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Discussion Starter #1
Hi all,
I have a Hitachi rear projection HDTV Model 65t500 about four years old. A couple of weeks ago while watching it the magic focus started to try reset the convergence. I had to manually stop it and then reset it manually to get it back. The next day it did the same thing again. After I readjusted it this time and seeing some info about the convergence IC's I opened the back of the set and took a look. I cleaned some dust away from the IC's and rerouted some cables that was in the way of the air flow and all seemed to be well. About a week later I noticed that when I try to play a DVD at 720p or while tryiong to watch a HD signal the picture would not sync. All I got was scrambled video. Thinking this may be a problem with the cable box I am using, the cable company came and replaced it with the same results. The tech said it was my tv. Now when I try to go to the magic focus it does not even work at all. Pushing the magic focus button does not even bring up the crosshatch pattern. The picture is still great and in convergence at 48oi but in any other definition it won't sync. My question is therefore could the convergence IC's have failed and still the picture be good and seeminly in convergence at 480i and secondly could they also cause the loss of HD signal sync or is it two different problems.
 

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Convergence IC failure would not cause the magic focus to start. This is likely a bad switch or a problem in the system control circuits. You should verify that your set is supposed to sync to 720p. IIRC it only did 1080i and 480 rates.
 
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Discussion Starter #3
Thanks lcaillo,
Okay then assuming the convergence IC's are good what do you thing the problem could be that I get no HD picture and only receice 480i. There is no HD tuner in this set so I have to have a cable box which like I said was replaced with the same result. Do I need to replace the signal board.
 

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I010, HD74HCT245AF, 3.3 to 5.0v level shifter, part number CK38491R would be the suspect. I would change this before board swapping.
 
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Discussion Starter #5
Okay so you think this buffer would be suspect. You think this would give a good 480i picture but loss of sync on anything higher.
 

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It could tie together the two seemingly different problems of starting the convergence program and lack of HD. I have in my records a similar problem which had this as the cause.
 
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Discussion Starter #7
Okay lcaillo,
Thank you very much for the help. That IC is on the signal board so it seems to be a possibility. Now the next step is to see if I can buy this part somewhere and replace it and see what happens. Do you have any idea where I can buy it. I will let you once I get it if that solves the problem.
 
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Discussion Starter #9
Thank again,
I will try to get the part asap and let you know how I make out when I am done. It will probably be a couple of weeks.
 
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Discussion Starter #10
Hi lcaillo,
I have found a place to get the part you said to try. The only thing is I took a look at it on the board and it is quite a small surface mount ic. Have you had any luck removing one of these chips before and replacing it with just a ordinary soldering iron or does it require special tools and equipment. It seems like it would be awfully hard to do without doing more damage. Maybe I will have to leave this to the professionals.
 

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I have no problems, but I have been doing this for years. I suggest melting a large enough blob of fresh solder to cover all the pins and then when you melt it, lift the chip off the board. Then wick up the excess.
 
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Discussion Starter #12
Thanks lcaillo,
By the way in looking at the manual I see there are five led's on the p.s. board. I noticed that they are all lit green and red as usual but when I shut off the power the 5.5v led goes out instantly but the others slowly lose the brightness. Could this be significant.
 

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I don't recall if there is enough capacity in that supply line to hold the diode on like the others. It would only be meaningful if someone has a properly operating set to compare.
 
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Discussion Starter #14
Hi lcaillo,
I just wanted to thank you again for the advice you gave me. You realy know your stuff to diagnose such a problem without even seeing the set. You were right that the Io10 chip was faulty on the signal board. I must confess though that I had a tech install it for me because I didn't have the tools nor the skill. The set works fine now and I am happy. I used to design circuit boards for a living and I have some electronic knowledge besides that, but I can't seem to see why that chip would cause the seemingly unrelated problems. If it is not too much trouble could you please explain.
 

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Have you looked at the circuit? What makes you classify it as "seemingly unrelated?"
 
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Discussion Starter #16
Okay Isee it now. Al those functions pass though that chip. Tell me what does the letters "fc clk" stand for on pin 18.
 

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Not sure, but likely a clock line.
 
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