TV does not turn on: no standby light, step-by-step checks
The TV is plugged in, the standby LED is dark, and the remote does nothing. This is one of the most common complaints, and it is nearly always a power supply problem, so the right approach is to follow the power from the mains inward and stop at the first thing that is wrong.
Part of the Boards and faults guide.
Safety. The power supply carries mains voltage and the primary side can be live even when the set looks off. Use an isolating transformer, unplug the set before touching anything, and discharge the high-voltage capacitors before you put your hands on the board. Never touch the primary side while the set is powered. Backlight circuits can also carry high voltage. If you are not trained for this work, do not open the set.
Symptoms
- No LED, no click, no sound, no picture.
- Sometimes a faint tick or a short flash of the LED followed by silence. That points to protection, which is a different checklist.
Step-by-step checks
This sequence follows the “Dead: no LED, no reaction” checklist from the FW Tool diagnostics reference, which is general repair practice and not taken from a manufacturer’s documentation.
- Mains cord and outlet. Try another cord and another socket. Look at the power connector for burn marks.
- Fuse on the power supply. A blown fuse often means a short on the primary side. Do not just fit a new one and switch on; find out why it blew first.
- Line filter, NTC and bridge rectifier. A shorted bridge or a shorted switching transistor is a typical cause of a blown fuse. Test the parts with the set unplugged and the capacitors discharged.
- Bulk capacitor voltage. With the board powered, and only if you can do it safely with proper isolation, the main bulk capacitor should show roughly 300 V on a 230 V mains. If this voltage is present but there is no standby voltage, suspect the standby PWM IC, its start-up resistor, or the switch.
- Standby rail. Check the 5 V or 3.3 V standby rail at the connector to the mainboard. If it sags, disconnect the loads one by one to see which one pulls it down.
- Secondary electrolytic capacitors. Look for bulging, then measure ESR, especially around the PWM feedback loop. See checking electrolytic capacitors by ESR.
- Optocoupler and TL431. These form the feedback loop. If they fail, the standby voltage can run too high or too low.
Exact rail voltages, pin numbers and part values differ by model. UNVERIFIED Check them against the service manual or schematic of your chassis before drawing conclusions.
Typical mistakes
- Replacing the fuse without finding the short, which destroys the new fuse and sometimes more.
- Measuring on the primary side with a grounded oscilloscope or meter and no isolation.
- Blaming the mainboard first. If the standby rail is missing, the mainboard is rarely the cause.
- Replacing only the one capacitor that looks bad. Others from the same batch are often close behind.
- Skipping the discharge step because the set has been unplugged for a while.
- Not writing down what was found. The same chassis comes back, and notes save time.
How this is done in FW Tool
- The “TV diagnostics” tab in the reference holds the checklists, including this one, together with a safety reminder about the mains and backlight voltages. The tab is marked as general practice, not manufacturer documentation.
- The ESR table and calculator in the reference let you compare a measured value with typical values by capacitance and voltage.
- Once the cause is found, the repair log keeps the fault, the work and the parts in one card, and tells you when you have already repaired the same model. See the repair log and customer documents.
- If the set lights up later but misbehaves, the faults database for mainboards may already describe it: typical faults by mainboard family.
The full list of tabs is on the features page.
FAQ
The standby rail is correct but the TV still does nothing. What next?
Then the power supply may be fine and the problem is further on: the power-on command from the mainboard, the mainboard itself, or a protection circuit. The other checklists in the diagnostics reference (LED on but black screen, turns on and off, boot loop) take over from here.
Can I test the set by briefly powering it with the backlight unplugged?
This is a common diagnostic step for sets that switch off immediately, and the reference checklist includes it. It is not a substitute for the safety rules above.
Is a blown fuse always a power supply fault?
It is usually a primary-side fault. In rare cases something downstream loads the supply heavily, which is why you check the rails before declaring the job done.