Before proceeding with power supply troubleshooting, check

• presence of proper A/C at the power cord.
• proper voltage tumbler setting.
• two receptacle fuses [disconnect power cord].

Input power is split right after the EMI filter. One line goes to the cooling fan, the other feeds the transformer primaries.

The power supply transformer assembly contains discrete components. Early diagnosis of a failed power supply may indicate a failed assembly. Continued diagnosis will lead to failure of a discrete component. The FRU you replace (assembly vs component) depends on your individual repair situation.