Price Troubleshooting And Repair Power Supply The Easy Way Apollo The Great - Apollo 21 Tube. Duration : 2.68 Mins.
Music video by Apollo The Great performing 21. From the album "Apollo 21 (Deluxe Edition)" available on iTunes: itunes.apple.com
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Troubleshooting linear power supply was quite easy as compare to switch mode power supplies (SMPS). AC voltage enters to the primary side of linear transformer and then converted the AC into a lower or higher AC voltage depending on the secondary winding. The output AC voltage is then rectified and filtered by a diode and capacitors to produce a clean DC voltage. If there is a problem in the linear transformer circuit, I can say that it is very easy to locate the fault. This is somehow different in the case of a switch mode power supply. The designs were complicated and some technicians found it quite hard to fully understand how the switch mode power supplies work.
The working principle of switch mode power supply is different from the linear type. First the AC voltage willflow to a full wave rectifier (bridge rectifier) which produces an uneven DC output and then filtered by a large capacitor (usually 220 micro farad and up to 450 volts). The clean DC voltage will then flows to start up resistors and the input of switch mode power transformer. Once the voltage passed through the high ohms resistor (start up resistors) the voltage would drop to a value where it then flows to the VCC supply pin of Pulse width modulation IC.
Once the PWM IC received the voltage it will output a signal to drive the transistor (or FET) and produces a magnetic field changing in the transformer primary winding. The changing magnetic field induces voltage in the secondary windings. Each of these AC voltage produced by the secondary windings is then rectified, filtered,and regulated to produce a clean DC voltage. One of the main DC output voltage is the B + supply to flyback transformer that (for TV and Monitor Circuit)
The output from the B + voltage supply is then connected, through a "feedback" loop (which consist of optoisolator ic and an error amplifier IC TL431), back to the PWM IC. When the voltage from the B + supply rises or drop a bit, the PWM IC will act to correct the output.
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If you still do not understand the above explanation, please do not be discourage because you can always buy technical books and schematic diagrams and read it till you get the whole idea of how a SMPS work. You can ask a repair friend or even surf the internet for a better and easy explanation.
Here I would like you to download a freeSMPS article by Sencore and I found it to be a great help for you who are still struggle on how SMPS work and how to troubleshoot when it fails. You must ask your self what is the purpose and its function of the components in the SMPS circuit and how to check them if they fail. Find out on your own the function of these components in SMPS circuit:
Bridge rectifier,
Filter capacitor,
Start-up resistors
Chopper/Power FET
Pulse Width Modulation (PWM IC)
Current sense resistor
Switch mode power transformer
Optoisolator/optocoupler
Error Amplifier IC (TL431)
Secondary diodes
Secondary filter capacitors
Push yourself further by searching the internet for the datasheet of a PWM IC part number. For example, UC3842 PWM IC ismostly used in SMPS. Do you know what the function of pin 5 of this IC is? Do you know which pin to the VCC supply enters? Do you know what the actual voltage that flow to the IC is? Do you know which pin that drives the power FET? Can I get a replacement for this IC? And so on … … …
Let's take a soldier as an example. Soldiers not only good in handling rifle but also knows all the details about it. They know how to dismantle and assemble back their rifle fast (the picture in the middle of war the rifle jammed-they can repair it fast). They know how much each bullet cost, how far the shooting distance, how big is the diameter of the bullet, how many inches the length of the bullet and so on. Hope you don't get bored with the soldier's story, did you get theideas?
Any SMPS that comes across my repair bench, I would not immediately repair it, in fact I will take couples of minutes to analyze the circuit design and see it from all angles before I begin to repair. Troubleshooting SMPS is not limited to only one procedure in fact many electronic repairers have their own unique ways and methods to solve SMPS problems. Some prefer to use light bulb to isolated SMPS faults while others like to use resistors. Troubleshooting SMPS is fun and flexible but in some cases could make you get very frustrated too.
