I received this email a few days ago from Mr. matt stolte from Massillon -United States of America.
Sir I have read your basic electronics book course and loved it. I have been doing flat screen TV repair for about 2 years and now have my own business doing it.
I knew nothing about electronic before I started. And can easily diagnose and troubleshoot a TV and get if fixed. Normally I just swap boards unless I see some blown caps.
However I am trying to get down to component level, there is 3 things I'm trying to learn.
1 how to trace circuits to see what component controls what
2 how to locate a short where it is on PSU or main
3 if power supply doesn't have the 5v standby how I can find the bad component what components are in charge of the standby voltage
Now I'm dealing with LCD, led, plasma only
Thanks in advance
From the email Matt has raised very important questions on troubleshooting and repair at the component level and for that reason I wish to shed some light on the same.
1. How to trace circuits to see what component controls what
Modern electronics equipment contains hundreds or even thousands of components, if it’s your first time to open an electronics device like Television or computer monitor, one is usually intimated by the many components in there which look more of less like a big city connected with roads.
But if you have a good understanding on basic electronics you will notice that these are usually common components and therefore no need to panic.
This is because electronics equipment is a product of many different components (both passive and active) which work together to build a Television, DVDs, Radios or whichever other electronics equipment you see in the market.
Just like we have maps to navigate a city, we also need electronics maps to navigate electronics gadget and here I am going to explain 3 road-maps.
The block diagram helps you understand the signal flow and connections between circuit sections so you can see how they are supposed to work with each other.
The schematic diagram shows you individual components and stages so you can zero in on specific components you may want to scope or pull for testing
As the name implies this include drawings of the actual parts and shows their interconnections detailing the placement of components as they exist on circuit boards.
The best source to get these is the internet, you can easily search and get hold of them seamlessly.
2. How to locate a short where it is on PSU or main.
A Shorted component in the supply or any part of the circuit can be a source of stress to any technician.
Shorted components on the primary supply usually cause instant blowing of the safety components like the fuse or surge limiter, so next time you find any of this component open don’t just replace them and apply power because chances are high they are going to blow again unless you want to keep the manufacturer of those components in business.
The most suspect components which fail by shorting includes, transistors, diodes, ics, capacitors…
Most of them fail catastrophically and therefore you will not need any meter to confirm besides your set of eyes.
Sometimes components also short without any visual signs and this is where meter comes in handy.
Component which short usually have one leg on the live line and other leg on the ground, so after the component short it actually join the live and the ground together.
Usually electrolytic capacitors are used to filter line voltages and therefore have one leg on the live and the other on the ground.
So the best place to start troubleshooting a short line is testing between the positive (+) and negative (-) pins of electrolytic capacitors.
For example testing across the main capacitor with your meter set to low ohm should tell you if the line is shorted or not.
Please note that getting low ohm reading across the capacitor is not an indication that the actual capacitor is shorted but indicate a shorted component on that line which the capacitor is filtering.
You may decide to lift one leg of the component on that line one by one till you stop getting the beep, the last component to isolate and the beep disappear is the actual culprit.
If you suspect an ic is shorted just solder out the main supply pin of this ic and test again and if the beep is gone then the ic is the culprit.
Transistors usually short C-E junction and therefore whenever you test these two legs with a meter and find same reading either way of the meter means it is shorted.
3. If power supply doesn't have the 5v standby how I can find the bad component what components are in charge of the standby voltage.
Standby power is electrical power used by appliances or equipment when not performing their primary functions, often waiting to be activated by remote control or power on button.
A good example is the computer ATX power supply, if you get a new ATX power supply and check its output voltages, you will not get any voltage except on the violet line.
This is called standby voltage and always have +5 volts. To activate other voltages then you will have to press the power on button on your computer or if the supply is not connected to the computer then just hook the green pin (PS-ON) to the ground and other voltages will show up...
If you find the standby voltage is not present don’t continue troubleshooting until you get what is blocking this voltage, trace backward to locate what is blocking it.
All the best guys