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Nanao MS8-26U


Christy

Question

So I had partial vertical collapse and therefore replaced R433 and C433. But I used a 25v 10uf instead of the 50v 10uf I read online, because 25v 10uf is what was in there already. And I used a 2.2k 1/2w (0.5w) resistor instead of a 1/4w or 1/8w resistor, because that’s all I had. It fixed the collapse, sort of. Now I have this image. Kind of stretched/scaled top quarter of the screen and badly bowed sides. And the colour are cock-eyed obviously, but not started in them yet. Any ideas what to look at?

 

IMG_1892.JPG

 

IMG_1891.JPG

 

IMG_1893.JPG

 

 

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Edited by Christy
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With capacitors you can always go up in voltage but never down but the uF must remain the same.

 

Yeah, that’s what I stayed with. Cheers. I’ve not done a full cap replacement yet. Just trying to learn the causes of things before going all shotgun on it. If that’ll fix it in any case?. I have a feeling it’s not the right size monitor tbh. As the tube does not fit into the original monitor brackets. It’s s little bigger. Not sure where to go with it tbh.

 

 

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To be honest it looks like your yoke might be about to die, the caps may have been bad as well and may even make it a little better when replaced.

I would also add that while capacitors are often an issue there are many other consideration on old chassis and yokes that can die as well and are just as common sometimes repairing one thing will aggravate the others and the unit dies again.

Higher wattage resistors wont affect anything when replaced unless they are out of spec as well but I doubt it would be what is in your pictures, the cap while 25volts should not replace a 50volt may still be OK as not all designs use the 50volts unless the schematics say so. generally however if it really was around 40~50volts where it was mounted a 25volt cap would die pretty quick and probably even pop its top.

if you dont have the right capacitor you can bodge one by roughly remembering this rule. In series two of the same value capacitor will double voltage rating but halve capacitance. So for 50volt 10uf you could use 2x 25volt 20uf or close being 22uf in series (not parallel!) .

it would at least help see if you have other issues with the chassis or yoke before buying the correct rating components.

 

My bets on the yoke....

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Nanao MS8-26U

 

To be honest it looks like your yoke might be about to die, the caps may have been bad as well and may even make it a little better when replaced.

I would also add that while capacitors are often an issue there are many other consideration on old chassis and yokes that can die as well and are just as common sometimes repairing one thing will aggravate the others and the unit dies again.

Higher wattage resistors wont affect anything when replaced unless they are out of spec as well but I doubt it would be what is in your pictures, the cap while 25volts should not replace a 50volt may still be OK as not all designs use the 50volts unless the schematics say so. generally however if it really was around 40~50volts where it was mounted a 25volt cap would die pretty quick and probably even pop its top.

if you dont have the right capacitor you can bodge one by roughly remembering this rule. In series two of the same value capacitor will double voltage rating but halve capacitance. So for 50volt 10uf you could use 2x 25volt 20uf or close being 22uf in series (not parallel!) .

it would at least help see if you have other issues with the chassis or yoke before buying the correct rating components.

 

My bets on the yoke....

 

Thanks for the advice. What. Can be done to remedy a yolk? Interesting observation on the yolk though, because it was originally damaged to some degree. Not the yolk per se, but the magnetic rings and their plastic surround were cracked. The plastic surround also had a very fine/thin coil within it. So I have used a spare plastic surround and rings from another, smaller monitor, which has no coil. It did stabilise the simmering out of the picture though. And it still allows the colours to be altered. But if it is the yolk, could it be there in lies the issue; with the deflection rings and surround? Perhaps I can solder some copper thread and glue the old thin coil back together? Will look at it closely. No idea at all as to what those pins that extrude from it are for and if they connect to anywhere though.

 

IMG_5804.JPG

 

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IMG_5805.JPG

 

 

 

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Nanao MS8-26U

 

So I made some adjustments and have it looking like this. If I expand the screen upwards then it breaks up like above. It won’t extend to fill the screen vertically or horizontally. And the curved edges are still there. The deflection rings are working though, even thought they are borrowed from a smaller monitor.

 

IMG_1904.JPG

 

IMG_1903.JPG

 

 

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Edited by Christy
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Those rings are convergence rings, used to line up the three colors. The yoke is the copper winding further along and is responsible for deflection of the beam.

Broken rings or badly out of wack rings can also cause a really bad image similar to yoke failure.

At this stage I would explore the components on the chassis and ensure the right values are being used and you test and/or replace as needed. Watch out for bipolar capacitors as replacing those with polarized ones can cause all sorts of issues probably has one on there. Check also all adjustments actually work, any that don't usually have a bad capacitor behind them or a pot that's open or bad solder joints. Issues relating to bad linearity or fold over like in the first image are usually just the caps.

You can also contact JOMAC for repair if it gets to much as well, he will have the right parts to...

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Update: I did a complete capacitor replacement, regardless of if they were faulty or not. The issue is still there though; small screen and curved edges, with rolling screen if I dial the vertical size up. The colours have improved massively and really pop now though, which makes it worth it nevertheless. I’m going to try and repair, and rewind the coil on the old convergence ring bracket tomorrow and see if that makes a difference. It seems a logical repair to try. Not sure if the new rings will fit but I’ll have to see. I’ve epoxied the two pieces together tonight and will see how it goes. My thinking is that coils generate magnetic fields, etc, so makes sense to me that it could effect the yolks/convergence performance somewhat. What do you think? Need advice on the pins coming out of it too. Does anyone know if they connect to anywhere or not? TIA

 

 

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You are wasting your time playing with the convergence rings , that is the wrong CRT and Yoke for that chassis , it will be never be right it's a total mismatch and why the geometry and size are wrong.
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You are wasting your time playing with the convergence rings , that is the wrong CRT and Yoke for that chassis , it will be never be right it's a total mismatch and why the geometry and size are wrong.

 

Thank you so much Jomac.

 

Do you think the yolk has been changed on the tube, or that both yolk/CTR are just wrong?

 

The chassis name suggests a 26" tube and the one I have is about 29", I think. I initially thought the yolk was from the same 29" tube, but that the tube had been changed (being a different size). I thought this because there was a white gauze tape holding the ring-cover in place, which I looked untouched; but I have no experience here of course. I then thought that the screen being larger was an issue, but I was told that the tube size (being between 26 to 29) would not have made a major difference to the chassis/picture. Is this what you find in your experience? I checked the expected voltages for the B+, taking advise to look at there. The manual states the unloaded voltage should be 92v +/- 0.52v. My reading from the TP2 (fuse) to TP1 (Ground) was reading 60v; way off. So I was trying to weigh up what to check next, being so far I didn't think it wise to adjust the B+ pot, but happy to take advice on this too. From what your saying, do you think the load from the yolk is dragging the value down? is that right?

 

Do you know of, or can you suggest any modifications that can be made to the chassis or yolk, that could allow the tube/chassis to be saved? Is this even possible? It's playable as it is, but it looks bad, you know.

 

TIA and Thanks for your reply.

 

~TC

 

EDIT: After further investigation, I believe that the B+ voltage adjustment pot (resistor R910) is faulty, and looking to replace it. On adjustment, the voltages do not respond well, and jump around, in a range between 60 (the norm) to at most 87v. But the best I could hold it at was 77v. The good news is, that the screen size has indeed increased by doing this. So I will replace the pot and dial it to 92v, and hope this resolved the issue. I will, of course update you on the results. However, there is no value to the pot, so I am unsure at this moment what part to order. Can anyone advise me on this? TIA

Edited by Christy
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The MS8-26 is made for one tube and yoke only , the tube is a 63cm 26" Mitsubishi with a specific yoke for that chassis only.

From your pictures I can't even ID that tube / yoke combination you have I just know it's nothing like the proper one and your picture clearly shows that.

 

The B+ pot if it's adjusting at all then it will be ok , the problem is the way you are measuring it , the metal frame on these is isolated from Gnd , you have to use the rectifier Negative as the Gnd reference when testing the B+ ., at 60v or 77v you won't even get a picture.

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Thank you Jomac. You were right about the testing points. I found the correct testing locations and found the values to be a little high. Adjusted the B+ to 92v, but it was super flakey getting it there. The values were not adjusting chronologically, and were jumping about a little erratically. But, suffice to say it is now at 92v, as per the manual. The picture is naturally still messed up, and something I will research more in depth, as I continue to learn.

 

With sheer luck, I picked up another 26" MS8-26 tube and chassis today; in great working order. I tested all the voltages and all were within tolerances, except the B+ which was 2v too high. It adjusted down perfectly though. What's weird though, I attached it to the same game (Super Chase:Criminal Termination) and its still it hard to get the game to fill the screen on the vertical axis. Although, this monitor is at least square. The width was initially too wide, but it has an adjustment cable to remedy this. However, the vertical height just does not fill the screen, no matter how much I adjust the pots. I'll test it with another game asap, just to qualify this is a monitor issue. But any thoughts or ideas, very much appreciated.

 

Cheers guys.

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