LCD Monitor troubleshooting - Page 1
Forum section: electronics / repair

author: TorArne
author_rank: Contributor
timestamp: October 31, 2014, 11:27:58 pm
content: Hi,I'm new here, so this is my first post.I have a HP LA2205wg 22" screen which has gone black.I have tested that the CCFL tube is working, and it seems to be working ok.I can see a really faint picture, as if the CCFL tube isnt working.. but it is. (atleast it lights up when i power the monitor on)I have measured most of the caps, and none are bad.Anyone got ideas on what to measure/check next?I actually got 3 or 4 of these monitors, all with the same error..So if i fix one, i fix allTor Arne

author: wraper
author_rank: Unknown
timestamp: October 31, 2014, 11:43:49 pm
content: It lights up and works or switches off after a second or two? Is there only one CCFL tube or two of them? Post a picture of the PSU PCB.

author: TorArne
author_rank: Contributor
timestamp: November 01, 2014, 12:08:04 am
content: The screen it self doesnt seem to light up at all.The CCFL turns on.Its just a stable very very dim picture.Edit: I will actually do a recheck that the CCFL actually does light up

author: SeanB
author_rank: Super Contributor
timestamp: November 01, 2014, 05:31:30 am
content: Check the fuse in the 5V rail ( F851 next to the red 5V wiring) but your most likely problem is a dead main board.I had one with the same power supply board, and that is what died. As I got it in a roadside pickup it was no loss to scrap it and only keep the CCFL tubes and driver.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: November 01, 2014, 07:26:20 am
content: You say youve tested most of the capacitors. Did you test the main cap , its been changed at some point, by you or someone else .

author: TorArne
author_rank: Contributor
timestamp: November 01, 2014, 07:42:41 am
content: Quote from: fluxcapacitor on November 01, 2014, 07:26:20 amI replaced the main cap, as i had it off and had a spare. (old one was'nt bad, but changed anyway)Quote from: SeanB on November 01, 2014, 05:31:30 amChecked the fuse, works like a charm.You didnt manage to fix the dead main board?Tor Arne

author: SeanB
author_rank: Super Contributor
timestamp: November 01, 2014, 06:00:14 pm
content: Plain VGA input. Tiny board with a single chip on it with a hole in the top. Was worth more as scrap metal.

author: wraper
author_rank: Unknown
timestamp: November 01, 2014, 07:04:26 pm
content: So what with the lamps? Saying dim image, I understand that monitor is showing the image from the computer, just barely visible? If that is the case, main board cannot be dead. It can be only non working backlight or dead LCD panel. Second variant is very unlikely to be present on 4 monitors being exactly the same. On all monitors there is protection which shuts down backlight after a moment is something is not ok. Most common are: 1. one of the two (or more in the large panels) CCLF lamps is bad or 2. one of the secondary windings of the transformer(s) is faulty.

author: TorArne
author_rank: Contributor
timestamp: November 02, 2014, 11:27:49 am
content: I took some pictures.1 from a working screen (a samsung)1 from the broken screen (hp)There is also some flickering on the screen. unsure why.

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 11:41:47 am
content: Strange. Backlight is definitely working, at least partially. What happens if you change brightness in the settings from min to max, did you reset settings to factory default? Might be that backlight inverter works somehow, but below lowest PWM duty cycle limit.

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 11:53:07 am
content: Do you have oscilloscope?

author: TorArne
author_rank: Contributor
timestamp: November 02, 2014, 11:53:16 am
content: I opened the monitor so you can see the CCFL.And its on.. not extremly bright.. but its on. see picture.I have tried to change brightness and all.. also tried factory setting.. no go.

author: TorArne
author_rank: Contributor
timestamp: November 02, 2014, 11:54:05 am
content: Quote from: wraper on November 02, 2014, 11:53:07 amI do have a cheapass usb one.. not very good.. but should work for simple stuff.Can the CCFL tube partly be broken? or is it working.. or none working?Edit: I can get my hands on a working monitor.. same model.. and just switch parts around to figure out whats broken.. If that helps.Cant do that untill Monday thou (monitor at work)

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 12:04:44 pm
content: If CCLF would be dead, inverter protection should shut down. As you have oscilloscope, would be worth to hook it to transformer primary winding (between GND and terminal where transistor switches are connected) and post waveform here with min and max brightness setting. Just be very careful as there is something like 600-700V on secondary winding.

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 12:23:32 pm
content: BTW just noticed that you changed some capacitors. If you fix this monitor, throw those green Chengx junk away and solder original ones (suppose they were Rubycon) if you still have them, or get something better. Those Chengx are not only poorest quality capacitors but also have huge ESR. I once bought few, didn't check the brand they gave me at the local shop because they usually had Jamicon WL in stock which are green too. So when I measured, they had ESR like 2-3X bigger than general purpose capacitors with the same capacitance and voltage specifications. Moreover, they even don't write series on them, just LOW ESR which they obviously are not. There seems to be series marked on yours, but they are too tiny to be good compared to original ones anyway.

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 12:39:11 pm
content: As schematic don't seem to be available, write here IC model which is soldered on the small PCB near the transformer. I'll check datasheet and see where to measure PWM control signal. Photos of the Small PCB and back side of the big one would be useful too.

author: TorArne
author_rank: Contributor
timestamp: November 02, 2014, 04:14:35 pm
content: Quote from: wraper on November 02, 2014, 12:04:44 pmThat didnt go too well.Blew a fuse, and pc is dead.

author: TorArne
author_rank: Contributor
timestamp: November 02, 2014, 04:16:34 pm
content: Quote from: wraper on November 02, 2014, 12:23:32 pmI will change the capacitor back.Wasnt actually Rubycon on the big one, was a Elite brand.Is that any good?

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 04:27:10 pm
content: For high voltage capacitor elite is completely ok, order of magnitude better than Chengx anyway. On capacitorlab.com elite is mentioned as crap like all brands except japanese capacitors and samxon, but that list is about LOW esr capacitor failures what is not the case. IMO they are generally ok, especially if used where is no high ripple current.

author: Rick
author_rank: Frequent Contributor
timestamp: November 02, 2014, 04:30:34 pm
content: If it were me I would find a couple of ccfls and blindly replace the ccfls one by one till I find the defective one before doing anything else. I think the flickering may be due to one of them. Now we have cheap led strips sold with the driver here, but I think the ones sold on ebay are not that cheap.

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 04:42:37 pm
content: Quote from: Rick on November 02, 2014, 04:30:34 pmAs if it would be an easy job to tear apart LCD panel and you need to buy a new CCFL in the first place. With a huge risk to completely destroy LCD. BUT, as I said, if CCFL failed, inverted will shut down, end of the story. What I see here, for some reason inverter is not regulating PWM duty cycle. It may be inverter failure or no PWM control signal coming from the main board. I tend to think this is the first variant.

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 04:50:32 pm
content: Quote from: Rick on November 02, 2014, 04:30:34 pmI wonder about all those people who modify their monitors with the LED strips. Are they idiots or clueless? Even if it kinda works ok, color reproduction of the monitor will be completely fucked up. It will be impossible to get any acceptable color accuracy even if using calibrator.

author: Rick
author_rank: Frequent Contributor
timestamp: November 02, 2014, 05:39:24 pm
content: Quote from: wraper on November 02, 2014, 04:42:37 pmYou don't need to tear apart you lcd panel. There is a way to pull the ccfls out without destroying the unit, you open the metal frame at the four corners of it with pliers, and pull the ccfls out, it's easy. But it may be different for each monitor.

author: TorArne
author_rank: Contributor
timestamp: November 02, 2014, 08:02:59 pm
content: Quote from: wraper on November 02, 2014, 12:39:11 pmHere you go.Oscilloscope dont work anymore thou..Its dead, docs says max 600v.

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 08:19:59 pm
content: Quote from: TorArne on November 02, 2014, 08:02:59 pmDid you probe secondary of the CCFL transformer? Well, I warned. Or considering blown fuse, did you probe something connected to the mains? Well, I asked for primary winding, guess you probed wrong primary as I meant inverter?I asked for different board photo. Small PCB that sticks out of the PSU PCB near CCFL inverter transformer.

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 08:28:05 pm
content: Well, I think a bit late but worth watching.

author: TorArne
author_rank: Contributor
timestamp: November 02, 2014, 08:40:36 pm
content: Quote from: wraper on November 02, 2014, 08:19:59 pmI probably did something wrong yeahIts no problem, was a really cheap scope. (think it was 45usd)Tried fixing it.. but there's something really wrong with it.. so going in the trash.. hehe..Here's the correct board, probably.

author: bithead9
author_rank: Contributor
timestamp: November 02, 2014, 08:49:25 pm
content: FYI Great resourse for LCD monitor repair:http://www.badcaps.net/forum/Good luck on your repair!

author: wraper
author_rank: Unknown
timestamp: November 02, 2014, 10:45:24 pm
content: Here is schematic of this PCB. You should check highlighted signals. Measure voltage on C6 and C2. Post brightness min/max, switched off voltages. Don't know which particular brightness control input is used in this case. PWM is ON/OFF input + brightness (optional). Brightness can be controlled by PWM or PID which is analog brightness control input. If PWM is used, PID should always stay at +5V, otherwise voltage must change on it depending on brightness.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 02, 2014, 11:52:14 pm
content: Quote from: wraper on November 02, 2014, 08:19:59 pmYikes, don't probe the secondary with a regular scope probe! The voltage ratings are just for DC. Even with a 1000X probe I got into trouble, there's some serious power there at a high enough frequency to derate the probe to a much lower voltage!

author: Shock
author_rank: Super Contributor
timestamp: November 03, 2014, 04:44:49 pm
content: Here is a better picture of the boards. Having nice clear photos helps.I take it that you have done the basic stuff like try different inputs to the monitor, test it on a bios screen and reset the defaults to confirm they are indeed suffering the exact same problem?Since you have multiple of the same model can't you swap testing the CCFL cable connected from another screen? Will not work if they are in series though.I'd be checking the ballast caps and the HV transformer as well.Do you have a working one?

author: TorArne
author_rank: Contributor
timestamp: November 08, 2014, 10:10:43 pm
content: DIM 3,26vPID 1,29vNeed to connect a monitor to be able to adjust brightness. will try and do that nowTor Arne

author: TorArne
author_rank: Contributor
timestamp: November 08, 2014, 10:13:30 pm
content: Quote from: Shock on November 03, 2014, 04:44:49 pmI do have a working one at work.The rest i have are all broken with the same fault.I have tested reset to default and all kind of stuff.Nothing helps.Even the menu (without anything connected) is dim.I have testet ALOT of caps, not found a single bad one yet.Tor Arne

author: TheBay
author_rank: Unknown
timestamp: November 08, 2014, 10:22:49 pm
content: What panel is in this, Make and Model?, could be driver chips on panel or mainboard is weak, I don't think its inverter/ccfl issue.What voltages are present on mainboard from PSU?

author: TorArne
author_rank: Contributor
timestamp: November 08, 2014, 10:26:26 pm
content: Quote from: TheBay on November 08, 2014, 10:22:49 pmHere's a picture of it

author: TheBay
author_rank: Unknown
timestamp: November 08, 2014, 10:29:03 pm
content: Quote from: TorArne on November 08, 2014, 10:26:26 pmI had a feeling it would be an LG Display Panel for some reason!, the boards look like LG too but no markings, awful PSU/Inverter design. Did they really cheap out on parts lol.Can you describe the flickering, is it on the screen? or if you look behind at backlight is it that flickering?, is backlight bright when looking at the side of it? I have a feeling its Panel or scaler board.Do you have a hot air station and/or ESR meter?

author: TorArne
author_rank: Contributor
timestamp: November 08, 2014, 10:46:23 pm
content: QuoteI dont recall seeing the flickering on other monitors i got.Backlight dont seem to be flickering.

author: TheBay
author_rank: Unknown
timestamp: November 08, 2014, 10:48:06 pm
content: Have you got a hot air station and an ESR meter?The main IC on mainboard on these type of scalers sometimes get poor joints, caps are also weak.Check all voltages going in to mainboard too.

author: TorArne
author_rank: Contributor
timestamp: November 09, 2014, 12:06:31 am
content: Quote from: TheBay on November 08, 2014, 10:48:06 pmSorry, i do not have any of that.I do have a hot air gun thou.Tor Arne

author: TheBay
author_rank: Unknown
timestamp: November 09, 2014, 12:11:19 am
content: Do you have the right nozzles? Might be worth heating up the legs on the main scaler ic, also check pcb smd fuses etc.

author: wraper
author_rank: Unknown
timestamp: November 09, 2014, 08:56:27 am
content: Quote from: TorArne on November 08, 2014, 10:10:43 pmThen PID voltage must increase with increasing brightness. If it does not, try to solder a ~1k resistor in parallel to R13 and see if brightness becomes normal.

author: Vito_R
author_rank: Regular Contributor
timestamp: November 09, 2014, 10:06:50 pm
content: Quote from: wraper on November 02, 2014, 12:23:32 pmAgree get rid of those crappy Chengx caps. Replace all electrolytics with high quality low ESR Japanese caps and you'll extend the life of your board for many years. I like using Nichicon PW, HE, or HW series.

author: wraper
author_rank: Unknown
timestamp: November 10, 2014, 02:44:33 pm
content: Why should he replace all capacitors if they are all Japanese except one? It unliekely to provide much longer life as CCFL or backlight transformer should die first IMO. Even if some capacitor dies, it will be only one, not bunch of them altogether.

author: Vito_R
author_rank: Regular Contributor
timestamp: November 10, 2014, 05:50:45 pm
content: Quote from: wraper on November 10, 2014, 02:44:33 pmI meant only the chinese caps, not the ones he has already replaced with Japanese. Those chinese caps eventually will fail one at a time if you just replace the defective ones. Better to recap all at the same time then have to open up the monitor again when the next failure occurs.

author: wraper
author_rank: Unknown
timestamp: November 10, 2014, 05:53:17 pm
content: Well he have wrote previously that he will put original Rubycons back. Chengx were those he replaced. Actually I haven't ever seen that crap to be present in any monitor from factory.

author: Vito_R
author_rank: Regular Contributor
timestamp: November 10, 2014, 05:54:35 pm
content: Quote from: wraper on November 10, 2014, 05:53:17 pmI guess I missed that, sorry.

author: kimi007
author_rank: Newbie
timestamp: June 26, 2015, 04:28:28 pm
content: Hello J have the same problem.Rotate cables to lamps, but you must to extend it.That will solve problem.Sorry for my bad english.Best regards.Miki

author: luke9511
author_rank: Contributor
timestamp: October 17, 2015, 03:49:57 am
content: hello and good day all, i came across this thread while searching for a way to fix the same model of monitor as the op, i have about 4-6 of them all with the same issue there is a very faint picture, it is either very very dark or very dim and some flickering, does anyone have any ideas i can try?