K7500 in a Atari 720

local413

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I rebuilt a very nice k7500 for a collector who wanted it for his 720. His monitor has been rebuilt a few times and the tube is pretty burnt, so it was time for a replacement.

The issue we're having is the sync. The vid connectors from the original monitor and the k7500 look to be the same, but it must be missing composite video?

Could someone point me in the right direction? I've researched this a bit and can only find info on someone trying to install a neotec monitor and not a k7500.

Thanks!
 
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Take a look at the schematic. By default in most of the System 2 games I've come across, Atari wired up the H an V sync, but not the Composite Sync. Add the Composite Sync to the harness and you should be good to go.

If that doesn't fix it, take a picture so we can see what you have.
 
Will do!

Does 720 just have a typical video cable? As in two connectors?

Game is a few hours away and I'm just going to mail him a new vid cable with added pin.

Thanks for your help! It's tough trying to diagnose a monitor via text and email :(
 
I don't think so.

Also, the sync wire may not be in the main harness coming from the PCB so depending on what you are sending it may not work.
 
Since I'm not at home right now, I don't have pics of it, but the end that connects to the chassis looks exactly as pictured in this thread:

http://forums.arcade-museum.com/showthread.php?t=174474

5504003550_f141e8651d_z.jpg


Here's it installed in the K5515 in my machine (old photo I just found on my photobucket account)

IMG_1029.jpg


Unfortunately, I don't have pics of the other end of it right now. I'll see if I can dig any up or take them tonight.
 
Okay, here are pics from my game:

Chassis end:

IMG_267050.jpg


Video board end:

IMG_267750.jpg


IMG_267250.jpg


IMG_267650.jpg


IMG_267150.jpg


Hopefully this will help someone.
 
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Yeah, what he said. It was repaired and recapped by Chad a few years ago. The tube then started pulsating, I replaced the flyback, seemed better for a while, but not great. There's always been a fair amount of burn in it. It's started flickering lately due to some little sparky thing under the fly...probably a bad soldering job or something on my part. in any case, this med res tube has never looked med res, so it's time for an upgrade.
 
Jedidentist I didn't realize you were the same collector local413 was talking about. So, from your pictures you can see that /Comb sync isn't connected to pin 6 of the connector on the 720 PCB. That is the sync you should use for the 7500 monitor.
 
Ahh.. It's all about who's cool and who isn't.. I get it :)

Sorry about that, I thought he was just adding example pictures for you to see and you were taking it from there. But since he was adding pictures and still talking about I assume you guys weren't sure.
 
We were figuring it out (mainly Local was), but it never hurts to hear other's opinions. I just wanted to post pics publicly in case someone needs them in the future.
 
Okay, I just had a few minutes to look more closely at this. Coming off the video board at the 6th pin is the "composite sync". In the original harness, that spot is left open, so you can slide an 18 gauge wire in there into the existing connector. On the monitor chassis end is where I don't know where to connect it. On the k7500 schematic/manual it lists position 5 on the chassis as "+- horizontal/comp sync", which is wired to the "horizontal sync" on the video board. Position 1 on the chassis, which is not connected to anything is also labeled as "+- horizontal/comp sync". Is that Position 1 on the chassis where the "composite sync (pin 6)" on the video board should be connected? I gave that a try, albeit with some really loose "connections", and it didn't seem to do anything. I disconnected it and reconnected it with it powered up and saw the unsynced image change, but not to something discernible. Should the two "+-horizontal/comp sync" pins on the chassis be spliced together and connected to the single "composite sync" pin on the video board (pin 6)?
 
Pin 1 and 5 on the K7500 are connected together on the chassis according to the schematic. Instead of using wire and assuming you don't have the correct tool, remove the vertical and horizontal sync from the 720 connector. You push a tab down gently with the screwdriver on the side of the connector and it should lower the tab so you can slide the pin out of the connector. Now put the horizontal pin back into the connector, but in the composite sync spot. Double check that the pins are orientated correctly on the connector for the monitor and if not move them the same way. Then give it a try.
 
I tried a variation of that. The connector on the video board end is so small that I can't really get the pins out. What I did was connect an 18 gauge purple wire into the video board connector, just like all the other wires are connected, and tested for continuity to make sure it was fully seated. Then, on the monitor chassis end, I removed both the horizontal/comp sync wire and vert sync wire, and placed my new/purple comp sync wire into the connector at position 5 (original hor/comp sync wire). Nothing. I took the purple wire back out and connected it to position 1 and had the same result. I suppose that I might have a bad comp sync pin on the video board, but that seems pretty unlikely to me. Before trying your suggestion, I also tried removing just the vert sync pin, leaving the original horizontal connection (pin 5), and connecting the comp sync to the other horizontal connection (pin 1). That didn't do anything either. Ugh...
 
Okay. Just tried something different. I just removed the vert sync wire and comp sync and just left the horizontal in it's original position and I have a picture! The problem is, that I can't get the vertical hold to hold. I can get it steady for a few seconds, but then it starts rolling slightly. Thoughts anyone?

Edit-I messed around with it again and lost the picture. Then I saw that my vertical sync wire was hanging loosely right near a cap on the chassis and realized that it must have touched it by accident and shorted it. Well, I took the vert sync wire and touched the cap again...tiny little spark...and then I got my picture back again! I seem to remember reading about shorting one of the sync wires to get it synced, but I don't remember where. I'll have to go look that up.
 
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So here's a video of what's going on.



Comp sync (pin 6 on j19) is connected via a single wire to pin 5 (+- horizontal/comp sync) on the monitor chassis. The vert sync and horizontal sync wires are still connected to the video board, but are not connected to the chassis (I removed them from the connector). When I touch a gray resistor (specifically R823) with the vert sync wire connected to the video board, I get a small spark and the picture appears (it also happens when do it with the horizontal sync wire). This happened by accident. Also by accident, on a different occasion one of those wires touched something else on the chassis and fried something on that video board...so now I've got to figure what happened with that one. However, I have another partially working video board (glitchy graphics) that I put in and had the same result...so whatever I did, it didn't mess with the chassis. I've tried searching and reading through threads for hours, but can't figure out what that "short" does to cause it to sync, or how I come up with a permanent way to do it, as the sync is undone every time it's powered down.
 
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