LVDS - Page 1
Forum section: electronics / general

author: toni31
author_rank: Contributor
timestamp: September 06, 2013, 12:48:05 pm
content: This is my first post here and i hope for a solution.I have a laptop and i make some experiment on it and i have a question. The schematic shows that the lvds con have 3 pair of pins (txloutp0,1,2/txloutn0,1,2) when i put the DMM there i take 0V should i take anything there or not?Can i use DMM or should i use an oscilloscope (that i haven't).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 06, 2013, 12:52:04 pm
content: These signals can operate into the high hundreds of MHz to low GHz range, you'll need an expensive scope to see anything meaningful

author: amyk
author_rank: Super Contributor
timestamp: September 06, 2013, 02:09:03 pm
content: The voltages are also very low - hundreds of mV at most.

author: Stonent
author_rank: Super Contributor
timestamp: September 06, 2013, 04:10:16 pm
content: Low Voltage Differential Signalling. It is commonly just associated with displays but is also used in other things like server hard drives.

author: toni31
author_rank: Contributor
timestamp: September 06, 2013, 04:10:58 pm
content: any suggestion what to do?

author: c4757p
author_rank: Super Contributor
timestamp: September 06, 2013, 04:31:00 pm
content: What do you mean? Is something wrong with it?

author: toni31
author_rank: Contributor
timestamp: September 06, 2013, 06:34:46 pm
content: I just want to know how to troubleshooting black screen of laptop.

author: cyr
author_rank: Frequent Contributor
timestamp: September 06, 2013, 06:48:26 pm
content: Start by checking the backlight.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 06, 2013, 06:49:23 pm
content: Quote from: toni31 on September 06, 2013, 06:34:46 pmIsn't it just the backlight that is broken? Get a flashlight, point it on the screen and find out if you can see anything.

author: Stonent
author_rank: Super Contributor
timestamp: September 06, 2013, 07:56:49 pm
content: To troubleshoot a blank screen you first need to make sure the laptop is working by connecting a monitor to it before turning it on and then seeing if it works.Second check that cables are not loose. It is not uncommon for the cable to come loose from the back of the screen or inside.Check the backlight by shining a flash light into the screen at various angles. (as stated above)If your laptop uses a CCFL tube there will be an inverter board below (usually) with a pink and white wire coming from it (usually) that will have a voltage in the thousands usually.If the laptop has a CCFL tube, it is not uncommon for the tube to crack if the screen gets hit.Sometimes the magnetic reed switch in the screen or laptop fails and causes it to think the lid is always closed, that can cause the screen to not come on.247laptopLCD.com in the US has really good prices on screen parts.

author: toni31
author_rank: Contributor
timestamp: September 07, 2013, 06:01:30 pm
content: Thanks for all the answers guys but...let's say i do everything you say and the problem its not on the screen or backlight how to check if i have all signals at the M/B connector to make the lcd functional.

author: edavid
author_rank: Super Contributor
timestamp: September 07, 2013, 06:35:50 pm
content: Quote from: toni31 on September 07, 2013, 06:01:30 pmThe only sure way is to plug in a replacement screen

author: tom66
author_rank: Super Contributor
timestamp: September 07, 2013, 07:27:48 pm
content: You -CAN- use a 50MHz scope to see if there are some LVDS signals present, but don't expect to see much detail.

author: toni31
author_rank: Contributor
timestamp: September 07, 2013, 08:22:54 pm
content: I don't want to see details about the signal just to confirm if exist any signal there to exclude or not graphic failure so you believe that i can do this with a Rigol DS1052E (if i borrow one)

author: rexxar
author_rank: Frequent Contributor
timestamp: September 08, 2013, 04:33:31 am
content: Quote from: toni31 on September 07, 2013, 08:22:54 pmThat's why you plug in an external monitor. It's not very likely that one output of the gfx card dies and the other is still good. If you want to hunt for signals, go for it, but most likely if an external monitor works, you just have a dead panel.