Secrets On Power Supply Repair and
Troubleshooting-Solving Problems And
Failure in Switch Mode Power Supplies
A Switch Mode Power Supply
The 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.
Power supply 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 voltage.
Whatever the 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 supply symptoms.
-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 this
article.
-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 sectionif 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 all!
-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 by section.
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 again.
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.