This LCD seems to have a problem with the main power supply. When it is plugged in I get no power led, and no dc voltages at the connector to the logic board. I have tested the large cap by using an analog meter set to 600v AC and up, and placing the black probe to the '-' pin, and the red probe to the '+' pin and it reads about 340v. Then I tested the leads on the transformer by putting the black probe to ground and the red probe on each pin of the transformer, and every pin on the primary side shows 26.2v AC, and every pin on the secondary side shows 25.7v AC. I also get 26.2 v AC on all pins of Q902. I removed the transformer and tested it with the ring tester and when putting the probes on the primary side, the outside pins, I get all green lights (meaning very good). I get nothing on the secondary side. One other thing to note, the large cap discharges very slowly after unplugging it. Like several minutes or more.
I have replaced all the caps except the very large one, and the two larger ones on the right side - I did not have any replacements on hand. But I tested those two with ESR meter and they were ok, but nearing the threshold.
Any ideas about what might be wrong?
Secondly, I am trying to get a handle on testing transformers with a ring tester. I did some reading and one place said that on the main transformers on the LCD, the step-down ones, that you can only test the primary side, and to follow the trail from the + side of the large transformer to one pin, and the trail from the transistor to the other pin to know where to put the leads of the tester. Then for the inverter or step up transformers it said you could only test the secondary side (the side toward the ccfls) and didn't say how to tell which pins to use. Is this correct? If so, do you assume the side you can't check is ok?
One other item on the power supply, how come when I test the AC voltage at say the main fuse, or even at the + terminal on the plug it reads less than 120v? I haven't made any notes, but I think it it usually less than 35v.
Thanks.
I have replaced all the caps except the very large one, and the two larger ones on the right side - I did not have any replacements on hand. But I tested those two with ESR meter and they were ok, but nearing the threshold.
Any ideas about what might be wrong?
Secondly, I am trying to get a handle on testing transformers with a ring tester. I did some reading and one place said that on the main transformers on the LCD, the step-down ones, that you can only test the primary side, and to follow the trail from the + side of the large transformer to one pin, and the trail from the transistor to the other pin to know where to put the leads of the tester. Then for the inverter or step up transformers it said you could only test the secondary side (the side toward the ccfls) and didn't say how to tell which pins to use. Is this correct? If so, do you assume the side you can't check is ok?
One other item on the power supply, how come when I test the AC voltage at say the main fuse, or even at the + terminal on the plug it reads less than 120v? I haven't made any notes, but I think it it usually less than 35v.
Thanks.
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