Sega Nanao MC-2000-S Horizontal Retrace Issue

Radford119

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Donor 2011, 2023
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Recently recapped a Nanao MC-2000-S and I was wondering if anyone has ever experienced this issue. No matter what I do I cannot adjust these horizontal retrace lines out. The image below is with the Screen and Brightness turned all the way down. However, if I have the SCREEN adjusted maybe mid way and I quickly turn it all the way down, I get a perfect picture and then the brightness immeadiately climbs back up on it's own. Did this on both flybacks.

So far I've done the following:
Cap Kit
New Filter Cap
New HOT
B+ is 104V
Swapped flybacks with a known working one, same issue.
Reflowed the entire chassis and neck.
No cracks on the chassis.
Issue was present before the cap kit was installed.
New brightness pot installed.

Any help or insight on this would be greatly appreciated.

Thanks,
Radford119
 

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Solder bridge somewhere
I just went and double checked with a magnifying glass on the bottom of chassis and neck, found nothing. I'm going to do the top side next.

Update: Topside checked, nothing.
 
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Thank for dropping a comment in my thread. Talking with folks from the arcade sub reddit, they say the horizontal retrace lines usually appear when the gain is set too high on the flyback. Doesn't sound relevant in your case since the issue persisted even after installing a replacement flyback. Here is a link to the service manual MC-2000-S Manual. Section 7 - pg17 has some screen voltage adjustments, says to measure between G2 & E2 on the neckboard, should be 210V.

I've been attempting to restore a MC-2000-S out of a Sege Turbo and as you seen in my thread, I've have hit a wall. My voltage between G2&E2 is at 148v and adjusting the RV503 (Brightness) pot does not change the voltage. This is the only lead I currently have to go on for mine and I'm stumped. I've pulled and tested every transistor on the board, checked all the diodes in the relevant area, nothing. The flyback leads look a little questionable even after reflow, so I pulled it to give them a good cleaning and try to map out the coil. Since I get no image at all, IC401 seems like the next thing to rule out. This is only my second CRT and I know just enough electronic trouble shooting to get myself in trouble, but it's fun learning in the process.

Here are a couple other resources I've collected over the last couple months. Sega/Nanao Model MC-2000-S Repair Guide , Nanao MS-200S Functional Block Diagram , arcadecontrols.com forum post- 19" Nanao MC-2000-S diagnosis
 
Updates from last post.

Voltage across G2 and E2 is ~210V, right on target with what the manual states it should be. This is with the SCREEN turned all the way down on the fly.

I swapped the following with known working parts, No change:
IC401
Q402
Q401
Q502
Q504
Q505

Replaced every pot, just to rule out any weirdness, No change:

I tested every passive componet out of circuit in the video section. Nothing out of spec.

Shorted each tranistor on the neckboard with the monitor on to see what I was getting with each color. Everytime I shorted them, I got just a really weak flood of color. Never anything vibrant. Just very dull and muted.

Honestly don't know what's left. Could a bad tube cause these types of rescanning white lines? Thanks in advance for any and all help.
 
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