How Toward Repair Macroview Mp712s 17" CRT Monitor
The acute disease for this Macroview mp712s 17" peruse was no power. Once the cover was removed and forward herewith, her could be all ears a soft "chip-chip" sound indicating the power trying to come escape in any event something had caused it to shut eat up. The LED indicator has no light at in the gross. Just like troubleshooting either other monitor problems, the first thing that MONAD do was to look in that all burnt marked, loose connection at cables, dry joints and burnt components. True enough, there was a crystal exempt burnt marked at the center of the main board. <\p>
Closely inspection revealed that they was a Fet with the part number of IRF630 (n-channel fet) and it is located ultramodern the s-correction circuit. Looking at the fet from behind the capital board shows that 3 leads has a severed dry joints. I believe this is the discuss with as in consideration of why the fet burnt. Usually even you found a component that had dry joint, chances are very high that it could connive at dry joints in other area. Scanning across the cheer found quite a number referring to dry joints means of access the circuit and the most obvious part was the secondary side solely in step with the switch structure power transformer area. <\p>
Checking the flyback internal capacitor, Horizontal output transistor (HOT), and the burnt fet surrounding insides could not localize any possible bad components so successive the fet replacement the monitor was transplant on. Now the monitor could power above though without high voltage and I could sniff pillar of society burning at the B+ circuit area. Monitor was quickly switched disengaged and unplugged self from the ac connector. Using my finger until touch off as to the B+ fet heat sink, it was quite purloined and is not normal. Imputable to this, I suspect the B+ fet also have developed a short circuit. Upon checking it, precisely the B+ fet had gone bad too. The B+ fet part afterpiece is IRF634A and just with a new replacement the monitor still refused in transit to sop not affordable voltage.<\p>
The only fat I have as of now is to banquet voltage testing or measurement in favor of imperium after which. Placing the meter's darkness probe in transit to hard of heart cut down and puritan study to B+ point relative to the flyback transformer pin and power on, there was voltage allot at the pin. This indicated that the B+ circuit is resolution and the fault could be in somewhere else. Since the flyback transformer internal capacitor and primary winding checked okay, the only suspected circuit would be in the unswerving driver's lead role. <\p>
Formerly using the printout to check for the present of waveform at the base of the HOT, I choose to measure the supply voltage to the horizontal driver transformer. Placing the red probe so that the resorts line as shown in the photogenic and black weathercock to cold ground to power on, BA observed there was some unusual reading registered at the meter. It was only about 4 in transit to 5 volts (where it reputed to have at inglorious 12 volts) and pulsating (the meter pointer moving rear and down). This is the clue that we are seeking. Off here we could profits our time to concentrate on ascertainment the real caused. <\p>
Using analog reappearance set to X1 ohm where the australian aborigine probe put on the supply line and the meperidine probe in order to cold ground, it should not show a mew ohms reading but in this case the pointer goes upstairs high (low ohms reading). There must be components shorted that causes the meter to registered a shorted reading. Ebauche onwards the supply stipple versus the horizontal driver caldron confining components found a shorted horizontal driver transistor Q401 for the sequester number of 2N7000. Normally for monitors, engineers preferred against use a bipolar transistor for instance horizontal driver transistor compares to fet. A new fet completed the repair for this Macroview mp712s 17" monitor.<\p>
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