Add philips 42inch repair project

content/projects/repair-philips-42pfl6057h-12/index.md

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+date = "2019-02-10"
+title = 'Repair: Philips 42" 3D LED TV with Ambilight'
+tags = ["repair", "audiorepair", "philips", "tv"]
+categories = [ "Audio Repair" ]
+summary = 'Last week I started a new repair project: a 42" Philips TV. The power supply was obviously defect, but I ran into another problem as well...'
+[image]
+  focal_point = "Center"
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+
+I've done the occasional television repair in the past. Mostly Philips TVs with the '3 blinks' problem. When the power supply of a
+Philips TV is defective, the main board will detect this and blink the stand-by led 3 times to indicate this problem. Power supply issues
+I can fix - mostly. 
+
+So, I found this Philips 42PFL6057H/12 TV on Marktplaats. Instead of the '3 blinks', this TV did absolutely nothing. Another clue that
+the power supply is probably toasted. 
+
+## Step 1 - Open it up
+
+First thing is to remove the back cover of the TV. There are a dozen or so screws on the back. These, together with two cables for the 
+buttons and ambilight, expose the power supply board and main board. 
+
+The exact workings of how a Philips TV boots up when power is first connected is a bit more complex than what I'll describe here (read the service manual if you're 
+interested). When the power cord is connected, the power supply will generate a 3.3V stand-by voltage. This is enough to power the 'Fusion' chip 
+on the main board. The main board will then signal the power supply to start the 12V rails. 
+
+So, the first order of business is to check if the 3.3V is there. It wasn't. Careful probing revealed a shorted dual-diode package. Luckily, I 
+was able to replace this part, as another power supply board from a previous repair had a similar dual-diode.
+
+This brought back the 3.3V, but now I _did_ get the 3 blinks, as the power supply was not able to provide 12V. Some further investigation 
+revealed that one of the control ICs on the power supply board seemed damaged as well. This part is hard-to-get and I opted to purchase
+a replacement power supply board. 
+
+## Step 2 - Why won't it work!?
+
+With the power supply board replaced, I could measure 3.3V and 12V from the power supply. However, the stand-by LED wouldn't turn on. 
+The TV _would_ respond with a blinking LED when I used the remote control on it - but it would _not_ turn on. 
+
+Some googling revealed that this is a main board defect and can't be repaired. It's recommended to replace the main board. 
+
+Well, I already replaced the power supply board, and I really didn't want to add further costs to this repair. Looking at the 
+main board, it's not very complicated. There are some peripheral connectors and support ICs, an audio section, and this big
+BGA Fusion SoC. It's heatsinked on the front. On the back a piece of thermally conducting foam was used to sink some heat into the
+metal chassis of the TV.
+
+So - nothing is obviously burnt. The TV does power up (so the Fusion SoC must be doing _something_), but it won't turn on. 
+
+If there were to be a problem, my guess would be that the Fusion SoC suffered some thermal stress and any one of the BGA
+connections might have been damaged. 
+
+BGA (Ball Grid Array) is quite simple. The IC and PCB have solder pads and you sandwich small balls of solder between 
+them to make an electrical connection and secure the IC in place. This works great for SMD assembly of ICs with a 
+high pin count. 
+
+One problem is thermal stress. When the IC generates heat, the PCB expands - and shrinks again when it cools off. In 
+the long run this may also cause stress to the miniscule solder balls.
+
+I found this photo on the internet that shows the exact problem. I don't have the equipment to inspect BGA's like this.
+
+![A cracked BGA solder ball](./bga-cracked.jpg)
+
+## Step 3 - Reflow
+
+At this point the main board is unusable. I can either replace it or attempt to fix the possible solder ball issue I 
+suspect. 
+
+Feeling adventurous, I removed the main board and powered up my heat gun. I have one of those (cheap-ish) soldering
+stations that come with an old fashioned iron _and_ hot air. I removed the heat sink and started carefully heating
+up the IC. I tried measuring the surface temperature of the IC with my infrared meter, but I did not measure 
+above 160°C - too low to melt solder. Then I noticed that the solder on nearby resistors did melt. 
+
+![The actual Fusion SoC](./fusion-soc.jpg)
+
+I stopped heating the board and let it cool for a few minutes. Re-installed the board and all the cables. Plug
+in the power. Press the power button. And there it was. A working TV.
+
+## Step 4 - Cleaning up
+
+The ceramic heatsink on the Fusion SoC was attached with adhesive heatsink tape. It didn't stick. Luckily there
+were mounting holes around the IC, so it was easy enough to construct something to keep the heatsink firmly 
+attached. 
+
+Next, reinstall the back panel and reconnect the Ambilight cable. And I've got a new TV :-) 
+
+![Working TV](./featured.jpg)