Laptop screen not turning on after motherboard and screen replacement

Dubem_

Estimable
Feb 7, 2016
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4,510
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I replaced my Dell Inspiron 7548's motherboard after the old one shorted out and refused to turn on. I also had to replace the LCD and LCD cable due to some cracks in the screen and pins falling out of the old cable. I installed the motherboard and when I turned it on, the display remained dark. I tested the screen by holding D while powering on and it worked fine and the backlight turned on too. I hooked up the laptop to an external monitor and the it kept saying 'No Signal'. The laptop fans work fine and change intensity but there are no beeps from the laptop to recognize what's wrong. I reset the CMOS battery, tried the 'hard reset' thing multiple times, and tried all different configurations of my RAM. The only time it beeps is when I remove the RAM completely (2 beeps). I removed the LCD cable and it still wouldn't beep. Please help, I don't know where to start fixing it as I don't even know what's wrong.
 

fagetti

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Mar 1, 2018
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remove lcd cable from motherboard and put external monitor cable, you get anything on external this method? might need keys to change input search your model form google. Beeps 2 is normal when ram is missing so it detects it. Dell inspiron not always give error beeps or flashes during "lcd error". If you remove LCD cable and boot to extternal monitor and get picture then its either cable / connector on motherboard or LCD itself
 

fagetti

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Mar 1, 2018
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Ok did your old mobo support ddr3l i look disassembly video looks like this model needs that? TRY this, remove wifi card, speaker connector, any external connector on motherboard and try to boot it first with new lcd connected and then with that disconnected and external monitor connected.

So remove everything but ram, cpu, dc jack ,heatsink and fans. (also try first this motherboard extension which i see in video first connected and then disconnected) You need power button still, some laptops can boot without when cmos battery is removed though. FIrst try with only these, then remove power button cable and cmos battery and when you plug in powr cable it should automatically start without pressing power button.
 

Dubem_

Estimable
Feb 7, 2016
7
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4,510
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I removed the LCD cable from the mb and booted to the external monitor, but nothing showed up. The monitor recognized that a cable was connected but there was "no signal" from the laptop
 

Dubem_

Estimable
Feb 7, 2016
7
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I removed all things you said to, but there is still no signal on the monitor and no video on the display. What do you mean by the motherboard extension?
 

fagetti

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Mar 1, 2018
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i just watched some disassembly video of your laptop and looked like some kind of extension board.
Try to remove motherboard completely, put it on cardboard box or wood table, without any dirt or something which could short it. Can you reseat cpu on this model? Do it and remember to lock it, remove dc jack and add it to mobo after removing it from case. Add external monitor cable to hdmi / vga whatever port you have. Check what dell has for changing input of screen so you can try key combinations to change from lcd to vga / hdmi

JUST have 1 ram, cpu, fan , power button connected nothign else then plugin cable to dc jack and press power button, look carefully that you wont short motherboard or anything else while doing this. Reaseat heatsink and dont screw it too tight! look for anything shorting, example heatsink touching cpu or gpu components near core (where you add thermal paste)

Is your ram sticks pc3L or pc3? You need to use right ram for motherboard check sticker what it supports,, it should say Supports only DDR3L if that is. Maybe your old mobo supported ddr3l and this wont etc check this

You can also test without fan but VERY fast remove charger immidiattely after you see if picture is coming or not, removing power button might work if you remove CMOS battery your laptop should start automatically when applying charger to dc jack. Im not sure about your model though.
 

fagetti

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EDIT: and dont remove heatsink or touch anything while power is plugged in ofcourse

And you can try reset cmos when you remove bios/cmos battery press power button for 1 minute without power plugged, this resets cmos.
 

Dubem_

Estimable
Feb 7, 2016
7
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4,510
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I removed the motherboard from the case, saw that there was no way to reseat the CPU, plugged it into the external monitor, turned it on, but there was still "no signal" on the monitor and no display on the LCD. I tried the buttons F8 + FN to try to switch the input, but still nothing showed up. The motherboard is the same model as my previous one which used ddr3 RAM and I'm using the exact same Ram so that shouldn't be it. I tried other DDR3 RAM but it made 2 beeps when I tried to use those. I cleaned off the processors and made sure there was no contact with anything that could short it, but still nothing showed up. I also reset the CMOS battery, but still nothing showed up.
 

fagetti

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Mar 1, 2018
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2 beeps is ram error so your motherboard recodnizes wrong ram thats ok. Can you take high resolution pictures of motherboard both sides, new one and old one. If you have multimeter check cmos battery voltage if its over 3voltage its okay but if not replace with cr2032 3.3v battery
 
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