Just a quick teardown today – we’ll be looking at a Soniq QV320PH 32″ Plasma TV which has faulty audio – no sound, it seems to turn on and display images just fine. I opened this TV to see if I could repair it and in doing so I didn’t end up taking close ups of the chips.
After a lot of screws we’re in.
1. The main board contains all the processing power, RAM, Flash, TV tuner, audio amplifier, etc.
2. The power supply board
3. The plasma screen drivers
Upon inspecting all the boards it looks like 2 capacitors have blow on the power supply board.
The caps were replaced but it didn’t fix the audio issue.
I powered on the TV with the back cover removed and noticed a lot of heat coming out of the chip that was mounted on the case – probably why it was mounted right? I tested the input and output, 15V going to 1.5V which didn’t seem right at all. I measured the temperature using a cheap IR sensor I got off Ebay and it read somewhere along the lines of 120C. I found that the chip is an LM7812 voltage regulator, the output voltage should be 12 volts so something is very wrong.
The input of this voltage comes from the power board and output is feed into the main board – the main board also indicated that this rail was meant to be 12 volts. I unplugged the regulator and the output was 12V, plugged it back in and it went back to 1.5V so there has to be a short somewhere. Looks like the 12V feeds the large capacitor and then into this chip. I tried replacing the capacitor but no change.
The chip circled is the Yamaha YDA138 Audio Power Amplifier and the two connectors on either side are the speakers, tested both of them by connecting a 9V battery and they work. I continued to test different points within the circuit, it seemed that the 12 volt rail was shorted to ground but unfortunately I wasn’t able to determine what the cause was – I think it could be the YDA138 but I couldn’t find any available for sale.
I just ended up unplugging the voltage regulator and the TV still works but with no sound as before – can just use external speakers. At least now the TV should last a bit longer with the 2 caps replaced and since the short circuit / voltage regulator was removed it shouldn’t put more load on the power supply.
Edit 18 Jan 2015 – The TV’s audio has now been fixed looked into it again due to a comment, it was a 10uF MLCC on the bottom.
You can get the YDA138 via eBay: http://www.ebay.de/itm/YAMAHA-YDA138-E-SSOP-10W-Digital-Audio-AUDIO-power-Amplifier-IC-/261047558751?pt=LH_DefaultDomain_0&hash=item3cc7a5a25f
Or you just buy one of these (http://dx.com/p/y148-audio-amplifier-module-93121) modules and mount it inside the case.
Hi, thanks for that, I should have checked Ebay! Now that I know I can buy it I might try de-soldering it to see if it’s the problem.
On your red circle, just to the right of the connector (near your red “+”) there is what looks like a scratch or something crossing the two power traces. What is it and might it be causing the short?
I took another look, it was some of the glue that they used to keep the connector in place.
Sorry if I sound like Captain Obvious but the tab of the 12 V regulators is usually GND (ground). I see an insulating washer, I see some thermal paste but I don’t see if there is a mica foil or another insulator present..might be that the board or something else touches the positive voltage and the regulator completes the short.Try insulating it and see ( use mica or other insulator between a new 7812 and the base board, and be sure to re-apply paste). Does the yda 138 work when powered from an external supply?
Hi Axel,
I took another look at this since this TV is now a spare, the 7812 GND is connected to the board, I removed it from the board but the output still dropped to 2.5V. I tested the 7812 on it’s own and it did 1.5 amps without any issues. Measuring 12V to GND gives me 20 to 40 ohms (when reading 40 ohms, it slowly starts dropping down). I need to try the YDA on it’s own sometime.
Edit: Removed the YDA and the 20-40 ohms remains on the board. Maybe a MLCC on the bottom.
Edit 2: Yep have confirmed it was one of the MLCC caps – 10uF. Replacing it has fixed the 12V rail but still no audio
Edit 3: I’ve just removed the board and re-connected all the connectors and now it’s all working again with audio! 🙂
Hey…i hv one soniq wth me…family was watchng tv n suddenly the picture disappeared!!! The audio was normal bt cnt c anythng…wat wud the the problm??!!