Samsung LN40B640R3FXZA Will not turn on

[maddog80]

My Samsung will not turn on, just a solid red light at the power button on panel. I tried pulling plug to reset, nothing. There is no clicking when trying to power on on the tv panel. I opened it up and there are no blown/bulging caps. I am considering replacing the main board. I do not have access to a meter to test the power board. Is replacing the main board a good start?

[tom66]

Re: Samsung LN40B640R3FXZA Will not turn on

Can you post some pictures of the overall circuit board layout of the set? Main board failure on this set is common, but other faults exist, too.

[budm]

Re: Samsung LN40B640R3FXZA Will not turn on

Also the P/N of the power supply board, I.E. BNXX-XXXXX.

[maddog80]

Re: Samsung LN40B640R3FXZA Will not turn on

See pics. Also the P/N for power board is BN44-00264A. The main board is BN41-01149B.

[selldoor]

Re: Samsung LN40B640R3FXZA Will not turn on

Without a meter even simple tests on secondary fuses are out.
Even cheapo 5-10$ would do.

[budm]

Re: Samsung LN40B640R3FXZA Will not turn on

OK, the power supply-inverter board has built-in pull up resistors for the PS_ON and the BL_ON, so disconnect the cable between the power supply and the main board, the backlights should come on when you APPLY 120VAC to the TV.

[maddog80]

Re: Samsung LN40B640R3FXZA Will not turn on

Disconnected the main board from the power board and the backlights came on.

[tom66]

Re: Samsung LN40B640R3FXZA Will not turn on

probably a bad main board -- need DMM to confirm.

[maddog80]

Re: Samsung LN40B640R3FXZA Will not turn on

I will get my hands on a multimeter. Once I get it, where should I test on the board to confirm?

[maddog80]

Re: Samsung LN40B640R3FXZA Will not turn on

I got my hands on a Fluke MM tester. Where should I start on the main board?

[tom66]

Re: Samsung LN40B640R3FXZA Will not turn on

First, check the power supply output voltages - 13V and ~5.4V - are OK.

To do this, place your probe on the pin corresponding to that voltage with the connector out. (TV powered on - backlight working. Do not touch any part of power board!) Note voltages.

Then, turn power off, plug in main board connector, and check voltages again in a similar manner. (Press probe onto join where sheath and wire meet, it's a few mm in.) Note voltages.

[Xecuter]

Re: Samsung LN40B640R3FXZA Will not turn on

My LN46B630N1FUZA has the same main board.

Anyone know what components are at fault?

[Dang]

Re: Samsung LN40B640R3FXZA Will not turn on

I do believe a shorted T-con could also stop the Tv from switching on, I would hook it all back up again but this time disconnecting the T-con from the main board(it's the board sitting at the bottom), see if it powers up after doing so.