01-29-2023, 06:22 PM
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.....
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.....
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
