lenovo a451 no backlight or hdmi output

[Thedan55]

hey all

ive worked on this model before and posted about that one here and found the solution. this is the same model but different machine.

ive checked the fuses f6 f7 and they are fine, and im getting 3v on power on from lcd connector pin 33 or i think 34 35, one of them is backlight power, cant remember of the top of my head.

so im leaning towards this being an actual lcd issue and not a board issue...

just wanted to get some second opinions before ordering a display for this. is there a way to test the actual display? when shining a light i can see the lenovo logo so the backlight is definitely an issue.

the thing that's confusing me is there's no display over hdmi either. in the past windows wouldn't boot because i needed to confirm something in the bios or something cant remember but once i repaired the fuse it all worked great.

cheers!!

[Vesko356]

Re: lenovo a451 no backlight or hdmi output

JEDP1: Pin 33 & 34 - 3.3V, pin 37,38,39 & 40 - 20V, pin 19,20,21 & 22 - 3.3V
Check these first. If all is OK, check the display pcb fuses.

[Thedan55]

Re: lenovo a451 no backlight or hdmi output

JEDP1: Pin 33 & 34 - 3.3V, pin 37,38,39 & 40 - 20V, pin 19,20,21 & 22 - 3.3V
Check these first. If all is OK, check the display pcb fuses.

will do, are these voltages in standby or while powering on? f6 and f7 are display fuses if im not mistaken and they're fine

[Thedan55]

Re: lenovo a451 no backlight or hdmi output

JEDP1: Pin 33 & 34 - 3.3V, pin 37,38,39 & 40 - 20V, pin 19,20,21 & 22 - 3.3V
Check these first. If all is OK, check the display pcb fuses.

right i know i checked 33 and 34 before and had 3v. backlight cntrl only has 1.2v but backlight on has 3v.

does that mean a controller is damaged?

edit: 20v on the 37 to 40. 3.3v on 19 to 22

[Vesko356]

Re: lenovo a451 no backlight or hdmi output

Check again the PANEL_BKLT_CTRL line voltage at test point TP57, if it's low again, check the resistance to ground at that line with and without connected display, inspect edp and JEDP1 connectors for corroded or bent pins, and finally check voltages at the CBT3257ABQ (U7).

[Thedan55]

Re: lenovo a451 no backlight or hdmi output

resistance to g OL with and without display at tp57.

u7
pin11 0v. 9 and 10 1.2v
pin16 5v
pin 5 0v, 6 and 7 3.3v

[Vesko356]

Re: lenovo a451 no backlight or hdmi output

Inject 3V at test test point tp57, backlight must turn on, just to check if the machine (and the display) is working at all, or not.

[Thedan55]

Re: lenovo a451 no backlight or hdmi output

Injected voltage not backlight

[Vesko356]

Re: lenovo a451 no backlight or hdmi output

...are these voltages in standby or while powering on?

While powering on, after the power on button has been pressed of course.

Injected voltage not backlight

If the cable is OK should work, In that case as I said check the fuses at the pcb board of the display, the cable itself, or test with any other screen.

.

[Thedan55]

Re: lenovo a451 no backlight or hdmi output

While powering on, after the power on button has been pressed of course.


If the cable is OK should work, In that case as I said check the fuses at the pcb board of the display, the cable itself, or test with any other screen.

.

Fuses are good, cable and connectors look good. I have image but no backlight even after injecting. Unfortunately i don't have another display. Seems like the display is bad?

[Thedan55]

Re: lenovo a451 no backlight or hdmi output

It's sorted ��������

Previous tech that replaced screen didn't secure it correctly and the flex on the LCD had come loose ��������������

After all that!

Thank you for your help! Genuinely appreciated mate @vesko356

[Vesko356]

Re: lenovo a451 no backlight or hdmi output

You're welcome. Well done!
Cheers