Benq FP71G+ Q7T4

[JasonC]

I have a Benq FP71G+ model Q7T4 which I am having some problems repairing.

The original symptoms are when the monitor is switched on the Benq splash screen appears and then the LCD displays the computer signal for around 2 seconds before going blank. The power light remains green. If I power cycle the monitor then the same symptoms repeat.

I have checked out a bunch of threads on this forums about similar issues but in most cases even though the LCD monitor & model were the same the PSU board is of a different design.

I have limited electonic diagnostic skills at a board level but I can do repairs when directed what the fix is. In this instance I just decided to replace the whole PSU board since I thought the inverter circuit had developed an issue and I didn't have time to check/repair it in further detail. I did this and the monitor ran fine for around 3-4 days (8-12hrs a day) and then failed with exactly the same symptoms as the original issue. I got the supplier to send another PSU board, but it would only run for 20mins when cold. As it got hotter it would run for less time till it was down to about 10sec.

I tried to find a repair guide with a circuit diagram of this PSU board but all the ones I could find contain the other design like the ones mainly shown on the other threads.

I have attached a front and back photo of the PSU board for reference. The part number of the PSU baord is 4H.L2E02.A35.

The supplier of the replacement PSU boards gave instructions for disabling the protection circuit on the PSU which I did not think was such a great idea. I guess this activates when the CCFL is faulty and I am wondeing if that is what is happening in this situation since two replacement PSU boards both have failed.

[sabre504]

Re: Benq FP71G+ Q7T4

Hi it would be unusual for 3 psu to have the same issue

Sounds more like a bad solder joint on one or more of your ccfl's or an issue with the video board (post a pic others will ask )
Do you have access to another lcd screen or some ccfl lamps to test with.

Also where abouts are you so people can direct for buying spares and so forth

[JasonC]

Re: Benq FP71G+ Q7T4

I agree it is unlikely for 3 PSU to be faulty. (I guess the only chance of this is if the original IS faulty and both of the replacements are NOT new like the seller said they were but he says he has had no problems with other sales. Also another PSU purchased from this supplier for a different model monitor fixed the problem instantly and its still going strong 2 weeks later.

I have attached photos of the logic board but I would have thought it strange for this to be an issue if the 1st replacement PSU ran the monitor for around 40hrs before failing. I find it hard to suspect any other component of the monitor is faulty because of this fact. I guess I am making assumptions here and if there is one thing I have learnt about technology that is not to assume anything.

I have another LCD screen but its not from the same model monitor so I figured the ccfl lamps won't be compatible.

I am located in Australia.

[sabre504]

Re: Benq FP71G+ Q7T4

what model monitor is it from ?
A lot of them are compatible but for test purposes you only need to plug in the ccfl's assuming they use the same plugs

[JasonC]

Re: Benq FP71G+ Q7T4

I checked out this thread (https://www.badcaps.net/forum/showthread.php?t=7565) and then decided it would be a good idea to get a look at the ccfl tubes in my panel.

See attached photos.

I have noticed that they have a small amount of blackening at the opposite end to the leads which I am guessing is not good.

So can one faulty tube cause the whole inverter for all 4 tubes to shutdown? - because that would explain my issue - and hence the PSU suppliers protection override might be a sensible troubleshooting technique. Doesn't explain why the latest replacement will run the tubes for 20mins when its cold however whereas the other two PSU will only run for 2sec or so.

Question from here is there any technical way to test the tubes to determine if they are faulty without any specialised equipment for this purpose?

[sabre504]

Re: Benq FP71G+ Q7T4

Your tubes are on their way out and yes this would cause your problem ,
as you have them out you can plug them into the psu and fire it up but be careful and watch them they wil probably flicker or show a slight pinkish hue

You say you have another panel what model monitor was it from

[Scenic]

Re: Benq FP71G+ Q7T4

if they have a slight pink-ish tint when lit up cold, they're on their way out.
the more pink-ish it is, the worse is the condition..

worst i've seen so far was a pair of CCFLs that lit up bright red.
came from an industrial monitor.. no shutdown feature on the inverter.. it just runs them into the ground no matter what..

edit: 2nd pic, lower pair: actually looks like the CCFLs are cracked?!

[sabre504]

Re: Benq FP71G+ Q7T4

Just had a closer blown up look and still not sure if they are cracked but would def say they need replacing

[JasonC]

Re: Benq FP71G+ Q7T4

The other panel that I have is a LM170E01(A5). There is also another barcode with number 6091L-0163C and 040320NGSP on it and a ccfl warning.

The ccfl high voltage leads are the same on both this panel and the BenQ monitor panel.

The panel comes from a kiosk PC which had a bad mainboard. The mainboard was not repairable easily and no spares were available (it was only a celeron anyway) The panel was driven by a custom mini-PCI board (might be AGP actually). The panel itself is fine but I don't have any logic to drive it. It has a custom inverter with part number FIF1742-32C and FB040116 on it.

[sabre504]

Re: Benq FP71G+ Q7T4

Post a pic so we can see it

[JasonC]

Re: Benq FP71G+ Q7T4

Here are the pics of the spare display panel I have. If these ccfl tubes are compatible then it might be an easy way to test.

Also if anyone can identify the controller PCB or know of any way I can drive this panel feel free to chip in. I do have the mainboard it plugs into but there is nothing relevant on it really. The socket it plugs into is labeled AGP1. The mainboard is a LPC-845G. (Not looking to fix it as the main body of the kiosk has been ditched)

[sabre504]

Re: Benq FP71G+ Q7T4

Well i would suggest you hook this panel up using the guts of your benq .
It looks like there are side rails on the screen if they come off would it fit inside the case of the benq if it does give it a try looks like it would run video as well but if not will run as a tester to see if it shuts down.

If the video board wont connect it wont matter as long as you have a vga connection from a comp to it it wont go into no signal shutdown and see if it runs .
But i am pretty certain its the lamps that are at fault on your other screen .

[bomcla]

Re: Benq FP71G+ Q7T4

change the two transistor side down on power board !

[JasonC]

Re: Benq FP71G+ Q7T4

Just had a closer blown up look and still not sure if they are cracked but would def say they need replacing

I know how I hate finding a forum thread with a reported problem but no followup result so:

I would just like to report that it was indeed the tubes which were crook. I was able to obtain some replacement tubes from eBay which fixed the problem.

I would however say that if you are considering doing this get the tubes with the cables attached as soldering very thin CCFL and associated wires is a hassle and its very easy to snap them.

You do however need to be careful as the rubber endcaps do differ slightly between display panel parts and this may be a reason to get the bare tubes so you can re-use end caps.

[marky78]

Re: Benq FP71G+ Q7T4

Hello, i have a LCD Monitor BENQ FP92W Q9W5 and my screen got brooke, i find another screen but i forget how can i connect the high voltaje lamps 4connectors to the electronical Benq 4H.L2E02.A35. There are 4 connectors CN801, CN802, CN803, CN804 and i do not remember where to put cable with pink/white and lightblue/black. Tanks

[budm]

Re: Benq FP71G+ Q7T4

Pictures of the board? There is are two lamps for the top edge of the screen, and two lamps for the bottom edge of the screen, each lamp has two wires so you just treat each lamp as individual. The two lamps for the top can go into any one of the two lamp sockets close to the top edge of the screen, same for the two sockets for the bottom edge of the screen.