we are onto something here----
i turned R17  trimpot  clockwise  about 45 degrees clockwise  and the led went on-- the control panel returned to normal Led patterns----  i went another 10 degrees and now when i start it up it flashes the  bulk of the Leds  once ,   and then stabilizes with the normal  ON pattern , and controls work and the unit plays normally (so it seems) . --  i then measured the voltage  as you described --it was maybe 4.8v    so i turned  R9 up till it neared 5v ,  then i was able to turn R17 down  some --
now  the same '10degrees past Led lighting up '   was an increase of only about 30 degrees of clockwise  rotation .  is there a 'balance between these trim pots?  can they be set too high?  or is it 'fine'.....

Does this mean the transformer or another part of the power supply system is damaged?  it seems like  a big adjustment since it was fine a half hour before and my other keyboard that was plugged in at the same time thru the same power strip   ( a DSI Polyevolver) seems to have has some  memory corruption that seems like some internal electronic damage and the factory tech guy has suggested i send it in to them for repairs.

thank you so much because this seems be solving the recent Polaris crisis-------