5 volts only for ST motherboard?

[Darklord]

Okay, I know this can be done. In fact, I did it years ago with my STacy by using a
Pico P/S to send +5 into a line on the 2nd floppy drive wiring harness that the
STacy has. It powered up fine. I wound up not using it because I couldn't figure
out a way at that time to feed -20v to the original LCD screen.

Fast forward - I've got a handful of people telling me on Facebook that you can't
use just +5 volts alone. I already know that you have to provide a -12 volts to get
the serial port to work.

They are saying that without +12v fed into the ST's motherboard, you get no sound.

None. Nada. Zilch.

I honestly don't remember checking for sound back when I was experimenting with
+5v because I was concentrating so hard on getting the original LCD going.

So...does anyone know for sure if that's right or not?

Thanks much - just really curious. :)

[rubber_jonnie]

Pretty sure that the Ym2149 only needs 5v and I know 100% that STs will run off only 5v, you just need 12v for serial AFAIK.

[frank.lukas]

The driver transistor that drives the sound output need +12V, so with only +5V there is no sound via the monitor output. The RF modulator for the TV output need also +12V ...

[Darklord]

Okay, thanks.