How To Restore A 17" Monitor CRT Picture Tube

The 1st element of the write-up talked about about how you can faucet from the secondary diode to get the drive output as a result of the 7808 voltage regulator. The weak point of this circuit is that it are not able to electric power up the 17″ Watch since the electric power offer have some limitation in offering present to the more substantial CRT tube. The electric power offer will possibly shut alone off or electric power blink. In buy to counter this dilemma, we have to faucet voltage from some other sites in the Watch. Sadly there have been no far more sites (level) in the Watch in which you can faucet the voltage to electric power up the more substantial CRT tube. Owing to we could not identify the level then we have to produce (style and design) our individual circuit. The greatest is to use the Watch flyback transformer ferrite main and with wire loop all-around the main will make substantial pulse ac. This substantial pulse ac are not able to be evaluate by your typical meter.

With number of turning at the main (exterior loop), you can get a greater ac output voltage to electric power up the CRT heater. This technique only applies if you want to brighten up a Tv photo tube. You are not able to use this way on Watch CRT since as talked about before in the 1st element of the write-up, Watch operates on diverse resolution. The greater the resolution, the greater the B+ voltage offer to the principal winding of the flyback transformer. The greater the B+ voltage, the increased is the voltage output at the secondary aspect earning the output voltage (ac) developed by the exterior loop even greater. Therefore this will make a unexpected maximize in the filament voltage triggering an quick vivid in the Watch raster. Some check intended will shutdown if it detect a unexpected brightness in the raster.

Even if the check did not shutdown and if the person make your mind up to decrease the Watch resolution, the raster will instantly grow to be much too dim owing to decrease B+ voltage. You may well request you why computer system Watch has its individual six.three vdc output and why not like Tv set, the heater voltage arrives from the secondary winding of Tv set flyback transformer? The respond to is since the Watch designer wishes a continuous six.three volt for filament and never want the raster to be impacted by a shifting in Watch resolution. In buy to clear up this dilemma, right after earning about seven to 10 loops all-around the flyback transformer main, you have to transform this substantial pulse ac into DC voltage. You are not able to only use any diodes for this function. A basic function diode like the well-known 1N5401-1N5408 would not be in a position to operate in this circuit. The substantial pulse ac voltage will instantly destroy the diode as soon as the Watch is switched “on”. You have to use an extremely quickly restoration diode to do the task.

For your information and facts, not all extremely quickly restoration diode can proficiently operate on this circuit. You have to pick out the diode kind that has a speedier pace time like a 50 nanosecond and under. I experienced attempted a 75 nanosecond extremely quickly restoration diode and it blown at 800 by 600 resolutions but operate nicely in the 640 by 480 resolution. Following carried out some R &amp D, I observed that the greatest element selection to use is the UF5404. This diode has the specification of 400V, 3A and 50ns. When you have related the ac voltage to the diode, you now have to use a filter capacitor to filter off the ripple. You can use a price of 220 to 1000 microfarad 50V. Evaluate the output DC voltage and make certain it will have to have about at minimum 15 to 20 more than volts just before you solder to pin one of 7808 voltage regulatorYou can also attempt to use a 7809 if the exhibit is not vivid more than enough. Will not use any voltage regulator that is greater than 7809 usually the heater filament will get much too very hot and burn off.

Pin three of the voltage regulator is the output and it will have to joint to the heater pin at the CRT board as proven in the image. Cautiously location all the wires in a strategic spot and connect the voltage regulator at the warmth sink beside the flyback transformer. You are now prepared to change on the Watch and test if there is enhancement in the exhibit. If it ok then burn off in examination the Watch for partners of times to test if the exhibit is continue to vivid and crystal clear. If you are not contented with the sharpness, you can attempt to maximize a further volt by shifting the voltage regulator element selection to 7809. Some professionals favor to use a variable voltage regulator this kind of as the LM317T with a variable resistor so that they can modify to the drive voltage. If the photo tube is continue to dim and no way that you can boost the exhibit, I guess the time is up for the CRT tube. You possibly substitute a utilised tube or return the Watch back again to the purchaser. I hope you appreciate looking at this write-up. If so, make sure you truly feel free of charge to share this write-up with your pals or only ahead this write-up to any one you desire! You can find no restrict on the selection of people today you can share this with!If you have a problem or remark about everything in this write-up, fall me an e mail. Your comments is welcome!

Jestine Yong

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