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Thread: Help Needed w/ Nanao MS8-26SG

  1. #1
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    Help Needed w/ Nanao MS8-26SG

    I've posted this across a couple forums, not getting much help, mucking through it with what little information I can find on this monitor. Hoping someone here is familiar with it (standard Aero City 26" monitor, but NOT the same as the more common MS8-26SU).

    I did a cap kit on the chassis. Was working before, is not working now. I have rechecked all my work about 10 times now...verified orientation, correct placement, even pulled all the old caps from the trash and re-checked what was installed against what came out.

    AC power is good where it lands at the board. Fuses are good. There's a very faint hum or buzz coming from the neck area...the standard sound of a monitor in operation, but much much more faint. No neck glow.

    Following this thread for guidance, from someone who had the same experience on 3 of 4 capped chassis: https://forums.arcade-museum.com/sho...d.php?t=295290

    I am powering the monitor with an iso tap, plugged in on the isolated side, getting around 102-103V AC through fuse F901. I've read these chassis are okay at 120V, and I was clearly running it on 120V for the few months I've had it so far, with no problems. But, nonetheless, I'm going with what's marked on the tube sticker for testing.

    Soldered a wire to the negative side of the filter cap for my ground. Getting 93.8V DC at F902. I put the isotap up one tick, to get around 108V AC, and still 93.8V DC at F902.

    Checked voltage at the IC301 vertical board and there was nothing there...at least not on pin 9, which is supposed to be VCC. I started desoldering, and unbeknownst to me, was doing it with the monitor still plugged in. :-o I got to I think the 4th or 5th pin, sucked up the solder, and instantaneously the monitor came on. Scared the crap out of me.

    I immediately unplugged and discharged, and got that beatiful POP from the discharge. I then resoldered and checked for shorts, figuring I must've had a short, and found 2 pins shorted, which are continuous via the vertical board, and 2 pins shorted that are continuous on the chassis. No other shorts that shouldn't be there. Re-powered and nothing.

    Then I looked closer, and the connection at the board that goes to pin 9 is floating. It is a through hole with no connectivity. And there's no way I'm installing the vertical board backwards. It will not physically fit if rotated 180 degrees. I also looked at a picture I had taken before starting work, and it is properly oriented.

    Also checked Q901 - 94.1VDC on the base, 93.9VDC on the emitter.

    I adjust B+ voltage up to get a solid 100V DC at F901.

    I then realized pin 9 is labeled on the board, and it seems the pins get numbered counter-clockwise, with 1 being at the top right of the notched end of the chip. Pin 9 was measuring around 10.7V DC.

    Checked voltage across the filter cap - 133.8V

    No improvement other than that single instance when I was desoldering with the board powered.

    I'm starting to dissect IC301 and ins/outs to/from it.

    Any other suggestions?
    Last edited by NoAffinity; 04-28-2017 at 09:25 AM.

  2. #2
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    I've got 3.5V DC on pin 4 of the vertical board (V VCC), and 12.6V DC on pin 12 (H VCC). Any idea if these are correct...or should they be the same?
    I also started poking around on the neckboard. I confirmed that grounds are continuous and good, from the tube through the neckboard and to the flyback. None of those, however, are continuous to the filter cap '-' side. Is that right?

    I'm also not finding any voltage at the neckboard. Is that also right?

    Lastly, 4 pins of the flyback have 3.7V DC on them.

    Not sure if any of these are useful clues...

  3. #3
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    Checked the HOT. The base and emitter have continuity. Is that right?

    http://www.datasheetspdf.com/PDF/D1880/606258/1

    93.4V DC on the collector. No voltage on the base or emitter.

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    Monitors can be a bear. I have more familiarity with the Ms9-29su to be honest, but will try to chime in here.
    If you were doing work on IC301 when the monitor came on momentarily, then IC301 is your most probably culprit. You could risk just replacing the IC, or if you have an oscilloscope, you could check out exactly what frequencies you are getting off that chip.
    If neither of those are an option, Sterling over at KLOV has been working hard on the ms8-26su, and should be able to at least give guidance despite the differences....-->https://forums.arcade-museum.com/arc.../t-332652.html
    or
    Harvey's - 11507 W Pico Blvd, Los Angeles, CA is a place thats on the Facebook CRT collective's reputable vendor list.

    Hopefully any of that helps.
    I wish you luck!

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    Thank you, Bagheera369. I have been focusing on IC301. IC301 -> <- me

    I haven't gotten much input at KLOV, but have been getting some pretty extensive help on the Arcade Otaku forums. I am about at the point that I'm ready to hand it over to somebody and *hopefully* just be done with it. Thank you for the recommendation on Harvey's.

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    Found the problem. Or, rather, grantspain at the Arcade Otaku forums did. C560 was a 47uf 250V cap in the cap kit I got. It is supposed to be a .47uf (160V minimum). It's apparently a fairly common issue, as the one schematic of the SU chassis that is floating around out there is fairly difficult to read.

    Either way, I'm back in action!




  7. #7
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    Holy cow. One wrong cap, giving you complete monitor shutdown......damn, that's rough...and on a completely different circuit no less. Now I am really curious, what part of the 500 circuit was affecting that vertical 300 circuit enough that desoldering caused you to finally get power?

    Anyhow, congratulations....and by the way, that's a BEAUTIFUL cab. Congrats!

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