Power LED Does Not Light Up
When you see an equipment where the power LED does not light up don't quickly decide that it was the power section problem. You have to know that nowadays the consumer electronics equipment power LED signal is coming from the mainboard MCU. This mean if the mainboard MCU have problem or no supply voltage to the MCU then there will be no signal going to the power LED and this will cause the LED would not light up.
If this case happen and if you put your concentration on the power section you will be wasting your time. You must first determine that there are output voltages from the power supply before checking on the mainboard. If there is no or low power output from the power supply then you can troubleshoot the power supply ection.
I brought up this subject is because I do get many emails about beginners wrongly diagnosed the problem and ended up could not repair the fault. The reason was because the fault lies in the mainboard and not in the power supply section. You have to take note that whatever complaint or any funny/weird symptoms, always make sure the switch mode power supply have constant and stable output voltages. This is the first section that you need to check before moving to other circuits.
If there are good output voltages then you can move on to other circuits to start using voltage or even scope to pin point any unstable or abnormal waveform. In electronics troubleshooting please do not make things complicated because this will drag you more time and it could end up you could not repair the equipment.
In order to make the repair work simple always study the schematic diagram of that equipment and draw your own block diagram for your own easy reference. Once you have your own block diagram you can repair model of that type of equipment without having to always refer back to each model schemactic diagram. Unless if there are components burnt or missing then you really need to look for the schematic.
As mentioned earlier that nowadays many equipment are using MCU in the mainboard and this MCU could post many funny problems. If you have checked that the corresponding or surrounding components are good which includes the supply voltages then suspect either the MCU, EEPROM (of even flash rom if there is one) data have corrupted.
I have came across lots of mainboards, if the SMD voltage regulator ICs are good then very high chances those memory ICs have problem. It is tough to locate the exact part with orginal data inside the MCU unless you have earlier retrieved a good working programs. Nowadays manufacturers have made it tougher for us as a repairer because they have made MCU where you can pump in good data but would not be able to retrieve/save the data from the MCU. The only way to solve the problem is to replace with a new board or you can try to buy a used board from Ebay.
Hope this post could be a help to you. If you would like to share about your repair experiences please do leave a comment below-thanks.