Most of the technicians certainly never experienced anything like this, where when he discovered the transistor HOT (horizontal output transistor) are damaged, and then replace them with new ones, but when trying to turn the transistor was a while back damaged.
Why does this happen?, Here are the things that cause instant damage suffered HOT transistor:
1. Resonant Capacitor
Resonant capacitor or the so-called safety capacitor / capacitors damper located at the collector transistor HOT shock mounted to reduce the voltage generated by the flyback transformer in a way to fill absorb these voltage capacitors, these capacitors typically have a working voltage of 1.6 kV, if capacitor damaged, short, capacitance decreased or solderanya loose, then there is nothing to absorb the shock voltage that causes the transistor HOT damaged instantly.
How could this happen?, Let's do the following experiment to obtain a clearer picture:
- Prepare a transformer power supply that is usually used for an amplifier or a radio / tape / DVD Compo is still good. If you can find imported brands transformer is not a local transformer
- Take the AVO-meter and set at X1 position
- Hold the red and black probe on the metal-contacts / tip of the plug (not held in the plastic), tip of the red plug is held with the left hand while black jack tip is held with the right hand.
- Paste the moment the two probes at the terminal 220v ac input transformer and then remove with fingers still attached to the metal tip of the AVO-meter probe.
- At the time of releasing the contact probe, it will be felt a shock or a small electric shock.
Where it comes from stress this surprise?, And we know that the AVO-meter uses only 3-volt battery voltage only.
In all inductors (coils) through which the DC current and then disconnected, then the flow will suddenly disappear. The current that disappeared abruptly with a very short time this will raise the voltage shock that time was very short so-called stress "induced self" (self-induction) on the coil itself. This self-induced voltage magnitude to several tens of times the voltage of DC origin. Self-induced voltage is what causes a shock when we measure the power supply transformer.
So that happened on the flyback transformer primary coil. Transformer current is passed through the shaped pulses on-off repeatedly with high frequency voltage shock that can generate up to tens of thousands of volts.
Resonant capacitor are used to "absorb" the shock of this high voltage by absorbing the voltage to charge the capacitor.
Therefore, if the resonant capacitor until loose solderannya or capacitance values fall, then the induced voltage from the flyback transformer does not have a mute. Tens of thousand volt electric shock will be received by the collector of transistor HOT causing transistor die instantly because it is not resistant.
If the resonant capacitor is damaged, but still hold the HOT transistor working up to several tens of seconds only, then it can cause:
The voltage output from the flyback, such as the heater, screen, anode voltage (HV) etc will rise.
If the aircraft is equipped with X-ray protector, the protector will actively work
Raster narrowed slightly left-right
Internal jump occurred in the high voltage flyback flyback which could damage itself, or damaging the internal high voltage capacitor is in the flyback.
There is a possibility of damaging the picture tube (arising stepping fire therein).
In normal conditions, when the transistor HOT work, there are 2 kinds of voltage received by the collector of transistor HOT.
DC voltage B +
Shaped voltage pulses of magnitude less than 10x the voltage B +. Therefore HOT transistor must withstand a minimum of work on the voltage 1500v.
If the value of resonant capacitor value is enlarged (plus the way diparalel for example), it will result in:
High-voltage anode drop
The speed of electron beam from cathode towards anode (screen) decreases, causing the brightness of the image also decreases.
Electron beam so much easier to be deflected by a deflection coil (yoke) so that the raster will expand more broadly, both vertical and horizontal.
2. Flyback short on primary coil
In normal conditions, when the transistor HOT on condition "on" then the current through the transistor size will be limited by the "inductive reactance" flyback primary coil. If the primary coil flyback short, then there is nothing that limits these currents, so the HOT transistor can die instantly.
Keruskan flyback at the secondary or damage to the deflection coil (yoke) horizontal well can menyebablan HOT transistor is broken, but generally do not cause instantaneous death.
How to prevent damage to transistor HOT died on the spot over and over?, Before replacing the HOT transistor, then do the examination as follows:
- Check solderan and resonant capacitor capacitance value. What is Multi-meter you have to to check the capacitors?
- Check if the flyback transformer primary coil is not short. examination of the flyback transformer primary coil can be used ESR-meter, so it does not have to bother to let go. Under normal conditions, the ESR-meter needle does not move.
- Check whether the deflection coil (yoke) horizontal section is not short. Check with the ESR meter such as checking the flyback transformer, so no longer need to remove it.
Another way to check if it does not have the ESR-meter or a capacitance-meter:
Provide a 100W light bulb and give more or less 2x20cm cable connection.
Disconnect the relationship between the pin-point with collector transistor flyback HOT.
HOT new transistor pairs.
Put the lamp between the flyback with collectors.
Turn on the plane. Lamp will light. Check if the voltage screen out (set the maximum screen VR)
If no screen voltage circuit means there is a problem, such as flyback damaged.
If the high screen voltage (200V more), the possibility of resonant capacitor defective
If the screen voltage of about 150v or less, probably no problem. Means it is safe to install HOT transistor.
Sumber :http://beteve.com/
Penulis : Sumarsono Budiharjo
Editor : Ashif
