How To Speed Up Of Testing Electronic
Components-Part II
This is the second part on how to speed
up checking electronic components. Flyback transformer-well I guess
most of you all that deals with either TV or Monitor repair has
came across flyback transformer in the circuit. Whenever a flyback
transformer have problems it would cause power to cycle, high
voltage shut down, no power, low power, arcing, blur, too bright
and etc.
Now if you want to
check if the flyback transformer is okay or not your first step is
to check the internal capacitor with a digital capacitance meter.
It should have reading about 1.5 – 3 nano farad measuring from the
anode to the internal capacitor pin beneath the Monitor flyback.
Besides using digital capacitance meter to measure the internal
capacitor, you should also must use an analog meter set to X10 Kohm
range to test it.
There would
be no reading either way and if you got any readings then this
proof that the internal capacitor had developed a short circuit. If
the reading is okay then you can proceed to check the primary
winding of the flyback. The primary winding pins are the
HOT collector pulse and the B+ voltage in. You should check it on
board with a Dick smith flyback tester or with any flyback tester
that you have. If you are using the dick smith flyback tester, it
should show at least 4 or 5 bars and above. If the tester only
shows 1, 2 or zero bars then suspect something has gone wrong with
the circuit.
Remember, a shorted diode in the flyback
secondary side like the G1 or any other supply lines could pulled
down the reading in the dick smith flyback tester. For your
information, please don’t check the primary winding with an ohm
meter (whether it is an analog or digital meter) because normal
meters just can’t detect shorted winding in the flyback. Even if
there is only one shorted winding, by using a flyback tester, you
can easily find out the faults. A shorted horizontal output
transistor (HOT), horizontal yoke coil, B+ circuit components,
damper diode, safety capacitor may also caused the flyback tester
reading to drop. Just practice more on this circuit with the
flyback tester on different type of monitor so that it would be
easy for you to solve problems that are related to flyback
transformer.
Next is the fuse, you can easily check
it on board with your multimeter. Just set your meter either to
ohms or continuity. A good fuse should have reading (ohms value)
and beep sound if you select the continuity test. If no reading or
sound, 100 % the fuse is open and need replacement. Replace only
with the same ampere and voltage rating of fuse.
All Monitors and TV have a posistor used
to degauss (demagnetize) the picture tube. Normally, the whole
degauss circuit consists only the degauss coil, posistor and a
relay (for auto degauss). The posistor may have 2 or even 3 leads.
You can’t check the value of the posistor with multimeter. You have
to direct replace it if you suspect it to blow the fuse every time
when the equipment is turn “On” and the bridge rectifier is tested
okay. Sometimes you can remove the posistor and “shake” it to check
if you could hear any sound in it. If yes, then most probably
something has loosened inside and need to be replaced.
Monitors horizontal yoke coil can be
easily check with flyback tester too. You can even check it on
board and if the flyback tester shows 1, 2 or zero bars suspect a
defective yoke coil. In order to confirm it, you have to lift up
the yoke coils connector and directly measure it. If it still shows
the same result, then most probably the horizontal yoke coil had
developed a short circuit between the internal windings. Please do
not check with an ohmmeter or even with an inductance meter as both
don’t give accurate result when checking horizontal yoke
coil.
I
personally owns an inductance meter and when I compared a known
good yoke coil with a bad one, the result was still the same (good
inductance value) but when I compared and checked it with dick
smith meter, it clearly distinguish between the good and the bad
yoke coil. Horizontal yoke coils can breakdown when under full load
just like the flyback transformer, so be alert and if you can’t
solve any weird problems monitors especially power intermittent
cycling, horizontal width intermittently big and small with
pincushion out, HOT turned very hot in a short time then you have
to direct replace the CRT and retest again.
Vertical yoke coil can’t be test with
flyback tester and the good news is that the winding rarely give
problem. You should check it with an ohm meter to determine the
ohms value. If you have the expensive Sencore tester, you can
always check the vertical yoke coil for any short circuit between
the vertical windings.
In order to accurately check diodes, you
need to desolder one lead and test it with an analog meter set to X
10k ohms range. A good diode should have only one reading while the
bad one will have two readings. Be careful if you want to test a
schottky diodes as schottky diodes will have two readings but not
shorted readings. If you get two similar readings then the schottky
diodes is considered bad. You need semiconductor data book to help
you to determine if the diode belongs to which family (general
purpose, ultra fast recovery, damper, schottky diodes or etc).
However, if you set your meter to X 1 ohm and test a diode on board
and if you get two similar readings then chances are high the diode
have shorted. In order to confirm it you still need to remove one
of the lead from circuit. Assuming when an equipment came in with a
blown fuse (fuse became dark), this sign shows that the equipment
might have a major short circuit somewhere in the circuit (mainly
power supply area). Using your analog meter set to X 1 ohms to
check on the bridge rectifier on board you can easily tell if the
any of the bridge diodes have shorted. Compare reading with a known
good equipment and I’m sure you will understand about checking
diodes on board.
Checking zener diodes, you have to
remove one lead from the board. Before you check on any zener
diodes, you first need to identify what is the voltage of the zener
diodes. Refer to semiconductor data book for any codes printed on
the body of zener diodes. Once you know the zener diode voltage, by
using again analog meter set to X 10 K ohm range, you will quickly
determine if the zener diode is faulty or not. Any zener diodes
from 2.4 volt to 12 volt should have two readings but not shorted
readings and any zener diodes that have 13 volt and above should
have one reading. You can check also zener diode on board if only
the zener diode developed a direct short circuit which is easily
measured with an analog meter set to X 1 ohm range. Remember to
replace zener diode only with the same voltage and for the wattage,
it can be the same or a little bit higher.
There are two different ways to test
capacitors. One for the electrolytic capacitor and the other one
for the non-polar or the ceramic type capacitor that do not have
polarity. I will start explaining the electrolytic capacitor first.
I believe many of you already own the ESR meter for testing
electrolytic capacitor on board. There are many types of ESR meters
in the market nowadays. Brand name such as the famous Dick Smith
ESR meter, EDS Capanalyzer 88a, Tenma, B& K Precision, Cap
Wizard, Peak Electronics and etc. No matter what ESR meter you use,
the result you get will be the same which is checking the ESR Ohm
of the electrolytic capacitor while it still on board. We all knew
that it is quite accurate to measure e-caps while it still in
circuit but do you know that ESR meter can’t test e-caps on all
type of circuit? I’m not frightening you or make you to lost
confidence in using ESR meter. I myself also use ESR meter to check
for bad e-caps everyday. I just can’t part it away with this ESR
meter. Without one I will have a hard way to find the defective
E-caps.
What I mean ESR meter can’t test
accurately on board in all circuit was that it depends on what type
of circuit you are checking! If you check on the Monitor heater
circuit, it would not give you an accurate reading because the
heater line is eventually go to cold ground through the filament
inside the CRT tube. In other words you are actually measuring the
low resistance winding of the filament. The same case also happen
if you try to check any E-caps that have a low ohm resistor
parallel with the e-caps that you want to check. Another good
example would be the secondary output lines. Have you ever come
across secondary output lines that have few electrolytic capacitors
along the same line? Yes, that’s mean if one of the e-caps turned
bad the ESR meter would test the E-caps as good because the same
line have another good e-caps there. Don’t be discouraged by the
examples that I’ve explained above. In fact those are not just
examples; it was the real life experienced that I had encountered
as electronic repairer.
Do not worry about the above
explanations as there are solutions for it. First, before using ESR
meter on any e-caps, please make sure to ask yourself “what kind of
circuit that I’m checking now?” If it is a heater circuit or
secondary output lines that have few e-caps that connected in
parallel, you have to desolder one lead of the e-caps and test it
with your ESR meter. Otherwise you would not get an accurate result
from your ESR meter. After reading the above example I’m sure you
would be careful next time when you want to check for bad e-caps on
board. One more advice, never check the e-caps with a digital
capacitance meter as a bad e-cap the meter will tell you it is good
and you will be wasting of your precious time trying to find out
the real fault in the equipment.
Next is the non polarity capacitor, you
have to desolder on lead in order to test the capacitance. You
can’t measure the non polarity capacitor on board as the digital
capacitor meter doesn’t have the capability to check on board not
like the ESR meter. After you have confirmed that the capacitance
is good you need to perform another test which is using analog
meter set to X 10 k ohm to check for any short circuit between the
internal plates. If the capacitor that you want to check rated
several hundreds volts then I guess you have to use an insulation
tester to check it. In other words, your analog meter does not have
the feature that can pump in hundreds of volt to a non-polarity
capacitor. Just let the insulation tester do the job.
The last component that I want to share
in this article is the bipolar transistor. You can actually check
transistor on board without removing it to speed up your repair
work. First you must know as which types of the transistor that you
want to measure belong to. It can be either NPN or the PNP.
Assuming you have checked that the transistor is NPN type, then
desolder the base and the collector pin. Do not desolder the
emitter pin. Place your analog meter black probe to base (meter set
to X 1 ohm) and the red probe to collector and then to the emitter
pin. It should give two similar reading but not shorted readings!
Now set your meter to X 10 K ohms and place your meter probes to
the collector and the emitter pins (either way). Some good
transistors can show no reading on both ways while some will show
only one reading but not shorted reading. If you get two readings
then the transistor is considered bad and need
replacement.
Conclusion- I really hope that you can
start practicing the methods that I’ve covered in the part one and
part two of this articles. Hands on practice only make us perfect
and the result would be you can check any electronic components in
the shortest time and accurate too. However, you have to remember
that electronic components can test good but breakdown when under
full load. Your
experience will tell you if the components need a direct
replacement. That’s all for today and see you again on next
weekend.God Bless!
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