If you are troubleshooting a "No Power" or "No Display" issue, these are the standard voltages to verify on the LA-C391P: Main adapter voltage (Check entrance MOSFETs). +3VALW / +5VALW: Always-on voltages generated by the standby IC (TPS51225R). +1.35VPDDR: RAM power (DDR3L). +1.0V_ALW: PCH core power. +VCC_CORE:
If your APW70 LA-C391P has stable always-on rails but refuses to boot, you must trace the startup handshake using an oscilloscope or multimeter. Look for these critical signals on the schematic:
The APW70 is a motherboard manufactured by Compal Electronics, primarily used in high-performance portable workstations and rugged devices. This specific board model is most commonly found in the HP ZBook 17 G3 Mobile Workstation .
However, I can suggest some possible sources where you may be able to find more information: apw70 lac391p schematic portable
Enables tracing signals between the APW70 , KBC, and CPU. 5. Tips for Portable Repairers
Ensure input voltage is present.
| Symptom | Likely cause | Schematic section to check | |---------|--------------|----------------------------| | No power, no LED | Input fuse, blown MOSFET | Primary side of APW70 | | Flickering LCD | Bad capacitor on output rail | Secondary caps (1000µF/16V common) | | Dim display | Backlight inverter failure | Transformer or CCFL driver | | Touch works, no image | LVDS cable or TCON power | 3.3V & 1.8V rails to LCD | | Intermittent shutdown | Overheating regulator | APW70 feedback resistors | If you are troubleshooting a "No Power" or
The primary isolation MOSFETs near the DC-in jack take the brunt of power surges. If they fail open, 20V will stop right at the gateway, preventing the B+ rail from forming. Check the gate voltage driven by the charging controller to ensure the chip is actively trying to turn these transistors on. Blown Backlight Fuse ( F1 / F2 )
Located under the MXM slot area; frequently queried during motherboard repairs for GPU power delivery issues.
To assist you further with this motherboard repair, could you share what the laptop is currently exhibiting (e.g., completely dead, looping power, or no display)? Additionally, letting me know what diagnostic tools you have on hand (like a multimeter, oscilloscope, or bench power supply) will help tailor the next troubleshooting steps. Share public link This specific board model is most commonly found
The number “APW70 LA-C391P” is often confused with a specific integrated circuit, but it is the and Compal Board Number (LA-C391P) for the motherboard used in the HP ZBook 17 G3.
Essential for finding the exact physical location of components labeled on the schematic (e.g., PL, PQ, PR, PC).
The output voltage is fed back to the to maintain a stable output voltage (e.g., 1.0V1.0 cap V for CPU/GPU). D. LAC391P Monitoring
| Source | Search term | Likely result | |--------|-------------|----------------| | (ex-HP/Agilent) website | LAC391P service manual | May have PDF under "obsolete products" | | Artek Media (manual seller) | APW70 schematic | High-quality scan of original | | ElektroTanya (free) | HP APW70 diagram | User-uploaded service manual | | KO4BB (HP/Agilent archive) | LAC391P | Large collection of old HP service docs |