Inspection method for monitor power supply by lightning strike _ hardware Maintenance

Fault model: Gold Great Wall c-i5271-type display;

Fault reason: lightning;

Failure phenomenon: no display. Users reflect that the machine was struck by lightning, issued a "bang" a sound.

Analysis and overhaul: Open the chassis found that the power fuse (f901/3.15a) has been burned, and the internal blackening, indicating that the power supply has a serious short-circuit failure. The power supply adjustment tube drain electrode (D) to ground resistance is 0ω, the gate (G) ground resistance is also 0ω, indicating that the power regulator has been completely penetrated.

The Power Regulator (IRFBC40) is removed from the circuit, with a three-gauge (MF-47 type) x1kω the resistance between D, S, G three electrodes found, has been completely short circuit. The value of the ground resistance of the connected circuit of the x1kω, x100ω and G three electrodes are measured by the ^50030401a^ table one, and the positive and negative resistance of G-polar is obviously abnormal according to the previous maintenance experience.

Check the power adjustment tube connected circuit (^50030401e^1), drain electrode (D) to connect the Power pulse transformer, the source pole (S) through the 0.2ω resistor to the ground, and adjust the pipe gate (G) through the diode D910 (byt42-m) to the ground. The diode D910 is removed from the circuit by removing a pin, and the positive and negative resistance is 5 Ω, indicating that the D910 has been penetrated.

The power supply of the machine is composed of current-type PWM circuit uc3842b and MOS tube (power regulator) IRFBC40, when the power-regulating tube is penetrated, the uc3842b is damaged under normal circumstances. Check uc3842b the different pin to ground resistance found no obvious anomaly. Check the uc3842b offline status of the DC resistance between the pins and the uc3842b check, are in accordance with the normal values in table two (normal resistance see ^50030401b^ table two, ^50030401c^ Table III is the uc3842b of the typical voltage parameter values). Check the other parts of the power supply circuit also did not find short-circuit phenomenon.

Replace the power adjustment tube, diode D910, fuse F901. In order to prevent the power supply short circuit (especially the line scanning circuit short-circuit), the +80v output of the line scanning circuit is disconnected, from the power output end of a 40w/220v bulb, the power-on, monitor power supply indicator light, indicating power short circuit fault is excluded. The test field scanning circuit power supply +50v, the digital circuit +15v, the control circuit +25v, the video amplifying circuit +80v all is normal.

Detection of line scanning circuit, CRT circuit, etc., no obvious open circuit or short-circuit fault, remove the light bulb, the line scanning circuit of the +80v connected, boot again, monitor power indicator light, indicating line scan circuit or line output circuit normal. The measured output tube set electrode +80v Normal, then +50v, +15v, +25v and +80v were all normal. Turn on the host, add the signal, display the monitor. Through the host to change the display refresh rate, change the display mode and screen brightness, contrast and other items to adjust all normal, continuous boot two hours without problems, indicating that the fault of the monitor has been excluded.

Summary: 1. The display is struck by lightning, which often causes extensive damage to the circuit, especially power circuit, line scan, field scanning circuit and interface circuit with the host. This monitor is struck by lightning, there is a "bang" a sound, the general description of the power supply has a serious short-circuit fault, the focus should be placed on the power supply circuit. Because there is no law to follow the lightning, but also do not know that the fault may be part of the circuit, so we should establish a correct way to determine the fault area. Because in the general display power circuit, the protection circuit is more complete, when the power supply (scanning circuit, etc.) circuit appears short-circuit or open, can get good protection, power circuit will stop working, no output voltage, power supply fuse will not burn. If a power fuse is found to burn, the fault should be in the power supply circuit itself. Starting from this idea, first of all, check the power supply circuit, which can quickly check the location of the fault.

2. When the lightning instantaneous into the machine, its powerful pulse current will be in the power supply impulse transformer generated instantaneous strong reverse induction pulse voltage, because this pulse voltage is far greater than the power regulator of the reverse breakdown voltage, resulting in the power of the adjustment tube reverse breakdown, so that the power fuse burned.

3. Because the power supply circuit of the monitor is switching power supply, power supply can not open the load, check the fault of the power supply circuit and scanning circuit, should be the power output (high voltage output) after a false load, the general use of light bulbs, the size of the lamp should be based on the display power output voltage or power load size to determine, 14-inch ~17-inch displays generally use 40w~60w/220v bulbs.

4. Under normal circumstances, when the user set the power to open the display mode, is to sync with the system (WIN95/98), that is, when the host power off, the Monitor's power will also be turned off, but at this time is a soft shutdown, although the power off, the power switch is not really disconnected, still remain closed state, Thus the conditions are provided for the channeling of lightning or other strong pulse disturbances. It is recommended to develop a good habit: Each shutdown, the host, monitor the power switch disconnected. If you are accustomed to the use of soft shutdown, the total power should be shut down, you can avoid a lot of unnecessary trouble.

5. Because the IRFBC40 is difficult to buy after the damage, it can be directly substituted by irfbc40a and irfbc80a, or it can be directly substituted by 6n60. The performance parameters of IRFBC40 are shown in table four of ^50030401d^.