Hello, dear experts. Maybe I create this topic in wrong coference, but I don't know where could I aks about it. So, we have problems with a following mature product:

SIEMENS UPS B4208 / 16 puls rect.
TYPE: D400/115

Order No: 6SU4208-0AA00-1MA0

P = 80 KVA, 1993.

After switching off the UPS for battery maintenance the inverter doesn’t work. After switch on rectifier input switch-disconnector Q10 the red LED H4 lights up on the module A101 (see page 1 in the Attachement). After pressing the button Inverter On/Off and button Enter (Invertor On) a red error symbol lights up on the display. This error could be reset by the button S1 on the module A102. Simultaneously red LED H4 lights on the module A101 (see page 3 in the Attachement).

When we try to start the inverter again, red symbol of inverter’s error turns back on the display. After error reset (by the button S1 on module A102) red LEDs H1, H2, H3, H5, H6 light up on the module A101 instead of LED H4 (see page 2 in the Attachement).

See pictures of LEDs state and display symbols in attachment.

When we try to switch on the UPS, situation is repeating cyclically on the unit A101.

Please help us in determining of possible causes of error: either fault of module A102 or fault in inverter power circuit.

Module A102 is not available for us to replace the faulted one.

Thanks. Any your help will be appreciated.

Best regards, Alexander