The fault can be further down the secondary output lines which are in the main board. If you had measured all the components in the power supply section and could not find the defective component, then try troubleshoot components beyond the power supply section. A shorted small ceramic capacitor in the main board can cause the whole power supply to malfunction.
True case study- A Samtron Monitor 4Bn sent for repair with the complaint of no power. After troubleshooting the smps section for sometime, I’ve concluded that the power supply is working and suspect something shorted after the secondary output diodes and this made me to trace beyond the power supply unit. By using the explanation above, I managed to traced and found a shorted small resin ceramic capacitor located at the 80 volt line in the Monitor color board. The capacitor shorted to ground and made the power supply to stop operating.
The value of the shorted capacitor was .22 microfarad 100 volt. Replacing only the small capacitor brought the power supply back to life again. In smps repair, we as an electronic
repairer must know how to distinguish as which section is giving problem. Spending and concentrating your whole time to check on a working section is just a waste of time, you should only concentrate on section that have problems so that you could locate the fault and make the equipment work again.