Getting inside an LCD panel

[Loa]

Hello,

Anyone here knows its way inside an LCD panel? Not the monitor, the panel itself. I have an old Apple Cinema Display with a backlight that won't stay on. Everything else about the monitor works perfectly: I can even see the screen working when I shine a light directly into it. It's just the backlight.

Loa

 

[DanielCoffey]

If the iFixit site doesn't have a teardown, there was a thread on this forum about backlight issues with an ACD which linked to a teardown. The fault they had in the thread was the seal between the panel and the backlight coming loose and creating a wavy shadow on the screen. I know your issue is different but it will be a starting point.

EDIT : found it... https://forums.macrumors.com/threads/1741524/

That should give you information about getting inside and seeing if the backlight connector is loose or not.

 

[Loa]

Hello,

Thanks for the link, which does lead to a "Deeper" teardown than iFixit's. I've disassembled the monitor many times now, but haven't tried the panel itself. I'll give it a try.

Loa

 

[laurihoefs]

Before you open the panel, make sure the power supply and inverter are ok. Take a look at the power supply capacitors: if they have any brown or white residue on/around them, or have bulging tops, they are the most likely cause.

If there's no clearly visible issue, you'll need a multimeter to check the PSU voltages, and maybe to test the inverter transformers and diodes for short circuits. Unfortunately quite often the easiest way to determine if an inverter is defective, is to replace it with a known good inverter and see if that makes a difference... Fortunately inverters are not that expensive.

The backlight should be fairly easy to replace, just handle the detached panel carefully. The ribbons (FPC cables) attached to the top edge of the panel are somewhat delicate, and some of the electronics that drive the panel are often actually on those ribbons. The ribbons are attached to the timing controlled board (TCON) usually mounted on the back of the panel assembly, to get them loose you need to carefully flip up the lock of the zero insertion force (ZIF) connectors (the lock is open in the linked picture).

Goog luck with the repair

 

[Loa]

Hello laurihoefs,

I've checked every "easy-to-check" thing in the display. Following Apple's technician guide for LED display I verified that the panel itself receives its 24V. It does. The logic board and power supply board seem to be alright. I've also tested the inverter cable, that apple calls the LCD function interface. Every one of the tiny wires works (continuity tested using multimeter).

The display even "displays", just without any backlight.

My problem is that I'm not sure how "openable" the panel itself is, once it's out of the monitor.

Thanks for the help.

Loa

 

[Loa]

Hello,

Small update. I've been able to go down all the way inside the panel and I've seen the backlight (not what I was expecting). Trouble is: everything seems fine. The cable that powers the backlight is fine, and I've tested all the individual mini wires: they all check OK.

I'm kind'a stumped now...

Loa

 

[laurihoefs]

My problem is that I'm not sure how "openable" the panel itself is, once it's out of the monitor.

The panel is usually sandwiched between a backplate and a frame. The frame is either screved to the backplate with a couple of small screws on the sides, or just has a couple of plastic clips that hold the whole thing together. Either way, once you get the frame out of the way, the panel, diffusers/reflectors and the backlight can be lifted out of the backplate.

IMHO the PSU or inverter are still the more likely culprits though, they might only start misbehaving while loaded, and show no failures when tested. But if you have already tested them thoroughly, then the backlight lamp might be going bad.

Edit: the lamps are quite delicate. If they are nested in white plastic holders, see if the the whole assembly (lamp + holder) can be detached from the backplate without separating the lamp from it. This way it's easier to keep the lamp in one piece.

Edit2: Oh, wait, you mentioned it's an LED display, so forget the parts about the CCFL assembly and inverter... But the same applies: if the PSU and DC-DC-converter both work, the next part to check is the LED strip inside the panel assembly.

 

[Loa]

Thanks for the tips.

I haven't found anything on the net that explains how I can test the led strip itself. Any ideas?

Loa

Edit: I'm currently writing this on my Cinema Display. I plugged it and unplugged it about 15 times and somehow it stuck. I'm not under the illusion that it's now fixed, but maybe someone who knows panel might see the fact that the problem is intermittent as a clue...