Service manual

Edition 101222
-- 31 -- s1Cad160
General failure of the power block
Failure in the power block frequently means the short--circuit of the DC bus. Unfortunately it
causes an avalanche of further failures. Mechanism of the avalanche of failures is shown on
the picture. DC bus short--circuit causes damage and disconnection of the shunt resistor
inside the module. Consequently resistors R125, R151 on the control PCB are damaged
into the disconnection. It leads to further failures, in particular of the PFC control circuit.
To avoid the damage of the control circuit the protective fuse and transient suppressor were
implemented. However it does not guarantee 100% of the control PCB protection.
WARNING!
When the power PCB is replaced, only the fully functional control PCB could be applied.
Verify the control PCB by checking the resistance of R125 and R151 on the CN1 connector.
Both resistors should have 10 Ohm resistance.
To check the power block measure the DC--bus voltage and/or check the PCB using
ohmmeter. The DC bus must be completely discharged before using the ohmmeter. Use
diode check mode. Presence of the big capacitor is showed by the growing resistance.