Toshiba 49l621u BL_ON to DIM jump repair

[RainStorm]

I just got this TV in today, and originally it would flash the logo and have no backlight afterwards. I could see the image without the backlight with a flashlight.

Having no 9V batteries or anything on hand, and all the backlight LEDs looking fine during the flash, I decided to jump BL_ON and DIM on the power board/mainboard (White and purple wire) with them still plugged in using some scissors to connect my shielded voltmeter cables.

After jumping a few times, the backlight stayed on. Why?

I didn't measure any voltages beforehand... So just wondering what component does that. Mainboard or power board?

Its now all back together, and just wondering if I could get some insight. I would normally have baked the mainboard and powerboard if it came down to it, I didnt notice any loose solder joints though like I've seen on vizios.

TIA

[neilc6]

Re: Toshiba 49l621u BL_ON to DIM jump repair

Flash of backlights is a symptom of bad backlights and they should be all replaced with new strips. In Toshibas, bad backlights can damage the power supply. The LED controller circuitry shuts down the backlights if the wrong voltage is detected. Failing LEDs can have fluctuating voltages. DIM signal is typically PWM and by wiring to a high signal, they are likely at maximum brightness.

BGA failures affect Vizio M series and LG LE, LV, LW, and LS series. Do not randomly bake main boards without proper troubleshooting. Never bake power supply boards - they don't have BGA components.

[RainStorm]

Re: Toshiba 49l621u BL_ON to DIM jump repair

I only temporarily wired BL_ON to DIM, can LED backlights be that intermittent where if you force them on they will work properly afterwards?

TV's been doing fine now, just watched a movie on it.

[jjanssen7]

Re: Toshiba 49l621u BL_ON to DIM jump repair

Yes, especially that model. I have had the same experience as you in the past, only to discover that one of the LEDS was failing (and finally failed). I suspect you'll have that TV apart again...