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Discussion Starter · #1 ·
I may be posting this prematurely as I’m still trouble shooting but maybe someone has already seen this and can provide an answer faster.


Originally I stole a set of RGBHV cables off the LCD projector at work. These are some of the cheapest cables I’ve ever seen, probably built onsite by some AV gurus who specialize in installing LCD projectors in conference rooms for 800x600 computer graphics. They do however work ok and produce a stable picture on my 1271.


This weekend a friend of mine, who is an engineer for one of the national TV stations, sent me a set of HDTV quality RGBHV cables he makes on a regular basis for the station. These cables are made using Belkin 1505a cable which seems to be a fairly decent cable.


I hooked the cables up and after about 45 seconds I noticed the picture starting to go. It was streaking and becoming very unstable. About 20 seconds later the whole picture was rolling. It had completely lost sync.


Troubleshooting so far…

It’s not a bad cable in the set he sent me. It happens if I swap his cables all around.


It does seem to a problem with only the H-sync. If I swap out just the H-sync with the cheap stolen cable then the picture will stay stable for an entire movie.


My guess is there is an impedance problem (not 75 Ohm) on the H-sync but I didn’t have my meter to test. My friend suggested I get a 75 Ohm terminator and T connector and plug that into the H-sync.


What else could this be? Have you seen this before? Could it be a problem with the IFB-11 (iirc I think I have an 11) input board?


Thanks for your guidance.
 

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I dont understand what you mean by swapping cables all around? You mean like using the blue for the H sync and H sync for blue right? If that is the case ten you might be right about the 75 Ohm problem.


In most cases cheepy cables will work for video but not the sync. How long a run are these cables? I woudll think if your friend is an engineer though he would have used 75 Ohm cables. Either that or there is a polarity problem but if he used solder on ends or crimp ends I cant see how that could happen.
 

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Discussion Starter · #3 ·
I agree about the sync which is odd that the cheap cables hold sync but the expensive ones will not.


Yes, what I mean by swapping all around is take the blue, move it to h-sync, take the red move it to blue etc.


My friends cables he sent are 25 feet. The cheapy cables are closer to 20 feet.


He used 75 Ohm crip connectors and the Belkin 1505a is a 75 Ohm cable.
 

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Discussion Starter · #4 ·
I just spoke with my scaler vender and they think they know what the problem is. They are sending me 75 Ohm inline terminators for the H and V syncs. I'll test those out and see if it fixes it.


Looks like the cheapy cables are so cheap and there is such loss the problem fixes itself.
 

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Funny you should bring this up...

I have been using a rbghv 75 ohm digital cable from liberity from my extron to my 1270q, I bought the cable bulk so I used some cheap bnc ends, The cable work great... Then I got a bug in me to replace then ends with liberity 75 ohm bnc ends, so I ordered 10. My freind has the "special tool" to install the ends, but when he did, he put 6 on one end and I came up short on one side....

Well unit I can get acouple of new ones for the other side I am running with rgb with sync on one cable. At the pj I plugged in all of them thou rbgvh... the other side of the cable one was unterminated... The pj would loose sync like crazy!!! until I unplugged the unterminated end. Then It sync fine...



Brian
 
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