Replacing things randomly in this unit will be frustrating and expensive since it is a complex device. The power supply needs to be checked to find if a rail is pulled down, a common cause of this symptom
There are supplies for +48, +/- 17, +/-8, +/-12, +3 and +5V. If you do not have all of these and clean, you need to find out why.
What test gear do you have available? Working with a switching power supply requires a little caution working with the secondary and a lot of caution in how you make your measurements on the AC input side.
This is a difficult unit to repair if your don't have a decent collection of test instruments.