Without getting out my schematics and going into what you are doing, You should be aware that if you are using one of the JVC test discs, the older version has a defect. That disc is labeled with the number 4DE-202. I have one of these, it is the small disc that came with the demodulator. Not too long ago, I read of this defect and had remembered that I had made a note on the jacket many years ago about what I then perceived as a defect. I had noticed that the behaviour of the disc did not match what it should have been with a correctly working demod. I pulled the disc and this is what I had written on the jacket:
(At band 2) Right channel recorded wrong: adjust for low output on (right) rear channel
This notation matched what I had read that day. Of course, if you are using a different alignment disc, or are using the later version where this problem was corrected (I believe it was 4DE-203), this does not apply. You can still do the test by switching the input connections to the demod so that you are using the left channel test tones on band 1. Hope this helps.