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Sharp LC60C7500U not powering on/led indicator not showing in standby


I have a Sharp LC60C7500U 60" TV which does not appear to be powering on. When pressing the power button the LCD does not light up and the indicator light on the bottom of the TV does not light up even in standby.

First I checked the voltage at the fuse right after the AC connector. From neutral on the AC input connector to the fuse we see around 122 V.

Checking the connector hooked to the power drive which splits out to the other boards I found the following voltages with the 1st reading starting at the PD label

48.9, 48.9, 48.9, 48.8, 48.9, 48.9, 48.9, 49.0, 49.0, 49.0, 49.0, 49.0

Looking specifically at the LED indicator board it appears the board gets power, ground, and possibly other signals from the main board. Checking the input connector which is fed from the power drive board to the main board I found the following volatages reading from right to left on the connector.

8.9, 6.8, 48.7, 48.7, 48.8, 48.9, 48.9, 48.9, 48.9, 48.9, 48.8, 48.8

And for completeness I also measured the input connector on the LCD controllor board fed from the power drive. Reading pins from right to left I found the following

48.8, 48.8, 48.9, 48.9

Based on this I am under the impression this is not a power issue/issue with the power drive as it appears to be pushing voltage to each of the boards (Main/LCD).

Since the indicator LED is not showing even on standby and the entire TV does not appear to "turn on" when pressing the power button this leads me to believe this may either be two issues (LED indicator and LCD) or an issue isolated to the main board. But I'm unsure if these voltages are expected, if I performed the measurements correctly, etc.

A few questions based on this

  • Is it correct to take measurements on the connector pins using the neutral of the input AC as "commond ground"?
  • Has anyone had experience with Sharp TV's and possibly this particular model or close to this model to offer some feedback?

For reference here is the document I used which includes some block diagrams and wiring schematics.

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The PD connector on the power board has 24 pins (2 rows of 12 pins, odd numbered pins in one row, even numbered pins in the other) so you need to check what voltage is on pin 24 i.e. the STB (standby) voltage. It's is hard to access at either end as it appears on PD 24 of the mainboard as well. - see image below. You may have to remove the cable at the power board end and then check the voltage on the pin. Be careful that you don't short it out to another pin with the meter probe. The pin numbering is shown on the boards next to the connector

The STB voltage is usually about 5V DC. This voltage is used to signal the mainboard that the power is available and it is the mainboard that turns on the red standby power LED.

Block Image

(click on image to enlarge)

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Josh Schweigert zal eeuwig dankbaar zijn.

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