Electronics Resistors

Electronics Project – Stopwatch

Author: admin

This is a second version of my last video – the clock. Calling it a stopwatch is a much more appropriate name. Integrated Circuits: – 1x 555 Timer Chip – 1x 7404 – 1x 7408 – 1x 7402 – 2x 74160 – 2x 4511 – 1x 7805 Voltage Regulator Other Components: – 2x 7-Segment Displays – 1x Green LED – 3x Capacitors – 19x Resistors – 1x Push Button

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Tags: Electronics, Meltdown, project:, Stopwatch, Tahiti
January 10th, 2012  |  Posted in Electronics Resistors  |  Comments Off

How To Restore Picture Tube Without application a crt tester, restorer or rejuvenator

Author: admin

Picture become weak or dim usually happen after the monitor have been used for many years. Again it depends on the quality of the picture tube or cathode ray tube (CRT). Some grade A CRT can last for many years, but for the lower grade one it can only last for couples of year. Don’t be surprise that I do come across picture tube that had gone dim in less than a year! If you switch on your monitor for 24 hours without turning it off, then expect the tube to become dim fast. Besides dim (weak emission) , CRT may also develop many problems such as open filament, short between cathode and heater, G1 and G2 short, poor gamma performance, stripped cathode and focus and G2 short. In this article, I’m going to touch on the weak emission problem only and show you a possible way to brighten up the picture tube.

The cathode ray determines the brightness and sharpness of a picture tube. Its electrons are emitted from the cathode surface into the cathode ray tube’s vacuum. The electrons then strike the screen in the form of a ray and cause it to shine. Weak or used up cathodes produce few electrons and emit weak electron rays. This causes the picture to become dark and fuzzy. Sometimes the cathode emission ceased due to a layer of contamination coating covers the cathode surface. This contamination prevents the electrons from leaving the cathode’s surface thus you get a dim picture.

In order to identify whether is the tube that cause the dim or from bad components, one can always use a CRT tester/meter to check it. Some call it CRT rejuvenator, CRT restorer and others named it as CRT regenerator. These testers are designed to test and check CRT and fix it if the picture tubes have problems. I personally owned two CRT testers- the BMR 2005 Muter regenerator and a less feature one I bought from Thailand. With the help of CRT tester, I can know if a picture tube is working or not. If you do not have one, don’t worry because by checking the voltage at the CRT socket pin outs, you will have some ideas if the CRT is good or bad.

From my experienced, I noticed that the older tube can be brightening up with the help of CRT tester but not for tubes that was made in the year 1994 and above. I suspect the getter (made of barium) inside the tube have been used up. The functions of getter inside the tube are to absorb gas that was release when the cathodes are heat up. If the getter fails to absorb the gas, then there is no point to restore a picture tube. I have brightened up many picture tubes with the help of CRT tester and some looks like a new tube. But somehow after one or two days the picture tube get dim again because the getter cannot absorb the gas and the gas will travels back to the cathode surface and turn it into carbonate. Electron emission will cease again. I even have tried some home made CRT restorer downloaded from the internet and the result is still the same-the picture tube will dim back after couples of days.

After done some research and experiment, I found that the best way to brighten up the tube is to increase the heater voltage. Normal heater or filament voltage is about 6.3 volt and if you increase the voltage to about 8 to 9 volts, this means the cathode will produce more electrons and thus the screen will become brighter. Bare in mind that do not apply any voltage that is higher than 9 volts to the heater otherwise the internal filament will burn out and broken. Once it is open then there will be no way to rescue it.

If the picture tube is heading to rubbish dump then there is no harm to try to restore it. About how long it will last, I cannot guarantee it. Some will last even more than two years and some only couples of weeks. Recently there was a badge of Compaq and Hp 15” monitor that have the symptom of blur display with bright picture. No matter how hard you try to adjust the focus adjustment at the back of flyback transformer, the picture still look slightly blurs. Using the methods above I had saved lots of picture tube (I don’t need to replace a second hand one to customer).

It is a simple modification and this only applies to the 14 and 15” monitor picture tube only. First you need to find which secondary output that have output from 12 to 15 volts. Once you have locate it, then solder a wire at the cathode pin of the diode and join it to the input pin of 7808 (output 8Volts) voltage regulator. Please don’t tap from the B+ voltage which is usually 45 volts and above and this may kill the 7808 IC because this IC can only withstand voltage up to 38 volts maximum. The current drawn from the 14 and 15” picture tube is less than the 17” tube and if you use this way to brighten up the 17” tube, the power supply may go into shutdown mode and sometimes will even lead to power blink.

I do know some technicians like to use the method of turning few rounds of wire at the flyback ferrite core to restore the brightness. This method can work in Television but not in Monitor. Computer monitors runs in many resolution and the higher the resolution the higher the B+ voltage and thus making the output voltage at the wire increased. This will lead to a sudden brightness and may shutdown the monitor. Even if it didn’t shutdown, the customer may get annoyed with the Monitor brightness (raster) whenever the customer change the monitor resolution.

Now solder the pin 2 of 7808 IC to cold ground and the output of 7808 IC pin 3 to the CRT heater point as shown in the picture. Remember to cut off the 6.3 volt supply line from the power supply because you don’t need it anymore. What you need is the 8 Volt supply to the filament in the picture tube. You can also connect a low ohm protection resistor in series to the heater point. Just in case if any short circuit happens the resistor will open circuit. Make sure you attach the 7808 IC to the heatsink, preferable the heatsink at the flyback transformer.

This method only work for tube that is slightly blur and not too dim picture. If a picture is very dim even if you raise the heater voltage to 12 volt, you still would not see a bright picture. As mentioned above there is no harm trying to modify it and who knows the tube can be brought to life and serve the customer for many years. Hope you enjoy the article.

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Tags: Advertising, application, Cannes, Festival, International, Picture, rejuvenator, Restore, restorer, tester, Winners, Without
January 7th, 2012  |  Posted in Electronics Resistors  |  Comments Off

Load Break Switch

Author: admin

In power applications, switches perform function to energize or unenergized an electric load. On the high end of the scale are load-break switches and disconnecting switches in power systems at the highest voltages (several hundred thousand volts).

Load-break switches are required to maintain the capability of interrupting the load current. The load break switch in a circuit with several hundred thousand volts, designed to carry a large amount of current without overheating the open position, having enough insulation to isolate the circuit in closed position, and equipped with arc interrupters to interrupt the load current.

Load break switches of air break are of versatile switch gear for transformer control & protection. They can also be used for Motor feeder in conjunction with Vacuum contactors. They are highly useful for Ring feeders for isolation of faulty section either manually or through remote control if fitted with motor operation. Load break switch in conjunction with HRC fuse can tackle high fault current and offer very good protection against dead short circuit capacity up to 40KA.The fault clearance and isolation through this combination will be achieved in a few milli seconds provided a proper selection of LBS and fuse is done. HRC fuses are manufactured with silver strips/silver coated Cu. Strips wires surrounded by granular quartz. When short-circuit occurs the metal element melts and the molten metal melts the surrounding quartz, making the combination an insulating material, called fulgarite. There will be a number of sections in the element which will create similar insulating media in quick succession and thus the arc will be extinguished in a matter of few milliseconds, say 5 to 8 milli-seconds, ie., less than 1/2 a cycle.

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Tags: Switch
January 1st, 2012  |  Posted in Electronics Resistors  |  Comments Off

Surface Mount Resistors

Author: admin

Surface mount passive electronic components are easily described as a flat chip with a terminal that is soldered onto the printed circuit board with no leads penetrating. Designed with size in mind, they are very small and amazingly reliable. Not only are they reliable, but these surface mount components are made to perform a variety of circuit functions. Surface mounting helped reduce labor costs and increase production rates with its high degree of automation. The main advantages of SMT over the older through-hole technique are: Lower resistance and inductance at the connection (leading to better performance for high frequency parts), Better mechanical performance under shake and vibration conditions, SMT parts generally cost less than through-hole parts.

An example would be a thick film resistor, with 1% resistance tolerance and with a low temperature coefficient. Less well-known is critical resistance, the value below which power dissipation limits the maximum permitted current, and above which the limit is applied voltage. The resistors are produced in a wide range of values from high resistance values to very low ohm. Size, and position of leads (or terminals), are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power.

Built to use in electronic labs, electronic design kits, are extremely convenient as they offer all values of resistance, inductance or capacitance for any engineers use in designing and developing circuits. Kits are supplied packaged in notebooks, cases, cabinets and bins and may be bulk components, on tape or on tape and reel. Garrett Electronics, an authorized distributor, builds these lab kits using components manufactured by their authorized lines. Kits are available with all standard values of 0402 1% SMD resistors, Garrett Electronics stocks and supplies, for same-day shipment, all standard values of 0201, 1% surface mount resistors on full reels, as partial reels or continuous tape, with leaders and tails ready for automatic pick and place equipment.

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Tags: (Resistors), Surface
December 29th, 2011  |  Posted in Electronics Resistors  |  Comments Off