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Nanao MS8-26SG - can't get focus before and after recap/flyback

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gasgesgos

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Hi all, I'm running a MS8-26SG (from one of my Aeros) and can't seem to get the focus dialed in fully. It's been an issue on this one since I got it. I've recapped it (figured it was a long shot, and I'd get fresh ones on while I had it out) and just installed a new flyback. I adjust the focus all to one direction, and it's just not far enough. It feels like I need that focus knob to turn just a little bit more :)

At the lowest practical setting for brightness and the focus knob complete turned to one direction, it's not quite enough. The focus improves after turning the brightness down to "barely visible", but I noticed there's still a lot of room for brightness adjustment way below the threshold of what is visible. Even with the brightness down, the focus can't quite get to a good level.

The colors themselves look good, they can be vibrant, and it looks like it'll be great once it's in focus. B+ is at 93.3v, read from F902, which I've read is expected for that chassis. Are there some other areas I should test out or components to swap/verify? Would a rejuvenator maybe get things back to a level to where the focus knob would be able to adjusted to a good spot?

Any help or ideas of things to test would be much appreciated, thanks!
 
Could be a tube issue. Borrow a rejuvenator and see what kind of readings you get.

Out of interest, where did the flyback come from?
 
Derick2k said:
Does the focus adjustment also affect brightness?
Click to expand...
It doesn't change the brightness, no.

nem said:
Could be a tube issue. Borrow a rejuvenator and see what kind of readings you get.

Out of interest, where did the flyback come from?
Click to expand...
I got it from https://www.arcadepartsandrepair.com/. It's listed as being for a MS8-26SU, but the part number exactly matches what came off of my 26SG.

I'll have to see about finding a rejuvenator and see what I get from that. I don't know if anyone local has one, so I might end up having to add to my tool collection :)
 
Derick2k said:
Does the focus adjustment also affect brightness?
Click to expand...
One correction: tonight while working on it, I noticed the focus knob was also adjusting the brightness a little bit.

I ended up testing some resistors, and found a rather large 5.6k one on the chassis that was calculating out to be at 5.1k, so there's something else to follow up on too, though I'm not sure if that's going to brightness/focus though, I can't find solid schematics on the 26sg :(
 
I had a a very close issue, basically my unit going in focus very slowly, replaced the crt socket, checked the B+, all caps, the issue remain then casually replaced the step down tranformer with one bigger and with more Amperage rate, (5A) it worked perfectly with no issue
 
An analyzer would be good to test the CRT. A HV probe would be good to test the focus pin V and get an actual measurements on it.
 
When the focus drift in and out its the flyback but if the focus is never good could be oxyde inside the crt socket wich need to be replaced if even this not help then it's the tube :(
 
Agree some test are needed with analyzer/hv probe to take measurements. A leaky or oxidized socket could be the issue, you could try cleaning the socket pins.
 
The focus is still drifting, however much more slowly with the updated flyback and some resoldering and cleaning. On a fully cold startup, it starts with the focus knob in a very acceptable place, then drifts away over the course of 30 minutes to stabilize focus at a point slightly outside of the knobs range. For comparison, the other flyback started at the edge of the focus range and moved out of range after 5 minutes, eventually turning into an unviewable blob of an image.

From what I read, these ones don't necessarily go bad often, so the odds that I'd have a bad one, order a new one, then have that one also be bad in the same way have to be slim.

Cleaning the pins sounds promising, I did find that the neck socket did have a wonky connection for one of the pins. What's recommended for cleaning the pins and sockets? Deoxit and the world's tiniest scrub brush? WD-40?

I'll have to get some equipment for testing HV and the tube. Hopefully a quick cleaning does the trick.

Thanks a ton for the advice and help on this!
 
Sounds like possibly a component is changing value as it warms up, could be a resistor or capacitor. If you get a can of freeze spray you can test components tied to the focus voltage circuit. Let the tube warm up to where it drifts out of the focus range of the knob, then chill a component at a time until you notice a focus change. These could be at the neckboard, have you recapped the neckboard as well? Test the resistors there as well. If you get a HV tester, you can see if the Focus voltage changes as the tube/chassis warms up. So possibly component value drifting changing the focus voltage, flyback issue (but you already replaced it), crt is worn (test and possibly rejuv).

Also, with the freeze spray, you should be able to also visualized bad/cracked solder joints better
 
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I started testing a few of the larger resistors, good so far, but I haven't gone through the lifted/tested all the smaller resistors yet. I didn't get to re-cap the neckboard, so I'll see what needs to be done for that one. I didn't see many caps up there, so it shouldn't be too rough.

I didn't think about freezing components, another fun thing to learn! I'll have to collect some parts and supplies this weekend to give these different techniques a try. I'll report back with my findings :)
 
There's only one cap on the neck board. It can affect brightness, not sure about focus. It's a 10uF 160V IIRC.
 
nem said:
There's only one cap on the neck board. It can affect brightness, not sure about focus. It's a 10uF 160V IIRC.
Click to expand...
Ahh yeah, I see the one. I was mistaken (thinking about a different neckboard), that one was replaced recently.
 
Are there any good/readable schematics for this or a similar chassis?
 
I can find some info on the 26SU, which seems to be pretty close:

The only significant difference I've noted so far is that the 26SG does not have a "Sharpness Switch" as the SU does. Such a switch would be handy right about now :)
 
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