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).
This is a made in China CRT TV set and was brought to my shop with a vertical deflection problem. Usually a vertical problem is shown on TV screen with a black screen and a line across the screen.
Most of the time, you can turn the TV and you could see the vertical line across the screen but in my case here, the TV was dead. I could not turn it on. The customer told me that a line across the screen came on and then the TV went dead.
I could read the 300 volts on the main capacitor and 124 volts was reaching the horizontal transistor. There was no high tension present and the stand by light was on but the TV was dead. From experience, I have seen it happen so many times that when there is a dead short in the vertical IC itself, it could affect the whole TV and in this case the TV was dead. To confirm my analysis, I checked the 25 volts coming out of the secondary section of the power supply and they were missing. The vertical IC has a dead short in it that it was pulling the 25 voltages down to 1 volts only. How did I know which ACC leg to look for to read the voltages? The only way to know is by checking the specification of the vertical IC online and you will know which leg that is getting the power. In my case, the vertical IC LA78041, leg number two was the power feed to this vertical IC.
The moment I soldered out the vertical IC, power came back to the set and I could see the vertical line across the screen. And I could read the 25 volts on the printed circuit. It is always a good idea to check for bad capacitors around the vertical IC. In my case, I found 6 bad capacitors there. Three capacitors 220uf/35 volts and three capacitors 450uf/16 volts. I replaced all of them.
I replaced the vertical IC and the TV came alive and I could see a picture but there was something wrong with that picture. The blue color was missing in that picture. Usually, there are too things to look for in such a case.
1- The blue color filament in the CRT neck is not working right. Usually there are three light in the neck of the CRT tube. Sometimes you could see them there if you dim the light in the room.
2- The transistor for the blue color in the CRT board is bad.
To my luck, when tested the transistor, it was shorted out. It was BF422. The moment I replaced that transistor, the blue color was restored.
It was lots of work but at the end, I won the challenge and the joy to see that TV come to life was wonderful.
A friend of mine brought this TV to my shop not for repair but to give it to me to use for parts or sell it. He just bought an LCD 32” TV and wanted me to have his old CRT TV. It was a big 29” TV, Korean made and it was really heavy.
I plugged it in and I could hear only audio coming out of the speakers and only a horizontal line across the screen. This is a deflection problem and it cost only about 10 dollars to fix. So I decided to fix that and see if I can sell it cheap.
I opened the cover of the TV and started measuring voltages on the pins of the IC. I could see 40 volts on pin 9. This testing is very important. Before changing the vertical deflection IC, you need to make sure there are voltages reaching the IC. Usually these 25-40 volts come from the fly back transformer. One of the pins of the fly back transformer will give out usually 25-40 volts then it goes through a diode to change it from AC to DC, then it goes through a resister fuse, usually 1-3 ohms 1-3 watts. Sometimes, the fuse resister will be open causing this problem to appear on CRT TV.
The vertical deflection IC TDA3654 is very easy to find on board. It has a heat sink and usually it is very close to the Yoke sockets. I could not find TDA3654 in the electronic shops around me but instead, I put a TDA3653.
I replaced the bad IC with the new one but did not turn on the TV yet. It is very important to check the capacitors around this IC. Sometimes bad capacitors cause the vertical IC to go bad again. Check the capacitors before turning the TV on. I found two bad capacitors that had a high ESR reading. It was a 1000uf/25 volts and 100uf/25 volts.
I turned the TV on after connection a picture/Audio source. The sound was great and the picture was great. After five minutes, I could see horizontal lines on the top of the screen and the picture started shaking. Usually this is a capacitors problem and based on that, I started checking the capacitors in the power section area and the vertical deflection area as well. Found some bad capacitors there but it did not solve the problem. I touched the IC with my finger and realized that the IC was getting hot causing this problem to show on the screen. I used the hair dryer to make the IC hot so it will speed up the repair time. The problem got worse as I was applying hot air to the IC. I applied cold air to the IC and the problem disappeared. There was something wrong with the IC.
I started studying the specification of the IC I replaced. The bad IC TDA3654 is the original one and it can handle temperature 90-110 C but the TDA3654 can handle only 90 C degrees. It does make sense, once it got hotter; the IC was acting up showing this problem on the screen.
I looked for the original TDA3654 and found it, used one actually. I replaced it and I tested the TV for more than three hours and it worked nicely. It was a long repair time but was not wasted in vain. I have learned a few things, but most important, I know now that TDA3653 is not a replacement for TDA3654.
A dead CRT was brought to my shop by a friend of mine. He said that this TV suddenly stopped working. I could see a stand by light but there is no high tension sound, no audio and no picture.
I took the cover off and scanned the area for bad capacitors and found no bad ones. I plugged it in and started testing voltages in the power section area. There was 300 volts reaching the main capacitor and there was 24, 110, 10 volts coming out on the secondary diodes in the secondary power section.
A dead TV set was brought to my shop for repair. There was no stand by light. Usually that is an indication of a problem either in the fly back and the horizontal transistor in that section or the power section of the TV.
Upon opening and checking the voltages at the high tension area, I found out that there was no voltages reaching the horizontal transistor. I unplugged the TV set and checked the horizontal transistor while on board with a multi meter set to diode setting. The meter gave me a continuous beeps on the three legs. That gave me the indication that the horizontal transistor was shorted. I soldered it out and checked it again. it was D 1555 and was a shorted transistor.
I used the light blub trick which is connecting one wire of the light blub to the collector on board and the other wire to ground and turned the TV on. The light bulb came on and I got a reading of 115 volts at the horizontal transistor. I replaced it with a new one and turned on the TV. It worked for while but I started seeing blue sparks in the TV screen. At first I thought it was a problem with the fly back transformer and I started doing some checking in the high tension area but all the parts there checked Ok.
There was one thing left to do and that is to replace the fly back transformer itself. I looked and searched for one in my electronic junk bile and found a good working one. I installed it and turned the TV on and the same problem happened, blue sparks inside the screen. Conclusion: that was not a fly back problem.