Vizio
Ground score hacking...
Service manual https://www.manualslib.com/download/913811/Vizio-Vx42l-Hdtv10a.html (no mention of service port)
This from explorations of a Vizio VW42L HDTV10A found on teh sidewalk.
The unit came with a power cord, when plugged in the vizio logo lights up amber, and then turns white when the power button is pressed. The screen remains dark however the backlight turns on within a couple of seconds. Also the optical audio link starts to glow red indicating some life. Otherwise the device seems to be non-functional, loose link/chip between CPU and LCD?
There's a RJ-12 jack on the back that is labeled SERVICE. This appears to be a TTL Serial interface, with Pin 5 as Tx. Connecting Pin 5 and a ground with serial configured at 115,200 bps yields the following on power up.
SYSPLL now is 324000000 Hz DMPLL is set as 378.0 MHz The memory is DDR-I 2 Chips DQS 0 - (0 ~ 42) set 21[0x15 - 0x28](0xed) DRAM is set as 32 bits Set PSPLL to 148500000 Hz... Set VPLL to 81000000 Hz... Set ADCPLL to 81000000 Hz... Set B2RPLL to 148352000 Hz... Calibrate APLL1 to 270950400 Hz... Calibrate APLL2 to 294912000 Hz... MT5371 Boot Loader v0.2 Booting... Decompression image to 0x02b00000...OK! Image size: 5112656 bytes (0x02b00000 - 0x02fe034f) Starting image... Before IRRX State: 0 After IRRX State: 0 DRAM_CLK: 189000000 bApiTunerInitInUSA ch1 calibration start input offset calibration is 1 Transition point is 14 ch1 calibration is done input offset calibration is 1 Transition point is 15 DTV>