Strange conductive goo wreaks havoc on my girlfriend’s TV.

By | May 16, 2018

For a few weeks now, my girlfriend’s TV has had an issue where any remote, or any button pressed on it’s remote would make the volume go up. Pressing the volume down button would result in the volume going down one notch, and then going back up one notch. Holding the volume down would make it turn down, but very slowly because it was still trying to turn up at the same time. It was still watchable and I didn’t have a loner TV to let her use, so we decided to wait on any potential repair. There was even a time when the issue went away for a couple of days. Then, a couple of days ago, the problem became worse and the TV unwatchable. It was now turning up to 100, and nearly impossible to turn down. Even if she could get it to turn down, it would go right back up within a few minutes. I removed the back yesterday and was surprised to find a brown oily substance coating the inside of the plastic back panel.

At first I thought maybe something had been spilled in it when she moved, but she said no. Ultimately, I determined that the goo had leached out of the plastic. My reason for believing this is because I noticed the plastic had bubbled in a few places. This TV, a Haier LE46A2280, had sat in a steel Uhaul storage locker for about two years, with no climate control. I don’t know if that had anything to do with this, but it’s at least something to consider.

I took the TV to my shop and began troubleshooting. The first thing I tried was removing the key control board. I’d noticed it had the oily goo on it, and the particular issue made it a potential suspect. Even with it removed, the problem persisted. I looked at the IR sensor board but it looked fine. I tested the capacitor and two short chip resistors, and they were fine. I also tried replacing the IR receiver on the board with one from a different board. The problem was still there. I looked at the main board, even desoldered and removed the metal shield over the CPU, but couldn’t find anything wrong. At least nothing visual anyway.

Finally, I started thinking about the possibility of some of the wires in the IR sensor harness being shorted together. This is when I discovered that some of the goo had dripped onto the connector which plugged into the IR sensor board, and that it wasn’t just goo, it was conductive goo.

As you can see in the picture, the orange, white, and yellow wires have a lot of the goo on them. The resistance varied between 1MΩ and 20MΩ. The higher of the resistances was between the white and blue wires. The lower between white and yellow or orange. After taking the above picture, I removed all the wires from the connector so they could be cleaned. Using a toothbrush and some 91% isopropyl alcohol, I scrubbed all the conductive goo off. It was quite stubborn in some places such as the inside of the connector. A piece of paper towel rolled to a point helped with that. When I was satisfied that I’d gotten everything clean enough, using the picture as a reference, I put all the wires back in their respective holes. Now it was the moment of truth. I reconnected the IR sensor board, plugged the TV in, and pressed power on the remote. It turned on. So far so good. Next, I tried the channel buttons. I haven’t reattached the key control board yet, so everything I’m doing is on the remote. The channel buttons work, and more importantly, the volume is no longer changing when I press them. Finally, I tried the volume buttons and they worked as expected. That goo in the connector was the cause of the strange behavior.

It wasn’t quite done yet though. I’d noticed that a few resistors on the key control board looked really bad. Two were supposed to be 3kΩ, and one was supposed to be 20kΩ. Upon testing them, I found them to be very high in the MΩ scale, like around 20MΩ and higher.

 

I don’t have a lot of SMD resistors in stock. I usually just order as needed, or find a used one on a scrap board. I was able to find the 20kΩ resistor, but not the 3kΩ ones. I did however have some 1.5k through hole resistors. First, I put some Kapton tape on the edges of the board where the leads would wrap around. I did this to eliminate the possibility of them shorting with the edge of the copper on the top and bottom of the board. Then, I soldered together two pairs of the resistors to make the 3kΩ I needed. I fastened them in place with some hot melt glue, wrapped the leads tightly around and trimmed them to the correct length. Finally, I soldered the leads to the SMD pads. I made it work with what I had at my disposal, and the important thing is that it did in fact work.

To prevent this from happening again, prior to reassembling the TV, I cleaned all the remaining conductive goo from the inside of the back panel using dish soap and an old rag.

 

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