Cover Letter To A Staffing Agency

INTEGRATED CIRCUIT

We see the main board of a PC source, highlighting its main components as well as primary and secondary stage.

Primary
is relatively simple, we do an inspection and verify that it has no bad component with the naked eye, once this step and if we find appropriate to replace faulty components, but before to prove we do other measurements.

If the fuse is blown chances are: diode / rectifier bridge so the short or leakage proceed to lift a leg and verification. Can also be short one or more transistor / heat sink is mounted, lift and check them short or leak. You may also not blown fuse but have components such as leaking open devalued.

Check that there are no filters or dried inflated to prevent the correct startup of the source, eg the main filters (330mf 200v) are pouring their liquid damage. We also have a polyester capacitor (Fig. 1 right at the bottom) that if this were their values \u200b\u200bor dry does not start the video.

Another cause may be resistance cut off value or proceed to verify especially those who have already taken a dark .

Remember to put a 100W lamp in series with the source before each test!

Secondary

First of all check as we said we have no inflation capacitor, diode, transistor resistance or black or burning, not to say that this is the ultimate failure and another component may have burned the same.

This is like in the previous stage we proceed to verify the components and any repair, but there are components that tend to fail more often. Check
diodes shaped transistor mounted on the sink, they tend to be short. Failure often results in the cranking power but you hear a scream and protected. Check

stage transistors, which are not on the run or short.
as 1N4148 diodes are very delicate and is likely to be put on short or remain open.

dry or bloated capacitors are usually one of the probable causes and failure result similar to (diodes mounted on heat sink) generally tend to fail the filter capacitors in stage +12, +5 approximately 2200mf 10v , 1000m 16v
That would be the way to repair without oscilloscope now we need one of at least 20MHz for to analyze more thoroughly the most frequent failures.

The integrated circuit 494 or 7500

494 in the IC must record the following Pata 12 = 13v power with power off is needed to feed himself in the leg 4 = 3.4vy when you start 0v

is convenient 13v power is integrated with the leg 12 and ground. Careful, do not connect the power to 220V, with that we would also be feeding the LM339 integrated

Source Start

I will give a brief but accurate explanation of the time which starts the fuente.Estos two LM339 integrated and 494 as we always say is powered by 13v while the PC is off, when you press the power button on the PC makes the mother earth (PS) which is the green power cable, which in turn drops the tension in the leg 6 of the LM339 3v 1g, then the leg 2 that had 3.6V drops to 0V while the leg 4 of 494, making the source starts, of course if there is no anomaly.

main legs 494 and their measurements

The Leg 5 of the 494 is the oscillator that forms a capacitor 1NF (102). With an oscilloscope waveform record a sawtooth, fig2. Thus we see that the integrator is oscillating.




With SP mass in the leg 8 and leg mass or mass 11 and recorded a square wave Deveria, Fig.3 if one pin is not recorded that way surely this damaged liver Deveria IC leg and check again, replace the IC antenna to verify that the damage is not caused by another component.

Each leg (8 and 11) forms an identical circuit, a 2.7-k R which is connected to V + NPN transistor (C945) and a diode, repeat the circuit is identical in the leg 8 and 11, if we measure the collector (C) of these transistors should see the waveform of Fig.4, verifying that this phase transistors working properly and not damaged.

Now if we follow the trail of the collector of the transistor will see that it is connected to a transformer, what we could do is to test on the primary side of the source taken as the negative mass main capacitors of the source and the transformer, the waveform Registering the