Need Help - 720 Monitor Sync on a Neotec NT-2501

tparis

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Hi all,

I am doing a monitor swap on my 720 and replacing the old 25k5155 with with a Neotec NT-2501.

There was a post a while back that discussed my exact situation however I am not quite understanding the proper wiring configuration from the post.
http://forums.arcade-museum.com/showthread.php?t=78123
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pin 6 on the 720 video PCB, has composite video sync! The problem is that the harness has no wires running to this pin on P19 pin6. So I replaced the connector, and added the pin 6 and ran it to the monitor video connector. On the monitor I removed the horizontal and vertical Sync wires, and placed the composite sync in pin 6 of the video cable going to the monitor. Problem solved!
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So the molex end that plugs into the NT2501 from the 720 has 6 wires.

As prescribed in the previous post I am to remove h sync and v sync from both sides of the video molex; pins 1-2 (monitor end) & 7-8 on the (PCB end) - Then I am to connect to pin 6 (composite sync) on the PCB side and send it to the monitor end of the molex? This is where I am confused.
Do I send it to what would now match up as video on the
NT2501 which would be #2 on the molex?

Also pin 3 on the 720 monitor side molex would now be matching to the ground pin on the NT2501 schematic. The gnd is thowing me off as well.

New at this and would greatly appreciate some guidance.



video-sync.jpg

 
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i think according to your drawing it should be pin 1 the S.H that the composite sync should go to.
 
Thank you so much for clarifying. What about the ground pin on the neotec? Will this be an issue with the 720?

ground (gnd) and videortn (video return) both are grounds.
 
what was wrong with passing separate syncs to the neotec?

I couldn't get it to sync using separate syncs, then I put the h&V sysnc on pin 1 and I couldn't get it to sync either. Starting reading more about this and found others with the identical issue and having to wire up pin 6 form the PCB which is composite sync.

So like another person that said he solved the issue he ran a wire from pin 6 of the 720 PCB which is composite sync to pin 1 of the molex end that plugs into the monitor.

I have tried all this and I still get no sync. I am positive the monitor works because it was on the bench yesterday looking beautiful.


20160926_131211.jpg



Below are using pin 6 from PCB to pin 1 of NT-2501


IMG_2765.jpg


IMG_2764.jpg
 
Well now the screen is dark and the monitor is making a chirping noise. Sounds like it's going into a shutdown loop.!! $%^&$%^$!

Need to fix that then back to figuring this wiring out .
 
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Neotecs are apparently "easy" to work on. I wouldn't know, I lump them in the Asian shit category and haven't bothered with them. what I do know is you need fresh caps on them. otherwise they'll eat HOTs like popcorn. there's a resistor you measure B+ at, I can't remember the exact value it should be set at, but I want to say it's 122V. then as soon as you dial the B+ in, you have to turn the shutdown pot until the monitor turns off, then ever so slightly back off on it so it'll run, but if the B+ climbs any it will shut off.

this will save you a HOT (or many).

I have capped a 3501 before. I wanted to kill myself. I was glad I saved the K7500 for last that day; that didn't hurt as bad as it should after that Neotec.
 
Thanks for the info. I'm getting a rebuilt 25k2515 so measuring the resistance of each monitors coils so maybe I can do a tube swap. Then I don't have to change the wires on the 720 and I can also fix the Neotec.
 
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