LOPT - FLY-BACK EQUIVALENCE EHT TRANSFORMER COMPARATION TABLE ORIGINAL ---> HR DIEMEN SPARE PART LIST 25
Here below a list of the original Flybacks LOPTS of many CRT TVs.
These DC flybacks are found in every CRT computer monitor and are called
the DST flybacks (diode-split transformers) because of the several high
voltage diodes and secondaries inside. In addition to the high
resistance resistor cascade (Bleeder) and focus/screen tuning
potentiometers described above, these kinds may have an integrated high
voltage filtering capacitor (few nanofarads at >=30 kV), or –
optionally – a HV capacitor for dynamic focus.
The TV DC flybacks are
also diode-split (DST), however these are found in every modern CRT
TV-set from mid-end 80s and onwards. These have just two screen-tuning
potentiometers and no internal capacitors whatsoever !
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Comparison list is organized with original code to the HR DIEMEN corresponding Replacement part.
FLY-BACK EQUIVALENCE
Line
Output Transformers (LOT, LOPT, LOPTx)
Fly-back Transformers (FBT)
Integrated
High Voltage Transformer (IHVT)
Nowadays, more and more monitor comes in with flyback transformers problems.
Testing flyback transformer are not difficult if you carefully follow the
instruction. In many cases, the flyback transformer can become short
circuit after using not more than 2 years. This is partly due to bad design
and low quality materials used during manufactures flyback transformer.
The question is what kind of problems can be found in a flyback transformer
and how to test and when to replace it. Here is an explanation that will help
you to identify many flyback transformer problems.
There are nine common problems can be found in a
flyback transformer.
a) A shorted turned in the primary winding.
b) An open or shorted internal capacitor in secondary section.
c)
Flyback Transformer becomes bulged or cracked.
d)
External arcing to ground.
e)
Internal arcing between windings.
f) S
horted internal high voltage diode 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.
Testing flyback transformer will be base on (a) and (b) since problem
(c) is visible 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. Different monitor have
different type of flyback transformer design. Problem (i) can be checked using an
ohm meter measuring between primary and secondary winding. A shorted turned or open
in secondary winding is very uncommon.
What type of symptoms 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.
What type of symptoms will appear if a capacitor is open or shorted in a flyback transformer?
Capacitor shorted
a. No display (No high voltage).
b. B+ voltage drop.
c. Secondary diode (UF5404) will burned or shorted.
d. Horizontal output transistor will get shorted.
e. Power blink.
f. Sometimes power section will blow, for example: Raffles 15 inch monitor.
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 transformer. For example: LG520si
Capacitor open
a.
High voltage shut down.
b. Monitor will have ‘tic - tic’ sound. Sometimes the capacitor may measure O.K. but
break down when under full operating voltage.
c. Horizontal output transistor will blow in a few hours or days after you have replaced it.
d. Sometimes it will cause intermittent "no display".
e. Distorted display i.e., the display will go in and out.
f. It will cause horizontal output transistor to become shorted and blow the power section.
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) This meter is handy and easy to use.
d) Just simply connect the probe to primary winding.
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.
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 anode and cold ground.
3) You must remove the anode cap in order to get a precise reading.
4) Cold ground means the monitor chassis ground.
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 is connected to circuits (feedback) instead of ground.
Tv rca flyback transformer circuits usually do not have a internal capacitor in it.
If you have a flyback diagram and circuits which you can get it from the
net, that would be an advantage to easily understand how to check them.
Line transformers generate the necessary deflection pulse and other many key voltages and the high voltage for anode of the picture tube in tube televisions and computer monitors. Usually this is around 30 kV for a color device, but the current is with approx. 0.5 to 4 mA.
The line transformer or horizontal output transformer (English: flyback transformer or line output transformer) is part of a television / monitor with picture tube. It is used to supply the line deflection coil of the deflection system and at the same time usually also to generate the high voltage of 20 to 30 kV required for the operation of the picture tube and other voltages necessary for the operation of the device.
Line transformers work with the line frequency, with European TV sets with 15.625 kHz. Line transformers of 100 Hz televisions work at twice the frequency, i.e. at 31.25 kHz. In monitors, the line transformer is operated at different frequencies, which depend on the resolution of the image sent by the computer. For example, the line frequency of a monitor with a resolution of 1024 × 768 pixels and 85 Hz vertical frequency is approximately 68.7 kHz. With these frequencies, the line output stage switches a switching tube or today a switching transistor, which are used to control the line transformer.
The whistling noise of some older monitors and most older, conventional TV sets arises from the fact that mainly the line transformer, but also other components such as coils and capacitors, are mechanically excited to vibrate by the occurring magnetic and electrostatic forces. Whistling has a frequency of 15.625 kHz due to the European television standard. TVs with 100 Hz technology and most high-resolution computer monitors whistle outside the listening area........
Line transformers are potted with resin and have a ferrite core and are therefore of course only suitable for high frequencies in the kHz range. Newer types, so-called diode split transformers, contain many individual diodes between the windings and thus supply a rectified high voltage (pulsating DC voltage). Older models made of black and white devices have an external cascade, the direct (high-frequency) output voltage is then only about 8 kV, but a little more current is available with such AC line transformers. Line transformers require an electronic control circuit which provides a square wave signal in the range of approx. 15 kHz.
Diode split transformer with permanently cast diodes and DC output The advantage of line transformers: They are easy and inexpensive (or free) and can be obtained in large numbers at radio / TV shops and in computer shops where devices are disposed of. Especially nowadays, in which tube monitors have to make room for flat screens, many old monitors and TVs are disposed of.
Removal and wiring of a line transformer:
Important when removing the line transformer from the TV or monitor: First discharge the picture tube, then remove the high-voltage connection, and draw out the pin assignment of the line transformer before unsoldering. Two connections are particularly important: supply supply (approx. 150V from the power supply unit) and connection that goes to the collector of the horizontal output transistor or on very older types to a tube or thyristor final stage.
The thick, well-insulated, red cable is the high-voltage output (approx. 30kV), while the somewhat thinner, black cable carries the focus voltage, which is only around 6kV. Finally, the orange cable brings the grid 2 voltage, which is only a few hundred volts. Television and monitor flyback transformer pinout have some common designed except that the monitor flyback have a internal capacitor built in. The internal capacitor value have around 2.7 nanofarad to 4.5 nanofarad to improve the picture quality especially when the monitor which can go for a higher resolution compare to Tv. If without the internal capacitor in the monitor flyback the display will curve or slightly out of shape especially at both the right and left hand side of the picture and may present other imperfections not admitted for monitors. It acts as a filter. Internally they may have a high vealue resitor (600 to 900 mega ohm) in parallel to HV output. This to adapt the ouput impedance of the LOPT to the CRT Anode.
Mostly tv and monitor flyback transformers have about ten pins at the bottom of the flyback. Each of the pin have a purpose or function as part of a complete circuit. The common pins that you can find in monitor flyback are: B+ pin, Horizontal collector pulse, ABL (automatic blanking limiter), GROUND, G1, AFC (automatic frequency control), VCC, HEATER (to filament) and X-RAY protection.
The B+ and horizontal collector pulse pin forms one winding which we call it as flyback primary winding. It can only can be test by using a flyback meter such as the Lopt tester flyback transformer pinoutor sencore LC102 and LC103C.
Note that some monitors and TV design may have a separate HV and deflections circuits
.
Normal meters can't check this kind of fault. This is the most important winding compares to others and it can easily developed a short circuit when B+ voltage line or Horizontal output transistor (HOT) shorted. Sometimes a shorted internal capacitor in the flyback transformer may cause the primary winding to burn internally and the flyback became bulge and poured out the epoxy.
Other pins are the ground, G1, and AFC winding. AFC stand for automatic frequency control and it send signal (pulse) from the flyback transformer to the horizontal oscillator ic to lock or synchronize the frequency of the monitor. If this AFC line fails the picture will shift either to the far left or far right. There is no way that you can adjust the picture to the center even with the internal adjustment in the mainboard. The purpose of G1 voltage is to pull the electron generated from the cathode (after the heater or filament heat up) and passed it to G2 which is the screen voltage.
G1 normally is a negative voltage or positive from few volts to 32 volts in some most ancient designs . Most tv picture tube do not use G1 voltage. If the G1 voltage is missing or zero voltage to the picture tube the monitor display will becomes very bright with retrace lines (diagonal lines or flyback lines) across the screen and sometimes the monitor will goes into shutdown mode.
ABL stand for automatic beam limiter- I refer it as a limiter further circuit. Why? because whenever there is a contrast or bright problem i will search for this pin and begin to trace from there. Normally a resistor increased in resistance and a shorted ceramic capacitor caused the display to become dim and you may think it might be the fault of a bad CRT.
Heater or filament pin nowadays hardly found in monitor flyback because the crt heater voltage now is derived directly from the switch mode power supply. However heater pin is still can be found in television flyback transformer. If the anode voltage is too high (more than 30 kilovolt), the x-ray protect pin will send a signal to horizontal oscillator ic in order to disable the horizontal drive waveform THIS FOR SAFETY REASONS.
Without the horizontal drive pulse the high voltage generated by the flyback will collapsed and protect the user from excessive x-ray.
The flyback transformer pinout will also generate high pulse ac which later convert to dc through an ultra fast recovery diode. For your information, the ac pulse generated by the flyback transformer cannot be check with our normal analog or digital meter. the frequency is so high and you need a special meter to do the job. The dc voltages are then supply to various circuit such as the vertical output circuit. If you understand all the functions of each flyback transformer pinout, repairing monitor or tv will be much easier and save your precious time.
The variety of transistors and diodes in TV sets has increased a lot today, greatly decreasing their availability in electronics stores. Although it may seem simple, often finding a replacement transistor or diode can be a chore. The fact is that it is not so simple, it is not just to check the main characteristics (Voltage, Current and Power) and if it is NPN or PNP, or if it is a zener or common diode. In addition, knowing the meaning of the encodings used in the nomenclatures of these components also helps a lot and greatly simplifies the work.
