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FLYBACK TRANSFORMER TESTING

flyback tester

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 transformer problems.
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 ground.
    e) Internal arcing between windings.
    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 load).
    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 winding.
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 voltage).
   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+ FET IRF630.
   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 transformer?
 

Capacitor shorted

Capacitor open

a.
No display (No high voltage). a. High voltage shut down.
b.
B+ voltage drop. b. Monitor will have ‘tic - tic’ sound. Sometimes the capacitor may measure O.K but break down when under full operating voltage.
c.
Secondary diode (UF5404) will burned or shorted. c. Horizontal output transistor will blow in a few hours or days after you have replaced it.
d.
Horizontal output transistor will get shorted. d. Sometimes it will cause intermittent "no display".
e.
Power blink. e. Distorted display ie, the display will go in and out.
f. Sometimes power section will blow, for example: Raffles 15” monitor. f. It will cause horizontal output transistor to become shorted and blow the power section.
g. Power section shut down for example: Compaq V55, Samtron 4bi monitor.    
h. Sometimes the automatic brightness limiter (ABL) circuitry components will get burned. This circuit is usually located beside the flyback transfomer. For example: LG520si    
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 to use.
   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 switch 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.*
   1) First set your multimeter to X10K range.
   2) Place your probe to point (D) and (E) refer to diagram.
   3) Point (D) is the anode red cap connected to the CRT. You must remove it in order to get a precise reading.
   4) Point (E) is any grounding of the monitor.
   5) If the needle of the multimeter shows a low ohms reading, this mean the internal capacitor is shorted.
   6) If the needle does not move at all, this doesn’t mean that the capacitor is O.K.
   7) You have to confirm this by using a digital capacitance meter which you can easily get one from local 
       distributor.
   8) If the reading from the digital capacitance meter shows 2.7nf, this mean the capacitor is within range (O.K).
   9) And if the reading showed 0.3nf, this mean the capacitor is open.
 10) You have three options if the capacitor is open or shorted.
   - Install a new flyback transformer or
   - Send the flyback transformer for refurbishing or 
   - Send the monitor back to customers after spending many hours and much effort on it.
* However certain monitors may have the value of 4.5nf, 6nf and 7.2nf.
Note: Sometimes the internal capacitor pin (F) is connected to circuit (feedback) instead of ground.

 

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