How To Repair LCD Monitor Flicker- HP2509m
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.
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).
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…).
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.
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.
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!
Until another Fix !
Albert van Bemmelen, Weert, The Netherlands
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Note: You can read his previous repair article in the below link: