Sega MC-2000S Restoration Trouble

Tecnolock

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Picked up a free Sega Turbo upright cabinet in pretty rough shape. Worked my way through the power supply boards and then moved the CRT. On initial power up, had no neck glow, so I removed the tube/chassis from the cabinet and over to the work bench. To start, I re-capped it with a cap kit from Arcaderapiarparts dot com. Then crawled through the board testing each transistor, out of board by hand, only finding a failure at Q902 (A1091). Reflowed all the connectors, flyback, and tube socket. After a final inspection for cold solder joints, broken traces, etc, I felt good enough to power it up for another test. Set the variac/isolation transformer to 100AC and powered it up.

The tube turned on nice and after adjusting the contrast there were bright retrace lines. Connected a BK 1249 NTSC (Tested working on alt screen) generator to the R,G,B,GND,SYNC inputs and was able to lock the scrolling lines but cant seem to get any image. (See image below). Adjusting the V/H positioning/Hold knobs effect the image but its always gray lines.
MC-2000S Screen Problem.JPG
Focusing in on the video amplification section of the board, Q107 controls the base leads on the video amp transistors, and seemed like a good place to start. The Transistor looked good but the wiper arms on the video bias pot (RV104) were missing and reading open.
Went back to test all the trip pots, and any of the "V8K4-1" style were bad. Ended up replacing 4x 5K trim pots used for Color gain adjust in the video amp section and 1x 3K trim pot for Power Drive in the High Voltage section. I set them to middle position and figured I could adjust from there.

On initial power up, the set was emitting a high pitch whine and had bright white bars flashing across the screen. You could almost hear an audible click each time the screen flashed. Adjusting the "Screen" knob on the flyback helped a little. Looking around online, a few folks said the B+ voltage for this monitor should be around 105v. Using the test point near fuse F902, I adjusted the (new)R910 trim pot up till the meter read 107 volts. The whine subsided and the screen settled. If I tune it any lower and the screen goes crazy again and the high pitch whine comes back. If I adjust the Video Bias to high the screen goes crazy. Adjusting the Vertical/ Horizontal knob let me fill the screen, making me think IC401 (Video Sync IC) is fine.
IMG_0281.PNG
I'm a novice at best when it comes to CRT repair and enjoying learning as I go, as such, I'm not sure if the problem I'm having is still the video input/output section or is it something in the Horizontal/Vertical section of the PCB. If anyone has any ideas or suggestion please pass them my way.
 
I'm going through the same situation with my MC-2000. Recapped, swapped known working flyback, new HOT, B+ to 105V, all three 5K pots replaced on RGB Gain, Video Bias pot replaced. I get an image, but I also get those white rescan lines with or without a video signal. Image is really washed out as well. Going to socket IC401 and drop in a new one next to rule it out. Bias adjust per manual so TP3 is ~6V on black signal level and ~10V on white signal level.

Whenever I drop the Screen quickly on the Flyback, I get a near perfect picture for a split second and then back to being washed out with the rescan lines.

Here's my thread with an image. https://forums.arcade-museum.com/threads/sega-nanao-mc-2000-s-horizontal-retrace-issue.540328/
 
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I'm going through the same situation with my MC-2000. Recapped, swapped known working flyback, new HOT, B+ to 105V, all three 5K pots replaced on RGB Gain, Video Bias pot replaced. I get an image, but I also get those white rescan lines with or without a video signal. Image is really washed out as well. Going to socket IC401 and drop in a new one next to rule it out. Bias adjust per manual so TP3 is ~6V on black signal level and ~10V on white signal level.

Whenever I drop the Screen quickly on the Flyback, I get a near perfect picture for a split second and then back to being washed out with the rescan lines.

Here's my thread with an image. https://forums.arcade-museum.com/threads/sega-nanao-mc-2000-s-horizontal-retrace-issue.540328/
Thanks for sharing your repair notes. I've popped over to the link and left a post. It's nice not being the only one out there working on a 30+ year old CRT. Just a thought, since your getting an image and its washing out, it could be an issue with the tube it's self. I've watched a few videos now with folks who have used a CRT Tube restorer to clean beam guns inside. Here's link to a pretty good example. Spy Hunter Arcade Restoration with The 8-Bit Guy (19:25 for tube stuff)
 
Thanks for sharing your repair notes. I've popped over to the link and left a post. It's nice not being the only one out there working on a 30+ year old CRT. Just a thought, since your getting an image and its washing out, it could be an issue with the tube it's self. I've watched a few videos now with folks who have used a CRT Tube restorer to clean beam guns inside. Here's link to a pretty good example. Spy Hunter Arcade Restoration with The 8-Bit Guy (19:25 for tube stuff)
I have not tried to rejuve yet. I'm not entirely sure that would clean up the rescan issue or not. Someone with more knowledge than me would have to chime in with some answers. I do have a rejuvenator, but never used it on a tube displaying issues of rescanning.

I have another known working MC-2000 that I may swap chassis on and see what I get to see if the issue follows the chassis or the tube. I will report back.
 
I have not tried to rejuve yet. I'm not entirely sure that would clean up the rescan issue or not. Someone with more knowledge than me would have to chime in with some answers. I do have a rejuvenator, but never used it on a tube displaying issues of rescanning.

I have another known working MC-2000 that I may swap chassis on and see what I get to see if the issue follows the chassis or the tube. I will report back.
My apologizes for the confusion. My rejuvenator comment was more aimed at " I get a perfect picture and then the brightness immeadiately climbs back up on it's own" and not the rescan. But ya, I'm no expert, just someone taking a stab at it.

I do have a question though. RV505 is the brightness adjustment pot (30k). Measuring RV505 in circuit gives me odd readings, from turned full left -> mid way -> full right reads 0Ω(L) -> 9.2kΩ (1/2) -> 4.42kΩ(R). Measuring it out of circuit tests okay. If you had a moment, could you possible measure the ohms on the same pot on your chassis to help narrow my issue down? Either way, thank you for reading through my post.
 
I do have a question though. RV505 is the brightness adjustment pot (30k). Measuring RV505 in circuit gives me odd readings, from turned full left -> mid way -> full right reads 0Ω(L) -> 9.2kΩ (1/2) -> 4.42kΩ(R). Measuring it out of circuit tests okay. If you had a moment, could you possible measure the ohms on the same pot on your chassis to help narrow my issue down? Either way, thank you for reading through my post.

A couple of things to report. I just went and pulled the other monitor that I thought was a MC2000 and it's a MC2030 with a different neck socket, so I didn't get anywhere with that. I also don't have a CR25 adapter to test this tube, so I'm going to have to build an adapter which may take a while to get around to.

Brightness pot readings are as follows:
In circuit ~32Ω(L) -> ~8kΩ(1/2) -> ~4.2kΩ(R).
Out of circuit ~30Ω(L) -> ~14.1kΩ(1/2) -> ~28kΩ(R).
 
A couple of things to report. I just went and pulled the other monitor that I thought was a MC2000 and it's a MC2030 with a different neck socket, so I didn't get anywhere with that. I also don't have a CR25 adapter to test this tube, so I'm going to have to build an adapter which may take a while to get around to.

Brightness pot readings are as follows:
In circuit ~32Ω(L) -> ~8kΩ(1/2) -> ~4.2kΩ(R).
Out of circuit ~30Ω(L) -> ~14.1kΩ(1/2) -> ~28kΩ(R).
Thank you for passing those measurements along, seeming similar readings was reassuring. I'm going to get my flyback reinstalled and see if cleaning the badly oxidized pins made any real difference. Next step will be socketing and swapping out IC401. Will post when I have an update.
 
~It's Alive!!!!!~
The last thing holding me back was that blasted IC401 Signal Processor. Picked up a couple new old stock HA11235 on eBay for around $12 shipped. Socketed the new chip and after tuning the hold/position/Screen adjustments, I got a nice clean image. This had to be the most in depth I've done to date and ecstatic to breath some life into it.
 

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