Philips TV Red light bliking once, won't turn on.

The TV is not working, and the PSU (Power Supply Unit) appears to be the suspected problem. The PSU is not delivering the correct voltages for proper operation. We are investigating whether the issue lies within the PSU, the mainboard, or other components.

TV: Philips 55PUS7803/12

1. Measured Standby Voltage:
   • The TV should have a standby voltage of 3.3V to 5V.
   • The PSU instead delivers 7.4V on the standby line, which is too high. This suggests a possible fault in the PSU's voltage regulation circuit.
2. Forced PSU Activation:
   • We manually connected the PS_ON (ON/OFF) pin to GND to simulate a power-on signal and activate the PSU.
   • Despite forcing the PSU on, there were no changes in the output voltages. The +VM output remained at 8.43V, which is lower than expected (likely 12V or 24V).
3. Load Test with a 12V Car Bulb:
   • A 12V car bulb was connected between +VM and GND to add a load to the PSU.
   • The bulb lit up, but the output voltage remained at 7.4V and did not increase to the expected level (e.g., 12V or 24V).
   • This suggests the PSU is partially working but cannot fully activate or stabilize the correct voltage under load.
4. Tested PS_ON Signal:
   • Measured the voltage between PS_ON and GND to check for proper activation.
   • The voltage was -0.0015V, indicating no signal or a very low signal. This suggests that either the mainboard is not sending a proper PS_ON signal or the PSU is not responding to it.
5. Checked PSU Components:
   • Visual inspection of capacitors revealed no visible damage (e.g., no bulging, leaking, or physical signs of failure).
   • Tested the PSU for faulty capacitors, voltage regulators, and optocouplers:
     • Capacitors: No obvious damage, but deeper testing for internal faults may be needed.
     • Voltage Regulator: Output voltage was incorrect (too high in standby, too low for +VM).
     • Optocoupler: Not yet confirmed faulty, but could be part of the feedback circuit causing regulation issues.

Pictures:

• The PSU is delivering voltages but at incorrect levels. The standby voltage is too high (7.4V instead of 3.3V–5V), and the main output (+VM) is too low (8.43V instead of 12V or 24V).
• Forcing the PSU to start via PS_ON does not result in any changes, indicating an issue with the PSU's internal regulation or activation circuits.
• While the mainboard might not be sending a proper PS_ON signal, the PSU itself should still respond correctly when forced manually, but it does not.

What should I do next to fix the issue, or at least know exactly what the problems could be? I don't want to buy a new main board and find it unnecessary.


Update 28/11/24: @jayeff

Yellow: 3.34v ; White: 3,37v ; Brown: 3,37v.

Red: 0,80 ; Green: 0,80 ; Blue: 0,80 ; Purple: 0,80 ; Black: 0,80