General Assist Technical Reference
LATT 3 Phase Power Factor Correction (PFC) Board Check
PFC board supply path, DC conversion and common fault indicators
The LATT 3 Phase Power Factor Correction board receives a three-phase supply through the filter board and converts the incoming AC supply to a DC output for the inverter circuit.
High-voltage circuit: The PFC board operates with 415 V AC three-phase input and approximately 560 V DC output. Testing must only be carried out by appropriately qualified service personnel.
1. Three-phase supply path
| Phase | Wire colour | Supply route |
|---|---|---|
| L1 | Red | Filter board to choke coil reactors |
| L2 | White | Filter board to choke coil reactors |
| L3 | Black | Filter board to choke coil reactors |
Supply overview: The PFC board is supplied with all three phases via the filter board. The red L1, white L2 and black L3 conductors then connect to the choke coil reactors.
2. AC to DC conversion
The diode bridge converts the three-phase 415 V AC supply to approximately 560 V DC. The DC output is measured between the positive (+) and N terminals.
3. Diode bridge check
A diode test can be carried out across the diode chip. The board provides three active phase inputs together with positive and negative DC output connections.
| Connection group | Function |
|---|---|
| Three active phase inputs | Incoming three-phase AC supply to the diode bridge |
| Positive DC output | Positive side of the rectified DC output |
| Negative DC output | Negative side of the rectified DC output |
Important: The source material identifies the diode test points and connection groups but does not specify expected diode-test meter readings. Refer to the applicable service procedure for model-specific test values.
4. Common PFC-related faults
| Condition | Service relevance |
|---|---|
| AC overcurrent | Listed as a common PFC board fault condition. |
| Low voltage | Listed as a common PFC board fault condition. |
| DC voltage too high | Listed as a common PFC board fault condition. |
| Missing supply phase | A PFC error will be generated if one phase of the supply is missing. |
Key diagnostic point: If a PFC error is present, confirm that all three incoming supply phases are available before progressing further with board diagnosis.
General Assist Technical Reference