zetafunction wrote:I just checked this circuit and there is a problem there. There is no voltage across C845 present! The voltage enters with about 12 V the connector and gets to TR310. Between the drain of TR310 and the connector ground are still 12V.
Is it possible, that T302 is the problem?
i suppose the transformer could be bad, but more likely something in the chopper driver and feedback circuit. i'm going to paste this as reference from a post on page 8:
There is a DC supply voltage coming from the Top Board across the CN1 connector on pins 5-8, with ground on 1-4 and 47-50. This is filtered by an electrolytic cap, C841, 15uF 35V, and is then chopped thru a transistor TR310, an N-FET 2SK3484 100V 16A, to excite the PRIMARY on pins 8-9 of the CV transformer, T302. The gate is driven by a 10W flyback switching regulator chip, IC702 JRC 2369Z.
There is a First Secondary on T302 pins 6-7 that is half-waved thru diode D334, 2U 1D, that ties back to the CN1 supply ground and regulated by IC317, M050 5V regulator. This 5vdc is used for the supply voltage on two isolation amplifiers, PC312, 313, Broadcom A 7827. PC313 is sending the output current sensed thru R232, 0.008 Ohms, across the isolation slot to an op amp, and then on to the CN1 connector back to the top board. PC312 is sensing the  HV output voltage and sending it back up to the top board on CN1, pin 42. So the box is smart enough to measure itself and likely won't come on if something doesn't feed back properly to the top board.
There is a Second secondary winding on pins 2-3 that is half-waved thru D328 2U 1D, filtered by C367 10uF 25V, regulated thru IC314, M050, that creates another 5vdc routed to IC301, etched part number ?277?.
And there is a Third secondary winding on pins 2-4 is half-waved thru D331, filtered by C 845 15uF 35V, that provides ~ 16.6 vdc supply voltage for the PFC chip, IC312 UC2854 and to the solder pad pin “13”, which is the positive rail of the push-pull gate driver for the 3 PFC gates. There appears to be an adjustable shunt regulator at IC318, marked TACQ, TI TL431-Q1, that provides a feedback signal back to the flyback regulator chip, IC702, that is pulsing the transformer. The 16.6 was my calculated value based upon the resistor network for the shunt regulator.
The ground reference for the 2nd and 3rd secondaries is to solder pad “11”.
ic702 is located on the bottom side at the edge covered by the waffle plate, but it sends the gate drive signal to the TR301 FET based upon feedback from ic 318 (very tiny and located near PC301) to excite the PRIMARY winding of TR302.
If it is not working properly then the 3 Secondaries will not be energized and you would not get any of these low voltage dc supplies. i.e.. the rail for the PFC push-pull, and the current sense 5V supply.
i would first probe to check anything you can reach such resistors, chip capacitors, diodes, etc.
Does TR301 have a body diode internally, that could be checked.
There is a 330 Ohm resistor from pin 4 of ic702 to the gate of TR301. It has test point solder blobs on each end that you might be able to reach. Maybe it is open circuit?