TFT backlight fluorescent lamps turns off after power on - Page 1
Forum section: electronics / repair

author: highcap
author_rank: Contributor
timestamp: January 24, 2025, 02:44:02 pm
content: So I got this IBM rack monitor with a 17" TFT, and this is how the CCFL's are behaving.Any ideas if this is a cause of the inverter or the lamps?Video in Youtube URL as I couldn't attach video:https://youtube.com/shorts/UgfCDV4TlocThank you for any input!EDIT:If I put a flashlight on the screen I can see the moving message "not connected, dsub analog".I guess some standby mode on the lamps can't happen that soon in jut 2 seconds after powering up the monitor (I have yet to add a VGA connector and feed signal, as the signal wire is cut)

author: tooki
author_rank: Super Contributor
timestamp: January 24, 2025, 03:47:50 pm
content: You just show them going on and off.A proper description of a fault explains what is happeningand how that differs from the expected behavior, which you also should explain.Since we can only guess, perhaps the inverter — the lamps look fine in the video. If they turned pink or green, or were uneven or very weak, then you know the lamps are failing.Why not connect a VGA signal so you can rule out that it is, indeed, going into standby?

author: Hr_Satch
author_rank: Contributor
timestamp: January 24, 2025, 06:13:28 pm
content: Often, the Backlights start pulling too much current,and the controller turns them off for safety reasons ;-?I think your Backlights are failing, . . .Or first check the Backlights power supply voltage, maybe she's dropping too muchunder Load, hence => Caps to change.Watchout it can tickle in your fingers when touching lines

author: MathWizard
author_rank: Super Contributor
timestamp: January 24, 2025, 11:49:39 pm
content: Another common thing on older LCD's is when certain output caps start failing, and the controller IC turns off the backlight, but yeah the image is still there like you did w/ the flashlight. In Britain they call those 'torches' and it still catches me off guard sometimes.If you know some safety precautions, I'd open it up and see what the output controller is doing. It's probably shut itself down.

author: highcap
author_rank: Contributor
timestamp: January 27, 2025, 12:31:32 pm
content: I see, so the lamps might be good if they're not pink/green, uneven or weak.The lamps fail to remain lit immediately after power on, but putting a flashlight on the screen the standby/not connected message roams within, thus deducing the fail (turns off after power on, in the title).I might have a inverter issue then.The VGA cable is cut unfortunately, so I need to first make the connections back.Thank you for the reply.EDIT: Turns out the little reply button next to each post is misleading and need to quote someone to reply directly. The above was meant for tooki specifically.From the opinions of all the posters, I'm doing to troubleshoot the inverter next / change the 471 3Kw caps.Thank you all for chiming in! I will get back with updates on the repair.

author: wraper
author_rank: Unknown
timestamp: January 27, 2025, 01:09:15 pm
content: Quote from: highcap on January 24, 2025, 02:44:02 pmCan be either. Usually it's bad electrolytic capacitors in inverter/PSU, bad secondary transformer winding (either open circuit or DC resistance is way off compared to another winding) or bad CCFL. If it's either of the latter, one of the CCFL often does not light up actually, and protection circuit disables the inverter after a moment.