AC Power line Problems

The environment around an electronic equipment can affect the way the equipment operates. An electronic equipment may be affected by radio interference and power-line problems in the “electronic environment”. Electronic equipments may also be affected by temperature, humidity, etc, in the “physical environment”. You might expect the power company to guarantee smooth, uninterrupted, electrical power. Unfortunately, the conditions in the power lines to your home or office are constantly changing. Power problems can be divided into two main category, that is:

• Overvoltage
• Undervoltage

Overvoltage

Overvoltage – can be again divided into two types, spikes and surges.

Spikes

A spikes is a very short burst of high voltage which can disrupt the operation of any electronic equipments. Some small spikes are caused by switching equipment, including motor controllers. When lighting strikes the power system, it can cause very large spikes.

The effect on electronic equipments varies with the size and power of the spike. A typical spike may have a fairly high voltage (5000 volts or more). Small spikes usually don’t damage the components, but spikes caused by lighting can be much more powerful. It can burn the complete PCB of any electronic equipments. As you are troubleshooting, whenever you notice that many parts are damaged, in different parts of the equipment, suspect lighting damage.

Surges

These are overvoltage that last for more than one cycle. Surges are caused when some heavy electrical load is suddenly switched off. Surges can cause damage in many equipments.

In case the overvoltage is very severe, it can slip through the power supply and can blow up the components inside the equipment. A continuous high voltage can damage the power supply itself.
Spikes and surges are generated by the switching off of high power motors and other inductive appliances. All electric motors and transformer generate fields that store energy. When one of these appliances is switched off, the magnetic field collapses and as a result the stored energy having no other place to go, come down the power line as a spike.

Relatively small motors like those used in refrigerators, photocopiers and air-conditioners can also lead to spikes of thousands of volts.

Spikes and surges damage any equipment on a cumulative nature. When a number of spikes and surges get through, first the component and then the electronic equipments fail. Spikes and surges are the main cause of destruction of the electronic equipments.

Undervoltage

Undervoltage – can be further divided into three categories, sags, brownout and blackout.

• Sags: Sags are undervoltage that last for more than one cycle. Sags can slow down the computer disk-drives, leading to data errors and can cause head crash making permanent data loss.
• Brownout: Brownout is the low voltage condition that can be present even for several hours. This is often created when the power demand exceeds the capacitor of the power generator. Brownout can also cause many problems. Fortunately, high or low voltage problems can be tackled by using some good quality voltage regulators.
• Blackout: Blackout is the complete no-power condition. Sometime sudden power failure can bring about wastage of time, money and resources.
  The interrupted process may have to be restarted from some earlier stages or sometimes even the complete work may have to be redone right from the beginning.
  

Noise

Any signal present on the power line besides the expected alternating current of 50 Hz is called the noise. Noise usually consists of short term over and under voltages. Any noise entering a computer brings about data errors. If the noise is strong enough, it can get past the power supply and create false digital “1s” and “0s” and can confuse the computer such as cause the computer to produce a bad bit of data. A few of the letters in a word-processing file may be incorrect, or some of the numbers in the spreadsheet may be wrong.
There are several different types of noise. Radio-frequency interference (RFI) is caused by radio or television sources, or even by other computer equipment. If your equipment is located near a radio or television transmitter, the power or signal lines may pick up enough of the radio or TV signal to cause problems. A weaker source, such as a wireless telephone, fluorescent lamp, lamp dimmer, or a car ignition system, can cause similar problems if it close enough to your equipment. Radio energy drops off very quickly as you move away from the source.

Electro magnetic interference (EMI) can occur when computer wiring runs too close to equipment that produces an electromagnetic field. As the magnetic field changes, it can “induce” false pulses into nearby computer wiring. Again, this effect drops off sharply as you move away from the source of the EMI. EMI can be a problem when two wires run beside each other. A signal in one wire can create a changing field, which then induces a signal in the other wire. The effect is stronger when the wires are close together and when they are parallel for a distance. Large electric motors can create powerful electromagnetic fields and may cause EMI problems. Electric motors, which may cause EMI, are found in various kind of equipment-refrigerators, air conditioners, washing machines, furnaces, copier, elevators, machine tools, and so on.

Harmonic Distortion

Harmonic distortion is the deviation of the power supply waveshape from a pure sinewave. It can disrupt the operation of some sensitive device like computers and communication equipments.

With Regards,

Sebastian

G.M. Technical

Nunes Instruments

645 Hundred Feet Road,

Coimbatore. 641012.

Tamil Nadu

India,

Web: www.nunesinstruments.com

Mail: info@nunesinstruments.com



Mobile: 09345226022

How to test Crystal?

Crystal are use to keep the frequency of the clock from drifting. If the signal from this clock stops, or is weak, or the pulses begin to vary, the electronic equipments might show intermittent faults or might stop altogether. The microprocessor pins that hold the crystal are usually called OSC IN and OSC OUT as shown in Figure 1 and the frequency is marked on the crystal. Typical examples of crystal oscillator frequency are 3.58MHZ, 4MHZ, 8MHZ, 24MHZ etc.

Testing Crystal

Crystals are quite fragile components because of their construction. Unlike a resistor or capacitor, if you drop one on the ground from a decent height, its 50-50 bet whether it will work again. Testing the crystal is not a breeze either. You cannot just take out your trusty multimeter and plug the crystal in it. In fact, there are three right ways to test a crystal.

• Using OscilloscopeA crystal produces a sine wave when excited. It is appropriate then, to see a waveform representative of a sine wave on the clock pins. If the clock is not functioning properly, replace the crystal. In most cases this should solve the problem since microprocessors are usually very reliable. Check the crystal with power on.


• Frequency Counter Frequency Counter can be use to check the frequency of the crystal. The reading must be taken when the equipment power is switch “on”. Place the probe of frequency counter to the crystal pin and read the measurement. Be sure that your frequency counter meter has the range that is higher than the crystal frequency you are measuring.


• Crystal CheckerWith this method, usually the crystal is placed in the feedback network of a transistor oscillator. If it oscillates and the LED is lighten up, this mean that the crystal is working. If the crystal doesn’t work, the LED stays off. Instead of using LED, some other crystal checker uses a panel meter to indicate if the crystal is working or not.
  You can download a free crystal project kit at:

www.cs.okanagan.bc.ca/ve7ouc/eng/kc6wdk-mirror/crystaltester.html

EEPROM

EEPROM stands for Electrical Erasable Programmable Read Only Memory and also referred to as E²PROM. As the name suggest, an EEPROM can be both erased and programmed with electrical pulses. Since it can be both electrically written into and electrically erased, the EEPROM can be rapidly programmed and erased in circuit for reprogramming without removing them from the circuit board.

EEPROM is also called a non-volatile memory because when power is turned off the stored data in the EEPROM will not be erased or intact. New EEPROM have no data in it and usually have to program with a programmer before it can be use. Information stored in this type of memory can be retained for many years without a steady power supply.

What is the function of EEPROM?EEPROMs are used to store user programmable information such as: -

• VCR programming information
• CD programming information
• Digital satellite receiver control data
• User information on various consumer products

EEPROM in monitor performs two functions

• When a monitor is switch on it will copies all data or information from the EEPROM to the microprocessor. For example, the EEPROM will let the microprocessor know the frequencies at which the monitor is going to operate.
• The EEPROM is used to store the current settings of the monitor. The settings of the monitor will not be erased even when the monitor is turned off. Anytime a change is made in the monitor settings, the microprocessor updates the setting in the EEPROM. When the monitor is turn on again, the stored settings are used to set up the monitor for operation.

What are the symptoms if the MONITOR or TV’s EEPROM data is corrupted or damaged?

• No high voltage (no display).
• Horizontal or vertical frequencies run.
• Cannot save (store) current setting.
• Certain control functions like sound, brightness and contrast control does not functioning.
• On Screen Display (OSD) does not function or the OSD have a corrupted display.
• High voltage shut down (EEPROM set the horizontal frequency way too low or twice the line frequency perhaps leading to failure of the horizontal output transistor (HOT)).

What is an EEPROM programmer or copier?

EEPROM seldom fail, they just lose or have their memory (data) corrupted may be due to high voltage and static discharge from a monitor. Once reprogrammed they are as good as new. As mentioned earlier, new EEPROMs are blank and need information or data to be loaded in order for it to functions. The job of copying the data into an EEPROM is done by a programmer or a copier. Programmers comes in all shapes and sizes. You can copy these devices for repair replacement only. You cannot copy them for resale without a letter of approved from the vendor who produced them. There is quite a number of companies selling EEPROM programmer.

For sourcing EEPROM visit http://www.nunesinstruments.com

What is ESR METER ?

All capacitors have a certain amount of resistance to the passage of AC current. ESR (Equivalent Series Resistance) is the sum of all internal resistances of a capacitor measured in Ohms. An ideal capacitor has ZERO ohms ESR.

Electrolytic Capacitors have a tendency to increase its ESR overtime due to drying or corrosion. High ESR is a frequent problem in today’s electronic circuit. Even a 1 or 2 ohms rise in ESR can cause complicated problems. Under normal conditions the ESR has a very low value, which stays that way for many years unless the rubber seal is defective, in which case the electrolyte’s water component gradually dries out and the ESR creeps up with time. The increase in ESR increases both voltage drops within the capacitor and the heat, produced in the capacitors due to resistive heating. If you don’t check for ESR, you may be in for a “TOUGH DOG” repair. High ESR is the first sign of a capacitor failure. High ESR will cause complete circuit failure, over heating of capacitor, loading of the circuit, overstressing of other circuit components and other undesirable effects.

Why should I use an ESR?

Because measuring an electrolytic capacitor with an analog or digital capacitance meter can MISLEAD a technician into believing that a defective capacitor is good. This can waste your precious time and you are unable to repair the equipment. Which means you can’t charge your customer! If you don’t test for ESR on the capacitor, you will always miss the bad capacitor. Normally, these bad capacitors have high ESR reading which your normal multimeter or digital capacitance meter can’t measure. Only by using the ESR meter, you will be able to measure the ESR on the capacitor and you will not be fooled by capacitors with bad ESR. ESR meter can even work IN-CIRCUIT, which means you don’thave to solder out the capacitor in order to measure it using normal capacitor tester, which would not be accurate anyway.

Do you know that ESR meters can perform other wonders besides checking the ESR of a capacitor?

Some digital ESR meter have the features of checking:

• Low ohms resistor such as 0.22 ohm, 0.33 ohm and etc.
• Horizontal yoke coil winding of a picture tube, inductor and primary winding of a transformer – If a shorted turn is present, the inductance drops dramatically and the meter will show the ohms reading.
• Horizontal output transistor (HOT) in a monitor or TV – If an open-circuit reading is obtained, the short-circuit is elsewhere. If the short-circuit remains, the transistor is faulty.
• Short-circuit in the track, usually trace to the components - You can use the ESR meter to locate short-circuits on printed circuit boards by measuring the actual track resistance. If the reading increases as you probe further along the track, you know you’re going in the wrong direction!
• Speakers, amplifier etc - The pulses have a fast rise/fall time, so it would probably make a crude RF signal injector as well.

The condition of both the normal and rechargeable batteries – Flat and faulty battery will have high ESR.

For Servicing and repairing of ESR meter and other instruments

Visit: http://www.nunesinstruments.com