本文是转载来自外国网站上的文章(This article is shared from the foreign website)原文链接（the original article link）：http://jestineyong.com/useful-rt ... r-in-lcd-tv-repair/
故事发生在欧洲的荷兰：
Useful RT809H Universal Programmer In LCD TV RepairAbout a week ago I noticed an older used (2010) 26 inch MEDION LCD TV that someone had thrown outside next to our building’s waste container. And before I took it home for parts or for repair like any good engineer would do, I first checked if the MEDION TV model MD20174 was not too damaged, and luckily the LCD screen looked still unscratched and repairable. I cleaned the dust from the outside case before I checked if the TV was still functioning somehow when powered on. By switching ON the power switch on the back and pushing the Standby side button the screen came on. But only for a short few seconds after which the TV didn’t react anymore on the buttons or the power switch. No matter how often I had tried. So it was time to open up the TV to examine what had caused this. I also checked the internet forums and searched with Google for any answers that could help fixing this older MEDION TV. But nothing could be found. Not even a schematic and certainly no service manual. I therefore started to check with my DMM the voltages on the power supply board type AOYUAN AY130P-4HF03/04. All voltages checked out fine. So I continued by checking all flat cable connections and how they were attached to the other boards. On following picture all connectors are shown. It shows that the four 24V power lines and the 4 GND lines (CON3) go directly to the CFL inverter board. The CON2 connector of the power supply is not used and the other connector with the four +5V power lines, the five GND lines, and ON/OFF plus +5VSB (5V standby) all go to the MAINBOARD. (Next photo shows the power board connectors).
Because I knew that I could try to extract the mainboard’s firmware with my new great RT809H universal programmer, even if the TV wasn’t giving any signs of life, I first decided to make sure I had a backup copy of the Medion Firmware of this TV. Because if the FW is lost the device will be beyond any repair and will not operate anymore. And Medion doesn’t share this with TV buyers/owners on the internet. Only a Medion MD20174 users guide can be found and downloaded. Above backup method is simply possible because the BIOS chip on the mainboard can be read through the VGA ISP port of the RT809H when connected to the VGA port of this TV. The BIOS chip, here a 4MB eeprom, always gets 3.3V on its power pin 8 and so can be read even if the GPU/TV mainboard chip is partly defect. I didn’t find any help or information but assumed that it was not the LCD, the inverter, and neither the CFL backlight tubes that were at fault, because I had seen them working once. Showing a perfect TV picture if only for a few seconds before the screen garbled and the TV kept silence afterwards. And that only left one possible suspect open, the mainboard. The mainboard is also the board that controls the BKL, ADJ and GND lines on the CFL inverter board. I checked the inverter board which contained a SOP 24 pin Samsung SEM2106 CFL controller chip with a 5A onboard fuse. And all inverter board components looked fine so I ruled out that it was defect. Only the mainboard that is the working motor behind all functions of this TV could be causing this defect. Next screenshot shows that I was fully able to read, auto verify and save the MX25L3205 serial eeprom on this TV’s mainboard to my computer. With this great RT809H programmer we also simply can delete the BIOS chip of TV’s and Monitors with the VGA ISP connection, completely remove the FW after which the device no longer operates, and then write the FW back to the internal chip (without even having to open up any device!), and we’ll notice that the TV or monitor works again afterwards like nothing happened! But of course make sure that you read and saved the Firmware first!
I was convinced that only the mainboard was defect and was afraid that hot fixing would not make any difference if the GPU/TV mainboard chip was damaged. Same problem is often the reason that many laptops do not give any visible LCD screen anymore. And in those cases only the external video port may still operate on external monitors. But even that is no certainty if that video chip or its mainboard memory are internally damaged. Reballing and/or replacing any defect chips would make sense but is a very tedious job without any warranties on success at all! Luckily to my surprise I found a seller who still sold a used but good working mainboard. These Medion TV boards are apparently also known as Foehn & Hirsch FH-26LMH – Main AV – MSD306V4.0-A (MSD306V40A) boards. And for 25 Euro and 16 Euro shipping costs I only waited 2 days on my replacement board. Which today arrived and of course was immediately tested. The MEDION MD20174 came indeed back to life and the repair was a great success! Without the IR control (which likely was still kept by the previous owner) my Dreambox DM800HD se with super Japhar SIM OpenPLI6.0*** was connected to the scart port and the TV showed some great screens of which I will add a few screenshots after following mainboard photos (Top and solder side). Following photo shows the top left side of the mainboard.
Next photo top mainboard side with the GPU/TV chip top left and the DVB-T tuner right below. Photo below shows mainboard bottom/solder side with model/version labels. Next photo more closely shows the components on the TV mainboard. With step-down mp1582en. Bad news is showed on TV by beautiful ladies to make all misery bearable. In previous photos also three LM117 regulators are visible on the mainboard component top side. Thank GOD for creating la femme and making electronics possible! After this repair only a small white point on the left part of the screen marks the spot where the outside screen was slightly damaged by the previous owner but with such beauties it is hardly noticeable. And nothing is perfect although above ladies come extremely close! Until another repair!
Author: Albert van Bemmelen, Weert, The Netherlands.
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发表于: 2018-11-15 10:16:58
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