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 JVC VCR Problems for Model HR-J321EM-No power

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hany_national
هانى النجار Professional Technician
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عدد المساهمات : 1314
تاريخ التسجيل : 14/11/2009
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الموقع : Egypt.Alexzandria

مُساهمةموضوع: JVC VCR Problems for Model HR-J321EM-No power   الثلاثاء نوفمبر 09, 2010 3:54 pm

JVC VCR Problems for Model HR-J321EM-No power

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]



A customer sent me a JVC HR-J312EM model VCR for repair. The complaint was no power. I personally don’t repair 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 repair it. Repairing VCR at my era actually has begun to go obsolete because of the market filled with VCD players.



VCD player is cheaper than VCR and compact in term of the size. Back then, many people sent their compact disc and laser disc players to electronic repair shop to convert 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.



[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]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 reason as to why the main filter capacitor still holding the charge.



By following the positive 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 reduce 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.



[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]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 become defective after in service for sometime. Replacements of the two resistors brought the VCR back to life again.



[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]






Conclusion, whether 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, suspect a defective start up resistors. However, certain electronic equipment 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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roshdy

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مُساهمةموضوع: رد: JVC VCR Problems for Model HR-J321EM-No power   الثلاثاء فبراير 15, 2011 9:13 pm

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