Monday, January 9, 2012

Sharp CRT TV Model # 21V1-L the power LED turns on but nothing else happens-email support



Hello Humphrey!

This is Juan Rash from Belize again asking you for help on TV repair.

I am trying to repair a Sharp CRT TV Model # 21V1-L. The power LED turns on but nothing else happens.


Is the power LED ON green? If yes then it means the power is doing well and the micro processor is being powered.

There is a voltage regulator IC with 4 pins on the secondary side of the board. This is the first time I am dealing with this kind of regulator. The part number is KIA78R05PI. 
Pin 1 is getting good voltage from the SMPS transformer but there is no output voltage on pin 2. 
Pin 4 is marked SW but there is no voltage on this pin. 

Pin 4 is the control pin or switch as you have rightly put it, when things are normal it should be around 5 volts. Now what can cause this voltage to disappear? This could mean there is a problem elsewhere like over current or overheating, so check for any shorted component on the secondary side of the supply…by the way is the H.O.T ok?

I want to know if Pin 4 is output or input terminal. I want to know if pin 4 need to get voltage to turn on the regulator.  The data sheet does not explain this part. 
Pin 2 and pin 4 go to the large IC. 

Pin 4 is the control pin, 5 volts normal ON and Zero volts OFF; as I have said this voltage can go low if the I.C is in protection mode

Thank you very much for your help!

Most welcome Juan.
Last but the least Juan always when you do a repair on TV and everything seems ok  and still the set appear dead, then try to power  ON the set using remote control power on button because sometimes the TV can be ok but be in standby mode.
Let me know how your are progressing on this
Regards Humphrey

Conclusion
From what Mr. Juan has said that it is his first time to deal with this I.C KIA78R05PI I feel I should highlight a little about this I.C for other tech out there, the best place to start is checking for the datasheet of the same I.C for assistance.
I checked this I.C on the internet and this is what I got, in our case the internal structure of this I.C will give us some insight about this I.C.


From the diagram about we see pin 1 (Voltage In) is connected to Pin 2 (Voltage out) via PNP transistor (you can actually call it a switch).

If Voltage is applied to pin 4 it will move to the Base of the NPN transistor inside this IC. Once the voltage get at the base of this transistor it will cause this NPN transistor to Close, This will then take the base of the top transistor(PNP) to the ground and then voltage will appear at  Pin2(Vo).

Humphrey Kimathi
Author CRT Television repair Course

13 comments:

  1. Hello Juan if you need you Can see the service manual here: http://www.scribd.com/doc/77636460/Sharp-21V1-L-Chasis-GA8. Lets see how this one turns out. I get this type of TV a lot here in Stann Creek too.

    Best Regards Humphrey.

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  2. Hi Jorge, Thanks for the info, i am equally excited to hear the outcome of this repair.

    Regards Humphrey

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  3. I would like to thank you for the efforts you have put in writing this website. I'm hoping the same high-grade website post from you in the upcoming as well. Actually your creative writing abilities has inspired me to get my own website now. Really the blogging is spreading its wings quickly. Your write up is a good example of it.
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    ReplyDelete
    Replies
    1. Hi Timothy,
      Thank you for words of encouragement Timothy,Here at Hum tech electronics we are committed to provide consistently high quality services to meet our consumer expectations at all time. on the side of getting your own blog..all the best from my desk.
      Kind regards
      Humphrey

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  4. Nice post. I was checking constantly this blog and I'm impressed! Extremely helpful info specifically the last part :) I care for such information much. I was looking for this particular information for a long time. Thank you and good luck.
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    ReplyDelete
    Replies
    1. Hi Jeffrey,
      Thank you Jeffrey for your positive feedback, Glad to note that you have found the materials on this site valuable.

      Wishing you the best in life

      Kind regards
      Humphrey

      Delete
  5. Hello there. My TV can't turn on..... when i switch it on, the red LED in front emit light but the TV Screen can't show anything - I'd really appreciate for any help - My TV is of Sharp brand...

    Thanks...

    ReplyDelete
    Replies
    1. This info is not enough for me to make any serious conclusion, try to power it up using remoter control, maybe it is just asleep. or press the front buttons one by one and see if it will wake up.
      Regards Humphrey

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  6. please,Help!My sharp color TV 14R2 switches on and switch off to standby mode and refuses to switch on again.What could be the fault.

    ReplyDelete
    Replies
    1. Hi Michael, standby symptoms can be caused by so many things, but dry joints and capacitor with high esr are the main suspect.
      Regards Humphrey

      Delete
  7. very well said sirs, but can you give me some clues on how to find protection ciurcuit of tv's

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    Replies
    1. Hi Salonga, you can get that using a schematic diagram of the same tV model
      Regards Humphrey

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