Korg Poly800/EX800 Users

On Thu, 2009-03-12 at 15:32 -0700, TheTravelSource Fes wrote:
> Is there a component that is likely the problem that is breaking the
> circuit when I plug in the A/C adapter? If so, can you give me the
> circuit board reference from the service manual below? (Thanks to
> whoever upload that!) Again, this is a first generation Poly-800.

Okay, look at page 6 of the service manual.

When you put a plug in the DC socket, the two "+" terminals are pushed
apart (the two V shapes in the diagram).  Thus, the power supply is
connected with the negative terminal to the thick black middle pin and
the positive terminal to the upper "V".

In both cases the positive supply goes through the on/off switch to the
rest of the PSU circuit.  The reverse-polarity protection diode D2 can't
be at fault, because if it was shorted it would short the batteries just
as happily as the PSU.

The negative terminal of the battery goes to the emitter of Q1,
bypassing it.  Q1 and friends form a simple voltage regulator, probably
set for around 9V.  Measuring across D1, you should see the voltage from
the power supply - around 9v, probably a bit more.  You should see about
9v across C3 too.  If not, then Q1 isn't conducting for some reason.
First thing to do is test Q1 and then see what the voltage is across D4
(the regulator zener diode).

Gordon