General Assist Technical Reference
LATL Outdoor Unit Upgrade
Controller PCB rework, TR PCB thermal interface refresh and ROM update
Field procedure for LATL outdoor units requiring the controller/TR PCB rework and software update
This procedure upgrades/reworks LATL outdoor units by relocating the high-voltage lead on the controller PCB, renewing the thermal interface on the TR PCB, and updating the outdoor control software using a ROM writer.
Electrical safety: Isolate mains power, apply lock-out/tag-out controls and allow the DC bus to fully discharge before touching any PCB or connector. Use appropriate ESD precautions when handling electronic components.
Applies to
- LATL outdoor units requiring the controller PCB / TR PCB rework and ROM software update.
Tools and materials
| Item | Purpose |
|---|---|
| Phillips screwdriver set | Panel and PCB removal/refit. |
| ROM writer | FM-ONE or equivalent loaded with the required LATL program. |
| Thermal paste | Renew thermal interface on the TR PCB power device. |
| Alcohol wipes | Clean heat-sink/contact surfaces before applying new thermal paste. |
| Cable ties / side cutters | Secure the rerouted high-voltage harness in the required position. |
Upgrade procedure
| 1 | Access the control compartment Remove the front covers to expose the electrical panel and controller. Confirm the unit is isolated before proceeding. |
| 2 | Remove the TR PCB and renew the thermal interface Label and disconnect all TR PCB harnesses, then remove the TR PCB. Clean the heat-sink/contact area and apply a thin, even layer of fresh thermal paste to the power device. Refit the PCB and reconnect all harnesses. |
| 3 | Reroute the high-voltage lead Unplug the high-voltage (HV) connector from the controller PCB. Reroute the HV cable across the top edge of the PCB as shown in the source guide. Fit the ferrite and secure the harness with cable ties in the nominated positions to maintain clearance and minimise electrical noise coupling. |
| 4 | Connect the ROM writer With power OFF and the DC bus discharged, connect the ROM writer lead to CN5 on the main PCB. Restore power to the outdoor unit so the ROM writer powers up. |
| 5 | Select the required software On the ROM writer, select folder 212C_A71. If another folder is displayed, use the up/down controls to select 212C_A71, then press WRITE/OK. |
| 6 | Execute the software write When prompted to execute, select YES and press WRITE/OK. Wait while the programming process runs. |
| 7 | Confirm completion When Complete is displayed and the ROM writer asks whether to execute again, select NO and press WRITE/OK. |
| 8 | Finalise and test Isolate power and allow the DC bus to discharge. Disconnect the ROM writer from CN5. Restore power and verify normal operation, including cooling/heating start, fan operation and error-free status. Refit all covers. |
Important: Do not over-apply thermal paste. Use only enough to create a thin, continuous interface film. Keep the rerouted HV harness clear of inductors and heat-sinks in accordance with the source guide.
Acceptance checklist - attach to job card
| Done | Check |
|---|---|
| ☐ | Covers removed and reinstalled without damage. |
| ☐ | TR PCB thermal paste renewed and PCB correctly re-seated. |
| ☐ | HV lead rerouted, ferrite installed and cable ties secured in the required positions. |
| ☐ | ROM writer connected to CN5; program 212C_A71 written and completion confirmed. |
| ☐ | Unit power-cycled and operating normally with no active error codes. |
| ☐ | Photos taken of the reroute and ROM writer completion screen, where required. |
Service notes
- If the ROM writer does not power up, recheck outdoor supply and the seating of the CN5 connection.
- Confirm all labelled harnesses are reconnected to their original positions before restoring power.
- Record the software folder written and final operational test result on the job card for traceability.
Source: LATL Upgrade - Quick Process Guide (photo steps pp. 1-12)