V-Series Cassette Transmission Error - Main PCB Q2 Burnout
Applies To
| Primary affected product | V-series cassette models |
| Reported symptom | Transmission error |
| Physical evidence | Heat damage on the main PCB |
Failure Analysis
Inspection of the sample PCB found that the Q2 transistor on the switching power circuit had burnt out.
Additional components within the switching power circuit were also found damaged.
Suspected Root Cause
FGL identified that the operating temperature of the R5 resistor could rise above its original design derating limit under certain conditions.
As the resistor temperature increased, its resistance could fall more than expected, allowing increased current to flow. This increased electrical stress could then damage components in the switching power circuit, including Q2.
Why Cassette Models Were More Susceptible
On the cassette model, the PCB is installed facing downward. This arrangement can allow heat to become trapped around the PCB.
The investigation identified a higher-temperature condition when:
- The affected indoor unit was stopped; and
- The VRF system continued operating in heating mode.
| R5 Temperature Reference | Temperature |
|---|---|
| R5 design derating value | 97.5°C |
| Actual measured value - indoor unit stopped, system heating | 105.4°C |
Production Change
Due to procurement changes, the R5 resistor manufacturer was changed from Rome to YAMAKA Electric from August 2011.
The YAMAKA R5 resistor had a derating specification approximately 15 K higher than the previous Rome component.
FGL tested an actual unit fitted with the YAMAKA R5 resistor and the problem did not occur.
PCB Replacement Guidance
The PCB manufacture date can be confirmed from the date label fitted to the PCB.
Example: A PCB label showing 061130 indicates a manufacture date of 30 November 2006.
Warranty / Cost Conditions in Original Report
The original quality report stated that FGL would cover the PCB parts cost only where all of the following conditions were met:
- The problem occurred within 10 years of the installation date.
- The burnout point was confirmed at Q2.
- The sales area was FG AUST, FG EURO or FGEF.
Affected PCB / Spare Part References
| Series | Part Number | PCB Rating / Code | Applicable Product |
|---|---|---|---|
| V-series cassette | 9707514025 | K01FZ-0411HSE-C1 | AU□A20/25/30LATF |
| 9707514032 | K01FZ-0412HSE-C1 | AU□A36/45/54LATF | |
| S-series cassette | 9705027084 | EZ-0020PHSE-C | AU□20/25/30TFCMF |
| 9705027091 | EZ-0020THSE-C | AU□36/45/54TFCMF | |
| J-series cassette | 9705491076 | K01FZ-0402HSE-C1 | AU□20/25/30UFARR |
| 9705491083 | K01FZ-0403HSE-C1 | AU□36/45/54UFASR |
Product Action
| Product Status | Action |
|---|---|
| Already installed | Address if the problem occurs. For PCB replacement, use a spare PCB manufactured after August 2011. |
| Stock product | No action specified. FGL considered the number of stock units containing the earlier Rome R5 resistor to be small. |
| Current manufacture | Production countermeasure already implemented. |
Service Guidance
- For a transmission error on an affected cassette model, inspect the main PCB for signs of heat damage.
- Pay particular attention to the Q2 transistor and components in the switching power circuit.
- If Q2 burnout is confirmed, check the PCB manufacture date before fitting a replacement.
- Use a replacement PCB manufactured after August 2011 where applicable.
- Record the model, serial number, PCB part number, PCB manufacture date and exact burnout location when escalating.