No screen display but back light works on laptop - Page 1
Forum section: electronics / general

author: G7PSK
author_rank: Super Contributor
timestamp: September 13, 2012, 01:37:48 pm
content: Hi I have an HP 530 laptop that has no display but the back light works. It works with an external monitor and I have tried another cable but still no display. Do you think that this is the screen or the motherboard at fault, there are a lot of electronics on the lcd panel itself so I wondered if this is where the fault may lay. I don't want to get another lcd if the mother board is dud. In control panel I get the message that this display is disabled. As it is a friends laptop not mine I don't want to mess with repairing the mother board as I will be held responsible for ever more whenever it develops another fault. The computer is running Vista.

author: westfw
author_rank: Super Contributor
timestamp: September 13, 2012, 02:54:29 pm
content: QuoteI bet that that means that the display is disabled! (in software, so that there is some magic key sequence or bios setting that will re-enable it. fn-f4 ? (yeah, it shouldn't drive external only if there is nothing connected, but ... software has bugs.))Second guess would be an unseated connector between video card and LCD. Worth taking apart and poking at before tossing in the towel...

author: G7PSK
author_rank: Super Contributor
timestamp: September 13, 2012, 03:14:11 pm
content: Checked all the connections, even replaced the cable thinking that it might have a break where it passes around the hinge. I suppose the bios might be corrupt, I will have a look at that It certainly does not toggle between external and on board or at least it does if I turn of the on board screen the back light goes out and the external on screen still displays the other way around the back light stays on and the external screen goes off or both screens can be on but only the external screen has a display, so it would appear that either the LCD and its electronics are dead or the mother board is bad. The video chip is working though.

author: Monkeh
author_rank: Super Contributor
timestamp: September 13, 2012, 03:48:19 pm
content: The only way to diagnose these things is to swap a part out and see what happens. So you'll need a replacement panel or motherboard.

author: G7PSK
author_rank: Super Contributor
timestamp: September 14, 2012, 07:32:36 am
content: I checked the video out put on the internal screen, with a scope, found 3 pins that were ground 3 at 3.31 volts and 6 that had various signals that looked like video and digital. Also found that when on the mains power supply there is 97 volts AC on the chassis regards to earth so I checked the output plug on the mains adapter and found the 97 volts AC on both the inner and the outer, with enough power to light a neon screwdriver yet if I measure terminal to terminal the AC volts is only about 0.03 volt.

author: Alana
author_rank: Frequent Contributor
timestamp: September 14, 2012, 08:46:18 am
content: Don't bother with AC voltage from mains earth to + and - pins of lappy PSU - this is normal in PC and laptop PSUs if they have their mains earth terminal unconnected.For LCD - every time i had such problem there was some signal missing.In one HP i was fixing it turned out that ground was poorly connected - in this part of ribbon cable that is closer to lappy mainboard they connected ground wires without any soldering and this had gone bad. Part I'm referring to is in this fabric based insulation tape.

author: amyk
author_rank: Super Contributor
timestamp: September 14, 2012, 10:00:09 am
content: Here is the connector pinout.The DISPLAYOFF# signal looks interesting.