A 7.0-ohm resistor (rated for at least 150 watts) is necessary to simulate operational load during capacity checks. Procurement and Service Literature PS-850/PS-855 Component Manual | PDF - Scribd
If the unit is removed for storage, the battery must be maintained according to specific outgassing and temperature protocols to prevent degradation. Where to Source These Documents You can obtain official copies from these sources: ps-855b maintenance manual
This is classic capacitor aging. The manual lists C5, C6, C7 (typically 4700µF/50V) as primary suspects. It also provides instructions for reforming old capacitors using a variac if immediate replacement is impossible. or Artesyn). Check these sources:
Most PS-855B units are rebranded by major industrial OEMs (e.g., TDK-Lambda, Mean Well, or Artesyn). Check these sources: ps-855b maintenance manual