3.1
3 8.3
4 10.5
5 10.5
6 5.8
7 6.0
8 0
9 0.9
10 2.5
11 2.5
12 0
13 2.5
14 2.5
15 2.5
16 3.3

The audio output on pins 6 & 7 are uneven. The voltages are slightly different there too. I believe the source input is pin 2. there is a lot of audio, various levels, on many of the other pins as well, though I'm not sure what they are are for in this circuit. This seems to be the demultiplexer circuit (best guess, given mono source in, stereo out).

 

Here is the datasheet for the Ha1196, outputs on pins 4,5 and feedback pins 6,7 it may need the 47K resistors or 510pF capacitors replacing.


https://www.google.co.uk/url?sa=t&s...ggaMAA&usg=AFQjCNH-h4ekuVGbwdhtdsbXnerHRyoUIQ