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Thread: NEC XP29 - Geometry issues

  1. #1
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    NEC XP29 - Geometry issues

    Hey folks - thought I would post this here and see if anyone has any thoughts on my NEC XP29's geometry.

    I was looking for a local tech (nor cal), but not having much luck. Basically the long and short of it is , I have some warping happening at the bottom left of the screen. Adjusting trapezoid settings via OSD, never quite gets it right. I have another PVM style monitor (Sony 2950) and it's geometry is fine...

    Before I go down the path of recapping, (which I was told by a TV tech won't fix this issue although I think that's debatable), I thought I would see if you all had some suggestions?

    Here's what's happening -


    https://www.youtube.com/watch?v=9CMdePuEeB0

    and...here's a list to a post I made on Reddit earlier this year.

    https://www.reddit.com/r/crtgaming/c...g_for_capable/

    I'm probably going to try some magnet convergence strips (Which was suggested by someone,) although I'm not sure that would address this issue (it's not a convergence issue) and, then possibly recap myself, but really don't want to ruin an otherwise nice CRT. I'm famliar with arcade crts so don't mind taking a look under the hood, but it's obviously somewhat risky

    Any suggestions appreciated.

  2. #2
    a.k.a. Mother Teresa
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    CORY's Avatar
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    This kind of CRTs are usually much more complex than arcade CRTs. I just opened a 29" multisync monitor (Mitsubishi AM-something) and it's literally a jungle inside. There's much more adjustments than any arcade CRT I've ever seen. I highly recommend you do a cap kit on the power supply before you go any further. It fixed the geometry issues I had on mine.

  3. #3
    Timid Neo Newbie

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    Quote Originally Posted by CORY View Post
    This kind of CRTs are usually much more complex than arcade CRTs. I just opened a 29" multisync monitor (Mitsubishi AM-something) and it's literally a jungle inside. There's much more adjustments than any arcade CRT I've ever seen. I highly recommend you do a cap kit on the power supply before you go any further. It fixed the geometry issues I had on mine.

    Hi - thanks alot, that's a definite starting point. I have seen alot of the Mitsubishi's since I got into this hobby, I think they are supposedly very similar to the XM29. Although mine is an XP29 (supports higher resolutions/refresh rates, etc), someone else commented on my video have a similar geometry issue....anyway someone told me there weren't too many capacitors on this unit (although there are 3 boards) but I haven't looked yet.

    When I start to attempt, I was going to look at the deflection board, as that was where I was told trapezoid control is likely on - I'm assuming the deflection board is different than the power supply? (possibly dumb question))

    Do you have a suggestion on best approach to source and identify caps for such a behemoth? ? I read somewhere folks mentioning that you don't want to just straight recap, and you need to note potentiameter settings, but I'm not too sure if that applies here.. Thanks again!!
    Last edited by brandonx76; 08-28-2017 at 07:42 PM.

  4. #4
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    The first thing I'd do (apart from getting the service manual and properly discharging the tube and filter caps) is visually inspect the caps, check for any bulging ones or any leaks. The next step would be to check for cold joints under a good light and maybe even a magnifier if you have one. After that is where it gets a little complicated, you can use a multimeter to check for dead/open caps but bad caps would still read as good, and even with an ESR meter you can't tell if a cap is drying up until you take it out of the circuit. Doing a recap is most likely your best bet since it involves the least amount of highly technical work like getting a scope and isolation transformer to track live voltages through the set to find where it's being screwed up.

    Noting the potentiometer settings is a good idea but doesn't always help, your best way to handle that is to check the service manual for what each pot should be set to. It'll tell you where there's a test point on the chassis to clip your meter onto, and really the only pot you have to be exact with is the B+ voltage, which is something you need to be prepared to safely check after changing the power section caps.
    -Andreas

  5. #5
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    Thanks for suggestions SnappleMan -

    Based on what I'm reading, I would like to make sure I address the Deflection board...probably do a full recap there. I'm assuming I have to disassemble the entire tv to get to it but not sure...anyone worked on deflection board?

    Then, rookie question, I'm assuming I can look at each cap and get a replacement for it. Any suggestions for where to source them from and what spec/type to use?

  6. #6
    Member SnappleMan's Avatar
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    You don't necessarily have to disassemble the tv but it helps a lot to have the boards out onto a workable surface. I'm still an amateur at this, but looking at your problem I'd say you should find the horizontal output section first and focus there. The horizontal output transistor is usually the biggest one and is mounted to a heat sink, if you change the caps there it might just improve the picture, but I wouldn't expect perfect geometry out of a CRT ever.

    I can't tell from the video but is the tv flat screen or rounded? If it's flat you will always have to deal with at least some minor warping of the image as it passes the center.

    As far as buying capacitors I usually get the Nichicon ones on Amazon or Ebay, ones that come in assorted boxes. They cost more but it's just easier for me, I'm sure there's a better way to get them for the more experienced people. I get a couple boxes that have different ranges of values, you'll need to cover a wide range from like 0.01uf-1000uf at 50-100v, and a few high voltage caps that are rated for 250v+. Look at the manual and check the board for the capacitors around the horizontal output section, there's usually a 22uf/200v one there somewhere.

    If you plan on tackling the power section you'll want to look at getting a new filter capacitor, that's usually around 450uf/200v+.
    Last edited by SnappleMan; 08-29-2017 at 10:16 PM.
    -Andreas

  7. #7
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    I've been having the same geometry issue with my Pvm 20l5 and 2530.

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