Monitor & TV
Repairer - The Secrets on How To Testing Flyback Transformer (FBT) or LOPT
1. Nowadays, more and more monitors comes in
with flyback transformer problems. In
many cases, the flyback
transformer can become short circuited within one and a
half years after being
serviced.The question is what kind of problems can be found
in a flyback transformer
and how to test it. Here is an explanation that will help you to
identify many flyback
2. There are
nine common problems to be found in a flyback transformer.
a) A shorted turned (C)
in the primary winding.
b) An open or shorted
capacitor (C1) in secondary section.
c) Flyback Transformer
becomes buldged or cracked.
d) External arcing to
e) Internal arcing
f) Shorted internal high
voltage diode (D1) in secondary winding.
g) Breakdown in focus /
screen voltage divider causing blur display.
h) Flyback Transformer
breakdown at full operating voltage (breakdown when under
i) Short circuit between
primary and secondary winding.
3. Explanation will be base on (a) and (b)
since problem (c) can be seen with the
naked eyes while problem
(d) and (e) can be detected by hearing the arcing sound
generated by the flyback
transformer. Problem (f) can be checked with multimeter
set to the highest range
measured from anode to ABL pin while (g) can be solved by
adding a new monitor blur
buster (For 14' & 15' monitor only.) Problem (h) can only
be tested by substituting
a known good similar Flyback Transformer. Problem (i) can
be checked using an ohm
meter measuring between primary and secondary
4. A shorted
turned or open in secondary winding is very uncommon.
5. What type
of symptom will appear if there is a shorted turned in primary winding?
a) No display (No high
b) Power blink.
c) B+ voltage drop.
d) Horizontal output transistor
will get very hot and later become shorted.
e) Along B+ line components
will spoilt. Example:- secondary diode UF5404 and B+
f) Sometimes it will cause the
power section to blow.
6. What type
of symptom will appear if a capacitor is open or shorted in a flyback
voltage shut down.
High voltage shut down.
b. Monitor will have "tic -
Sometimes the capacitor may
break down when under full operating
Secondary diode (UF5404) will burned
c. Horizontal output
transistor will blow in a
few hours or days after you have replaced
Horizontal output transistor will get shorted.
d. Sometimes it will cause
e. Distorted display ie, the
display will go in
Sometimes power section will blow, for
Raffles 15 inch monitor.
f. It will cause
horizontal output transistor to
become shorted and blow the power
Power section shut down for example:
Compaq V55, Samtron 4bi monitor.
Sometimes the automatic brightness
circuitry components will get
circuit is usually located beside
flyback transfomer. For example:
7. How to
check if a primary winding is good or bad in a Flyback Transformer?
a) By using a flyback/LOPT
tester, this instrument identifies faults in primary winding
by doing a ring test.
b) It can test the winding even
with only one shorted turned (C).
c) This meter is handy and easy
d) Just simply connect the
probe to point (A) and (B) refer to the diagram.
e) The readout is a clear bar
graph display which show you if the flyback
transformer primary winding is good or shorted.
f) The LOPT Tester also can be
used to check the CRT YOKE coil, B+ coil and
mode power transformer winding.
NOTE: Measuring the resistance winding of a
flyback transformer, yoke coil, B+ coil
and SMPS winding using a multimeter can MISLEAD a technician into
believing that a shorted winding is good. This can waste his precious
time and time is money.
8. How to
diagnose if the internal capacitor is open or shorted?
By using a normal analog
multimeter and a digital capacitance meter. A good
capacitor have the range
from 1.5 nanofarad to 3 nanofarad.*
a) First set your multimeter to
b) Place your probe to point
(D) and (E) refer to diagram.
c) Point (D) is the anode red
cap connected to the CRT. You must remove it in order
to get a precise reading.
d) Point (E) is any grounding
of the monitor.
e) If the needle of the
multimeter shows a low ohms reading, this mean the internal
capacitor is shorted.
f) If the needle does not
move at all, this doesnt mean that the capacitor is O.K.
g) You have to confirm this by
using a digital capacitance meter which you can easily
get one from local distributor.
h) If the reading from the
digital capacitance meter shows 2.7nf, this mean the
capacitor is within range (O.K).
i) And if the reading showed
0.3nf, this mean the capacitor is open.
j) You have three options if
the capacitor is open or shorted.
Install a new flyback transformer or
the flyback transformer for refurbishing or
the monitor back to customers after spending many hours and much effort
certain monitors may have the value of 4.5nf, 6nf and 7.2nf.
Author By : Jestine Yong