Secrets On Power Supply
Repair and Troubleshooting-Solving Problems And Failure in Switch
Mode Power Supplies
A Switch Mode Power Supply
power supply repair is one of the most challenging tasks for an
electronic repairer and once you have mastered the circuit and
repair technique, to troubleshoot other types of circuit such as
the color, vertical, audio, high voltage and so forth will be
faster. If you are well known of how power supply or switch mode
power supplies work, you are ready to repair any kind of power
supply problems in any types of equipment. Basically, all of the power
supply functions are almost the same which is to produce output
voltages for various secondary circuits. Once you know how a power
supply work you will know the rest of it.
problems can happen in the primary or secondary section.
Even if there are some problems in the furthest part of any
equipment circuit such as a shorted ic or transistor in a Monitor
color circuit board, the power supply may not work or just blink.
There are many methods of troubleshooting a power supply; I will
explain one of my ways on how to repair it.
Whenever a power
supply sent for repair whether it is a Monitor switching power
supply or computer Atx power supply I will test the power supply
first before open up the casing. Power supply problems can be
categorize into no power, low output power, power supply cut-off
after sometimes or once switch on, power blink and higher output
problems are I will use a standard procedure method to test it.
-check the on/off switch, fuse and
discharge the large filter capacitor-if the fuse burnt into dark
color then expect heavy short circuit in the power supply section.
It could be a shorted bridge rectifier, a shorted power transistor or even a shorted power ic. Don’t
under estimate that a shorted primary winding in the switch mode
power transformer can occurred. If the fuse is just a slight torn,
may be the fuse spoilt by itself because fuse have lifespan too.
Most of the time, replacing only the fuse will solve the no power
-make sure all secondary diodes
are working. You can either remove one of the diodes lead to
accurately check it or you can use a flyback tester as describe in
-check horizontal output
transistor, b+ fet and flyback transformer if you repair a Monitor.
Anytime, if either one of these components have
failure, it will affect the power supply
functions. Testing fet
and flyback transformer can
be read by clicking on the blue link.
-Check all electrolytic capacitors
with esr tester in the primary and secondary section- if there are
some electrolytic capacitor failure in the power supply section
(either primary or secondary area) the power supply will blink,
produced low output power or totally no power at
-Test the primary winding of
switch mode power transformer with flyback tester. Check also the
flyback primary winding, b+ coil winding and horizontal yoke coil
if you repair monitor. One of these coils shorted can cause power
to shut down, blink, and no power.
If you have confirmed that the secondary
side of power supply components is working then what you need to do
is to desolder all the components in the primary side and test all
the components in it. This is where your real troubleshooting skill
is needed. Understanding and know how to test basic electronic
components is very important otherwise you will be facing
difficulty in finding the fault. If you are new in this electronic
repair line, I highly recommend that you check every single
component in the power supply circuit and once you got hold of it,
you can then locate fault by voltage testing or even identify fault
Read all my articles on how to
check basic electronic components. Primary side of power supply
normally has about less than 30 components and it will take you
less than 20 minutes to test all of them. Many times there are more
than one component found to be faulty and by replacing only that
particular component won’t solve the problem. Once you have
completed the entire components test and already replace the
necessary parts, you have to power up the power supply by using a
100 watt bulb connected across the fuse holder.
If the bulb lights very bright and
won’t go off even after couples of minutes then there are still
problems in the power supply. If the bulb goes dim or went off, you
know that the shorts had been taken care and you now can switch on
the power supply confidently and won’t blow the fuse
If you want to be an expert in
power supply repair, one have to practice, read and fully
understand how basic electronic components and power supply work.
With all these knowledge in your mind and hand, I believe there
will be no power supply problems that are too difficult for you to
repair. All the best to you.
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a Professsional in Switch Mode Power Supply