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
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).
Author CRT Television repair Course
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.ReplyDelete
Best Regards Humphrey.
Hi Jorge, Thanks for the info, i am equally excited to hear the outcome of this repair.ReplyDelete
That was interesting solution.ReplyDelete
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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.
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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...ReplyDelete
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.Delete
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Hi Michael, standby symptoms can be caused by so many things, but dry joints and capacitor with high esr are the main suspect.Delete
very well said sirs, but can you give me some clues on how to find protection ciurcuit of tv'sReplyDelete
Hi Salonga, you can get that using a schematic diagram of the same tV modelDelete
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useful answer in all question...ReplyDelete