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Re: sanyo dp42746 low volt power problems
The power supply is failing, or there is another circuit area that is pulling too much current, and the supply is going in to protect mode.
This would require proper troubleshooting by an experienced tech. If the problem is very involved, or the tech is not familiar with the set, he will require the service manuals and service information.
a 6ya Technician can help you resolve that issue over the phone in a minute or two.
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If you do not already know where your problem is then Check for 12 volts DC (AC-off detect) at pin 3 of PC9A21, if missing replace PC9A21 part # 268P058020 on the Power PCB. LED does not blink at plug in. Check for 5-volts DC at connector RF pin 3 (system reset) if low or missing suspect the reset switch S7L20 part # 432P089010 on the Control PCB. LED stops blinking after 70 seconds of plug in but will not power on. This model is equipped with a keyboard lock feature; this can be mistaken as a no power condition. To unlock the keyboard press and hold the "menu" button on the front panel for 10 seconds . LED stops blinking after 70 seconds of plug in but will not power on. Check for 4.7 volts DC at connector RF pin 4 and 5 on the Signal PCB if low suspect problems with the switches/buttons on the Control PCB part # 935D587002 5. LED stops blinking after 70 seconds of plug in but will not power on. Keyboard is not locked and key inputs at connector RF pin 4 and 5 check good suspect the E2P PCB part # 935C978002 . Also if you can do a self diagnosis test by pressing the device and menu for 5 sec on panel of set and read the error codes.
Check and replace the damaged component/s at its main board. Contact any service technician. If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
These blinks [flashes] are fault indication (Error Codes).From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it.This will make repair easy.These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times.Count it carefully.If you wish to get some details, check the site linked here.It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices.Viewing it in "Mosaic" or "Magazine" will make surf easy. http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given.Surf the site with patience.
Power LED blinking it about 90% power supply board is dead.The other 5% are both boards some time are dead.The power supply board and the Tuner siginal board is dead.Replaced the power supply board it ur best bet to get power back.After power is back should get picture too.Not than the Tuner board also need it replaced.Tries Websites Shopjimmy.com,Ebay.com for boards parts.
So the 12V power supply is either not there (faulty power board) or is shorted by whichever board it is passed to.
I do not know this particual Sanyo, but I know what I'd do - I'd open and see at the power board which of the output cables carries 12V; they are most commonly labelled on the power board, right next to the output pins.
12V is usually power going to the audio amplifier and sometimes to tcon (LCD controller) of even the main board , but it won't go to to the ysustain - the other apparently large board when you open the TV.
Of all listed I'd say only the audio amplifier is likely to short...all others are possible, but highly unlikely.
BTW what do you mean "but turns off, when back is removed"?
to test all y sub boards remove the main power connection to the y main and turn the tv on if it powers on one of those boards are bad.. remove both sub boards. and plug in the y main. if it powers on then that board is good either, put your multimeter on 2k omh and test the upper ysub boards black connector, the top 2 pins with negative to the 5th pin positive. you should read 500-1k ohm if its way under 100 there is a short.
the bottom ysub board place the multimeters black probe on the bottom 2 pins of the black power conection and the red on the 4th pin.. results are the same.
1. Check for no 8.4 volts DC at pin 3 of PC9A10 on the Power PCB, if low or missing replace PC9A10 part # 268P058020. 2. LED does not blink at plug in. Check for 3.3-volts DC at connector RF pin 3 (system reset) if low or missing suspect the reset switch S7L20 part # 432P109010 on the Control PCB. 3. LED does not stop blinking after plug in. Verify the standby supplies, 12-volts at connector KA pin 17, 6-volts at KA pin 18 and the 28-volts at KA pin 19, if the supplies are present suspect the DM PCB part # 934C067002 4. LED does not stop blinking after plug in. Check C9B01, C9B02, C9B10, and C9B11 (1000 UFD 16) on the DM PCB, if they are bad replace them with part # 181P734030 (680 UFD 16 V). 5. LED stops blinking after 70 seconds of plug in but will not power on. This model is equipped with a keyboard lock feature; this can be mistaken as a no power condition. To unlock the keyboard press and hold the "menu" button on the front panel for 10 seconds 6. LED stops blinking after 70 seconds of plug in but will not power on. Check for 3.2 volts DC at connector RF pin 4 and 5 on the Signal PCB if low suspect problems with the switches/buttons on the Control PCB part # 935D736001 7. LED stops blinking after 70 seconds of plug in but will not power on. Keyboard is not locked and key inputs at connector RF pin 4 and 5 check good suspect the E2P PCB part # 934C061001