Ruark Vita Audio R4 Mk3 will not power up- fixed

[rh100605]

My Ruark R4 mk3 suddenly refused to power on.

When I removed the back panel I was able to measure the power supply outputs with the mains power applied.

All voltages were near zero. I used an isolation transformer and then probed the output voltages with an oscilloscope. The standby voltage was pulsing around 500 mv.

The power supply board  consists of one bridge rectifier supplying 300V dc to two switched mode power supplies both with dual outputs.
The first supplies 8volt standby and 12 volts on the 6 pin connector (Pin 1: Gnd Gnd Vsb Vsb 12 V PSon )

It uses the Power forest PF6000AG sot23-6 IC marked 6000 which I bought on Aliexpress. Scribd has the first page of the datasheet.

The second supplies +/- 20 volts for the final audio power amplifiers and uses the LD7580 FGS Leadtrend 8 pin switching regulator which is enabled by voltage from the PF6000 chip.

I replaced the PF6000 chip to no avail and then checked all the diodes in circuit with a DVM for 0.2/0.3 forward voltage and large reverse resistance to eliminate shorted diodes .

I found D10 an Panjit MBR1200 diode ( 1amp 200V Schottky) nearly shorted and replaced it with an MBR 2200 ( 2amp 200Volt Schottky)

The whole power supply sprung into life and so did the radio.