A dead Elbit CRT TV repair. Model EC70-602-CTI
Two of these TV sets came to my shop and both of them had the same problem. Both were dead. When plunging both of them in, I could hear a ticking noise coming from inside the TV. I had to open the back of one TV set to find out what was wrong with it. In this case since both has the same problem, if I am able to fix one of them, there should be no problem fixing the other one. So, let us get started.
When taking the cover off, I scanned with my naked eye for bad electronic component but I could not find anything. From experience, when I hear a ticking noise coming from inside the TV set and the stand by light is not on, one thing comes to mind; the problem is in the high tension area. My focus now is in that area, mainly, the Horizontal Output transistor (Hot).
I measured the output voltages at the secondary section of the power supply and the 145 volts were missing indication a problem either in the way to the Horizontal output transistor or the HOT itself. I went directly to the HOT and measured the voltages there and I was not shocked that I could not read any voltages there. The moment I de soldered the collector leg of that transistor and added a light bulb to the point, the light bulb came on reading a 145 volts and that was a very good sign. Also the ticking noise was gone and I could see the stand by light coming on. The TV set will not come on until you replace that shorted out transistor.
I de soldered the transistor out and checked it with the ohm meter. All three legs on that transistor were shorted out indicating a heavy short in that area. When I asked the customer about that TV set, he informed me that the electricity in his house was going on and off for more than three or four times, causing a heavy load on that transistor and eventually shorted out. The part number of that HOT was BU508A. It was an 8 amp, a 135 watts transistor.
I replaced the transistor and fired up the TV set and it worked fine. Was glad to see that but I was not glad to see another problem in that TV set. The Audio was missing which meant the challenge was not over and I have not won my crown of repair satisfaction yet.
Sound was missing and the most logical answer is to go to the sound IC to make sure it was working fine. Checked the voltages and there was no reading there. That tells me the sound IC is good so far. I need to get these voltages reading back then I will see if the sound will be restored or not. The part number is TDA1521 and the 7th leg is the voltage input on that IC. I traced it backward to the main source which was the main power supply. As I was tracing back, I could see a lot of bad soldering joints and I re soldered every bad joint on that board. I turned the TV set back on and guess what, the sound was restored. The crown of the repair satisfaction was accomplished and I was happy to see that TV set comes back to life.