[morzh]

Today I decided that I had in fact left one stone unturned, which is to check the driver itself, and opened up the patient again.

I decided to take a good look at the driver. I noticed that

1. There is a mistake in the sch (one of the diodes shown backwards).
2. Instead of -6V there is -5V. This lowers the driving voltage by 1V. However, upon the investigation (I actually took the board out to recreate the circuitry), I noticed the LDO that creates the -6V out of -18V, which is supposed to be UA7906, is actually MC7905, which is neg. 5V LDO. The LDO seems to be factory installed so I do not think this was a repair. Also it connects to -10V instead of -18V (which is OK).

So, I am not sure I want to change this, as i am not sure if this was the factory practice for a long time. Whatever it is, it is factory. I could possibly get an MC7906 and out it instead, but as said before.....