No liquid damage or visible physical damage. Customer initially stated it suddenly no display.
All the diode measurements on the Backlight power circuity matches a good board.
All the diode measurements on the Backlight power circuity matches a good board.
- Replaced UP800 (backlight boost IC) twice, also reflowed
- Replaced DP800
- Replaced QP800 (backlight power switch MOSFET)
- Replaced UD050
- Tested with a known-good display – still no backlight
- No corrosion or mechanical damage on board
| Signal / Component | Voltage | Notes |
|---|---|---|
| FL800 (backlight fuse) | OK, passing | Fuse is intact |
| PPVIN_LCDBKLT_R | 12.0V | Input to UP800 |
| PPVIN_LCDBKLT_Q | 12.0V | Output of QP800 (after gate forced low) |
| PP5V_S2 | 5.18V | Present |
| PP3V3_S5 | 3.28V | Present |
| LCDBKLT_EN_L (QP800 gate) | 11.93V | Too high, not turning on QP800 |
| BKLT_SD | 11.93V | On good board, reads ~5.5V |
| BL_PWR_EN | 1.80V | Reaches UP800 pin 17 through RP842 |
| RP842 | 0Ω, 1.80V both sides | Confirmed good |
| LCDBKLT_FB (UP800 pin 2) | 12.0V | Too high, expected ~1.2V |
| LCDBKLT_SW (UP800 pin 1) | 0V | No switching activity |
| LP800 (inductor) | 12V | Receives power after QP800 forced on |
| Display | Known-good tested | Still no backlight |
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