First of all, I'm new to this forum, and I'm happy to be accepted as a member.
I have gone through a Sony SQD 2020 restoration project and I thought it would be good to share my experience, also because I found
a few errors in the Service Documentation that is available at various places on line.
When my SQD 2020 came in it wasn't working properly at all: signals completely off balance in SQ mode and loud intermittent noises occurring at random moments.
After reading about this online, I soldered through all connections on the B-board (the large PCB with all the trim pots on it) where pins make connections between the top and the rear of the PCB. (There are many of them and make sure you don't miss one.) In my case this even turned out to be necessary to do this on both sides of the PCB. I also cleaned the SYSTEM switches. After this the SQD 2020 worked much better and the intermittent noises were gone.
In the SQ-mode, however, there were still problems. The channel separation was bad, and the rear speakers 'pumped': they sounded as if some kind of dynamic expander active.
I therefore decided to go through the calibration procedure as explained in the Service Manual.
On page 18 it is explained that you either need the SONY SQ CHECKER (which of course I didn't have) or build a Signal Mode Selector based on the
diagram in figure 3-1 on the same page.
However, after many unsuccessful attempts to calibrate my SQD, I came to the conclusion that
there is a serious mistake in that diagram!
Based on the attached files I will explain what this mistake is.
I analysed the main signals in the diagram (the ones that go to the switches and then to the input of the SQD 2020) as follows: in step 4 (left-back + right back) the phase relation between the left and the right signal should be 180º. Therefore, the blue signal must be 0º and the yellow signal must be 180º. In that way, step 1–4 are like this:
Step 1: 0º on left channel, nothing on right channel
Step 2: nothing on left channel, 180º on right channel (why this is 180º is a mystery to me, but since there is no signal on the right channel it doesn't make a difference)
Step 3: 0º on both channels
Step 4: 0º on right channel, 180º on right channel
At position 5 of the switch (left-back), the phase relation between left and right should be 90º, so since the 0º (blue) is connected to 5 at the left channel, the signal at 5 on the right channel must be the 90º phase (yellow).
Then at position 6 (right-back), the phase relation should be -90º. However, looking at the diagram, the 90º signal is connected to the left channel, and the 180º signal to the right channel.
The resulting phase relation is then +90º, and not -90º as it should be.
This explains why Sergeauckland wrote that "The Tester works OK, (mostly) but has a very peculiar response on Rb".
I corrected the diagram in the next image, so that in step 6, the 180º signal goes to the left channel and the 90º goes to the right, resulting in a phase relation of -90º.
In this way the Signal Mode Selector works correctly throughout the whole calibration procedure.
Something else that I would like to mention regarding the Service Manual, is that on page 22, it says that measurements should be made by touching the collector of several transistors on the B-board. This is actually not necessary at all, since at least in my SQD 2020, there are measuring points on the PCB next or close to the transistors Q811, Q804, Q815, Q817 and Q910. This makes measuring the currents at these points much easier.
Then on page 23, there are
two more mistakes!
At point 4 of the procedure under 3-11,
RV801 and RV802 are swapped. While measuring the level at
Q811,
RV802 should be adjusted, and while measuring
Q815,
RV801 should be adjusted.
A similar mistake can be found at points 2 and 3 of 3–12. At
point 2, RV907 should be adjusted, whereas at
point 3, it should be
RV906.
After having gone through the whole procedure, my SQD 2020 works wonderfully!
I hope this was helpful.
