Don't Miss

How To Repair LCD Monitor Flicker- HP2509m

By on July 12, 2016
repairing lcd monitor









lcd monitor

lcd monitor repair

Previous photos showed the Power Board of the 25 inch HP 2509m Monitor this repair is about.

On next photo also the TV Mainboard is shown on the right.

how to repair lcd monitor flicker

My friend Frans found a dirt cheap but bad working HP 25 inch Monitor with HDMi and VGA inputs. The complaint was that the screen was flickering continuously. The flickering never stopped after it was switched on.

At first I checked the internet and found a couple of Forums that told to check for the components on the Inverter Board. Supposedly the Inverter Board (the 17 Pins vertical placed Board located on the right from both HV Backlight Transformers on the left in above photo) had some Mosfets and/or a Diode that needed replacement.

But I checked the Inverter Board with a 16-pin INL816gn controller that had a P-Channel Nikos P9006edg (Q1) and a P5506bd N-Channel Mosfet (Q2) and could not find any error. Also the on the left of the P9006 placed Diode (D1) was fine. Nevertheless I noticed that I had none of these special 60V Mosfets, so I ordered a couple of both through Aliexpress. Because most 8 pins Laptop Mosfets SMD chips are only about 20V maximum and those will not fit here either.

I searched for the specs of the INL816gn Inverter controller but there seems to be none. Only a small description of the 16 pin functions can be found (see the end of this article). I did however find a Dell Service Manual of the LCD Monitor E190Sf that did use this same Inverter Chip as can be seen on Page 5 of this Manual. But after comparing both circuits with that of our Flickering 2509m Monitor I noticed that both Mosfet Gates were connected differently. INL816 Drv pins 1 and 16 (DRV1 and DRV2 gate signals) were directly connected to both gates in the Dell Monitor. Which was not the case in the HP 2509m 25 inch Monitor were only the P5506 Mosfet was attached directly with its Gate to the INL816 DRV output pin. The Gate of the P9006 was driven indirectly by a capacitor and also had the earlier mentioned Diode attached. Still both Mosfets could be checked functionally by just

using both Testleads of a Digital Multimeter in Diode/Beep test. Only Mosfet P9006 won’t show a very low switched through RDon resistance between Source and Drain because of the attached Diode D1 (a type PJ999 SR26). But the P5506 will! And to be 100% sure I also tested both Mosfets with my M12864 ESR/LCR Semiconductor Universal Tester after I had disconnected them from the Board Circuit each with my Gordak 952-A Hot Air Solder Station (one of 2 Hot Air Stations I have).

fix lcd monitor

Because the Inverter was not defect apparently (See example photo above) and none of the copper Layers were damaged either, I soldered it back into the Power Board.

I noticed on the internet that they also sell Inverter Replacement Sets for the HP 2509m Monitor but they are only to repair the Inverter itself and explicitly NOT to fix the Flickering problem of the HP 2509m ! (See: HP 2509M Monitor PS ILPI 162 Repair Kit No Power Won’T Turn On _ eBay_files). This also convinced me to look further for the real cause why this Monitor was flickering continuously.

Next I used my China made CFL Tester and my CFL Tubes from an old scrap LCD Monitor I saved for Test Purposes. See next photo below of the CFL Tester which I already had repaired after once blowing it up by using to much input Voltage. That’s why I wrote the Max Voltage Warning text on the Inverter Transformer. To prevent having to replace both transistors afterwards again (2 x UTC D1616AC).

Both CFL Tester transistors were easily obtainable and so I previously also bought a couple of them to have some spare parts just in case I would need them again. I attached my saved Test CFL lamps to all four Power Board Backlight HV connector outputs and they all worked without any problem whatsoever. So this indeed confirmed the fact that the Inverter on the Power Board was working fine ! (and I probably had better checked this first but I am always checking Components, Solder side and so on first to prevent blowing more parts up in the meanwhile during the testing process. And burned/blackened parts can’t be read anymore so…).

flickering in lcd monitor

bad backlight

Above photo shows the right side of the 2 CFL Test Lamps (Cold Filament Lamp) and the photo before that showed the CFL Lamp Left side were the Wires and both HV Connectors are attached. These CFL Tube Lamps are of course very fragile and also contain poisonous Mercury which comes free when broken. (Also the liquid in broken LCD screens is very Poisonous so be extra careful! And keep it away from Hands, Mouth, Eyes and so on.)

I finally checked the integrated 2509m Monitor CFL tubes themselves one by one by connecting them, by using my own CFL Test Lamps to close the unused Inverter HV Outputs to keep the Inverter from stop working. (the Inverter keeps track of the Output Load while activating the HV to the Transformers continuously).

And only the top 2 CFL Lamp (which consists of 2 tubes in one reflector unit placed in it parallel) seem to create a problem. So the 2 bottom CFL Lamp was fine. And further investigation revealed that the top CFL was making a crackling/Sputter noise in the left top side of the Monitor were the CFL Light was mounted. Which means much more work to disassemble the LCD or the CFL Lamps in it.

And because opening the HP Monitor was one thing, removing the CFL from the LCD was a completely different matter. Why I searched the Internet to find the HP Disposal Instruction Manual of this Monitor which also should explain how to extract these CFL Tubes safely. And I found this HP manual: disassembly_monito_201041519166. Also known as the Product End-of-Life Instructions Manual.

Next photo shows my collection of saved CFL Backlight Tubes as can be found after disassembling A4 Flat bed scanners, Fax machines, Monitors etc. Notice my green Bottle I re-used to function as CFL tubes holder.

how to repair flickering lcd monitor

Before everyone uses this Disposal Manual from HP I have to warn anyone NOT to do the Steps 12 and 13 in the PDF manual as it most likely will lead to broken CFL Lights. Because I tried those Steps and still couldn’t retrieve the CFL tubes for even a single millimeter this way. And I didn’t want to use too much force to prevent leaking out of the Mercury either. So I completely opened up the LCD on a large working table by removing ALL screws and every Frame until I was able to lift up the complete Back plane with the CFL on top of it. And I was able to lift up the back plate up out the construction.

Also carefully without making the LCD dirty on the inside to prevent any visually dust and stains showing up later. And this way I could easily detach the CFL Top tubes without breaking them. As it turned out the no wire side of the both tubes had a bad spot were (maybe turning into Carbon which is also a semiconductor) the isolation was damaged. And in the Monitor Cabinet I also had to remove some small broken off parts on that spot also. And while replacing these tubes isn’t easy, nor possible without a low price tag, especially if a company does it for you, I decided to insulate the CFL with Standard Insulation Tape myself.

I used the red Tape Roll to cover with a few small tape strips the damaged CFL tube side and about 2 to 3 layers thick so it still would fit into the frame.

fixing lcd monitor

In the previously mentioned way the CFL tubes can easily be picked off from the white Reflection Back plane Plate. And placed back on it without any force also easily. After reassembling the whole LCD and putting every Board and Connector back into place, (one should use the HP Disposal Manual also to see how everything can be disassembled and how the HP 2509m Monitor can be opened) I noticed the Flickering problem had gone.

HP apparently discards these types of Monitor problems as non repairable, which would require the buyer to look for another Monitor. To show what parts of the HP Disposal Manual should be avoided at all costs the following PDF pages show Steps 12 and 13 I did not use because the CFL tube wasn’t going to be extracted in one piece this way ! Notice that HP also uses LG Displays!

The last photo finally show the repaired and like new working 25 inch Monitor ! So don’t throw away your great Monitor thinking it can’t be fixed anymore. By-the-way: I also checked the temperature of both Mosfets (at a room temperature of about 24.5 Celsius) on the Inverter Board and the HV Transformers before closing the Monitor Case. Checked with my 9V operated IR 260-8S contact-less Thermometer both Mosfets were about 54 degrees Celsius. And both Transformers a bit cooler!

repairing flicker lcd monitor

troubleshooting lcd monitor

Until another Fix !


Albert van Bemmelen, Weert, The Netherlands

Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.

P.S- If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!

Note: You can read his previous repair article in the below link:




  1. Humberto

    July 12, 2016 at 9:55 pm

    Wow! Albert what a tedious job, patient is the key that's why you finally obtained the expected result. Congratulations.

    • Albert van Bemmelen

      July 12, 2016 at 10:44 pm

      Indeed and my friend was happy too! At first I wasn't sure if I would take such a risk in completely opening the LCD frame. But I was very careful and only opened the frame only enough so I just could extract the bad top CFL lamp out, and clean the inside before closing the frame as quickly as possible (to prevent dust or anything else from entering the inside of the screen by for instance Static electricity) while holding the big Glass Plate that was facing downwards.
      It was that or throwing it away. And since the HP 2509m Monitor had only been in use for about 5400 working hours according to its internal counter, it still has left some 60.000 minus 5400 more hopefully.

  2. Parasuraman S

    July 13, 2016 at 1:24 am

    Vow! What a strenuous but thorough job! Hat's off!

  3. Anthony

    July 13, 2016 at 4:43 am

    Good repair work there by you Albert ! Well done in keeping your patience and a steady hand in repairs like these that really do require these attributes from time to time. As OLED technology begins to emerge over CCFL and LED backlighting methods, perhaps we'll be comparing the difference like candles and light bulbs were in their heydays !
    Thanks for sharing your story and advice here.

    • Albert van Bemmelen

      July 13, 2016 at 3:01 pm

      Thanks Anthony. It indeed is only a matter of time before LED backlights are the standard. It however worries me how little Garbage Disposal Centres or Community Recycling Centres do take good care of recycling hazardous Waste products containing poisonous materials like the mentioned Mercury. I am really worried that up to this moment everything is just polluting our environment. And no doubt are therefore contaminating our Air and Watersupplies. I know that Mushrooms are capable of detoxify polluted soil but I don't see many Mushrooms and it probably needs a big Mushroom factory to detox all that Waste. And neither do I eat them because of that. Cheers!

      • Anthony

        July 13, 2016 at 7:58 pm

        Indeed Albert...mankind does tend to not treat the earth very well at times and hopefully we can all really minimise the impact we have on our precious environment ! I for one am shocked that things like disposable nappies are sold like so many other throw away items and these take over a hundred years to break down !
        Oh well, at least you and the other highly skilled repair technicians on Mr Jestine Yong's website do their their best in saving many electronic devices from the landfill ! Keep up the good work Albert !
        Kind Regards

        • Albert van Bemmelen

          July 14, 2016 at 4:16 pm

          About those disposable nappies Anthony. I once saw on TV that those are very Fire resistant. See for instance:
          Which is probably the reason they last as long before they dissolve.

      • bob

        June 29, 2019 at 1:52 am

        mercury comes from our environment and put into these tubes

  4. beh

    July 13, 2016 at 12:00 pm

    thanks for this article.impressed me

    • Albert van Bemmelen

      July 13, 2016 at 4:16 pm

      Thanks Beh. I do hope to find another big sized Monitor with a such simular defect again for a very low price myself too. Because it has a terrific clear picture through the Glass Plate on the front and the perfect HDMi quality High resolution view. It also had 2 small Laptop Speakers integrated too. I now use a 22 inch Monitor for my Dual Core E3400 Intel PC (A secondhand LED backlit Samsung SyncMaster BX2250) but its vision is not so bright and lesser compared to the Glass view of this repaired HP 2509m.

  5. suranga bandara, Suranga Electronics

    July 13, 2016 at 2:27 pm

    Hi Mr- Albert !

    Great Job You have done.
    good. My Congratulations !!!

  6. Yogesh Panchal

    July 13, 2016 at 8:02 pm

    Albert ,

    Thanks for tips, yes very tedious job and congratulate for saving the monitor from Junk.

  7. Mahmoud

    July 14, 2016 at 8:49 pm

    nice work will done

    My Congratulations

  8. Dale

    December 9, 2017 at 8:37 pm

    My monitor would flicker and then shutdown after 2 seconds. Lifting R29 to change the current level into the ISEN pin of the INL816GN IC allowed the display to stay on. This caused me to replace both T1 & T2. After doing so and reconnecting R29 the monitor was working again.

    Thanks for all your repair tips.

  9. Suemay Gibson

    March 9, 2019 at 12:45 pm

    I read your article and I have the same monitor that recently started flickering.

    Can you email me back if I have a few questions.

  10. Gavin Bryars

    November 14, 2019 at 4:04 am

    I just repaired my own HP 2509m monitor thanks to your article. It had the exact same problem. I wonder if this is a design flaw or bad soldering? Surfing the web, I could see many people having that same flickering problem. Anyway, your help is much appreciated.

  11. Pascal van Nek

    November 24, 2019 at 7:47 pm

    I now want to make it led but I am now looking how to connect


Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Free Report