A buyer sent me a Jvc Hr-J312Em model Vcr for repair. The complaint was no power. I personally don't heal Vcr because I'm more on computer monitor repair. Because of he is a friend of mine; I told him that I'm willing to take the challenge to heal it. Repairing Vcr at my era categorically has begun to go obsolete because of the shop filled with Vcd players. Vcd player is cheaper than Vcr and contract in term of the size. Back then, many habitancy sent their contract disc and laser disc players to electronic heal shop to turn the players into Vcd player.
What the technicians do was to add in a mpeg or Vcd card and tapped the Efm Rf signal from the Dsp ic. When you buy the Vcd card, it came along with a list of the Dsp ic part numbers and pin out and shown you at where you suppose to tap the signal. It was a 15- 20 minutes job and you could earn a lot from it. But now, everyone is using Dvd player and Vcd already obsolete.
Come back to the Vcr player, after opened up the casing and placed my probe on the two pins of the main filter capacitor, I could see the capacitor still holding the charge. If the voltage present at the capacitor pins, this tells us that the main ac voltage is coming in, the fuse and the bridge rectifier is working. There must be a surmise as to why the main filter capacitor still holding the charge. By following the inescapable marking pin of the main filter capacitor, I traced the line circuit and saw two high ohms resistors connected in series.
These two resistors are called start up resistors. The function of the start up resistors is to sacrifice the dc voltage to a lower value where it can then be supplied to the oscillator circuit and switch the power fet. If either one of the start up resistor developed an open circuit, there would be no supply voltage to the oscillator circuit and the power fet would not switch. Therefore no ac voltage produced at the secondary side of the power supply.
For the above Vcr, I found a start up resistor (220 kilo ohms) open circuit and causing no power symptom. Other components such as the power fet, filter capacitor and diodes found to be in good condition. For your information, if either one of the start up resistor spoilt, you have to replace both otherwise the other one would come to be defective after in assistance for sometime. Replacements of the two resistors brought the Vcr back to life again.
Conclusion, either you are repairing the Jvc Hr-J312Em model Vcr or any kind of electronic equipment, if you came across the main filter capacitor still holding the charge even with power off, surmise a defective start up resistors. However, inescapable electronic tool power supply designed, the capacitor may still hold charge even the start up resistors seems to be working. In this case you have to use other troubleshooting techniques to solve it. Please refer back to my website for more electronic troubleshooting tips.
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