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Thread: Screen jittering after H-Width adjustment.

  1. #11
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    Thanks for the reply mate, I'll work through those suggestions tonight I guess I was down the wrong rabbit hole with the screen width thing, it just made sense to me in that the extra line tracks back as I move the picture to the right and completes the box, it seemed to me as though the picture was folding over to create the lines somehow I guess.

    I checked the game in MAME again and noted with my finger and it looks like the test pattern does extend further out than the game border, so seems like you are right and my width is probably correct as is. Don't worry if I was happy with an LCD and MAME I wouldn't be here trying to fix this! I just have it as a reference because my genuine pcb is japanese and I had no idea what the test menu's said without loading the english version on my PC.

    If google fails me again I'll be back I guess to work out some finer points, the transofrmer at the bottom of the cab is old and scary and I need to do some research before I poke around in general.

    - - - Updated - - -

    Quote Originally Posted by buttersoft View Post
    Can't believe i missed the fact it was an MS8, Joey has posted about the sync issues on those before. They have a very narrow range they're happy with, so you might want to make sure that whatever source you're using is at exactly that range. For something like GroovyMAME that's going to be a bummer because it will limit what you can do.
    Yes I took Joeys advice after the fix and ordered a genuine pcb. It's was a bit of a bugger as I guess i'd planned to go the groovymame route initially, but after seeing what's involved with the jpacs etc that i'd be better off just building a dedicated MAME cab from scratch with an old PC and the aforementioned trinitron at some point and keep this old girl genuine and original.

    I think i'll look at my options as far as the neogeo motherboards go though, because carts seem to be much cheaper than classic jamma games and the old neogeo exclusive fighting games are my cup of tea anyway.

  2. #12
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    Quote Originally Posted by Jomac View Post
    First thing I would do is a continuity test between mains earth and the mounting frame of the tube and of course make sure there is no earth wires connected to the chassis metal parts.
    If all clear trying joining the chassis Gnd input wire and the power supply Gnd wires on the Jamma harness.
    Check the power supply and see if the Mains Earth and Gnd is linked together with a link wire , if not try doing this , if it is connected already try removing this link.
    Make sure the stepdown transformer metal body is earthed.
    Make sure all earth connections in the cabinet are separate wires running from the same point where the earth enters the cabinet , earth points should never be daisy chained to the next point , it causes an earth loop that induces interference.
    I guess i'm somewhat out of my depth here, but reading up a bunch i'm getting somewhat of a picture of what is supposed to be here. I'm still a bit confused by terminology being used though.

    For the continuity test i'm not confident enough where i should be testing from 'mains earth'. Much of my wiring is run into and then out of a distribution box so i'm unsure if I need to be in there for this. I checked the metal frame around the monitor visually and didn't find anything it could be contacting.

    There is an earth wire connected to the chassis which connects where it powers from the transformer as pictured below but it sure seems like it's there on purpose so I thought I would post in case i'm way on the wrong track before touching it.

    I linked the chassis gnd (14 parts side) with the power supply gnd (1) at the connector of the Jamma harness, no change.

    I checked the power supply, unless i'm on the wrong track my assumption is FG is mains earth? (which answers my first question?) and there is a wire linking back from gnd. Wanted confirmation before removing this.

    The stepdown transformer metal body does not appear to be earthed to.

    Things that are earthed (like the coin doors) seem to run back to the distribution box and aren't clearly individually running back to any point. Is there a typical point where these wires usually run to? You say around where the power enters the cabinet? Or could this all be hidden in the distribution box. The distribution box itself has a conspicuous bolt on it that looks as though it's supposed to be earthed.

    Sorry if I'm way out on all of this, i'm doing my best to educate myself, without experience looking at these it's easier for me to identify things that seem out of place over things that maybe should be present that aren't. I'll do some more reading online and take another look at this tomorrow.

    DSC_0096.jpgDSC_0101.jpgDSC_0099.jpgDSC_0103.jpg

    Had another look this morning, pulled the DC power apart to check inside since the led wasn't lining up anyway so I wanted to see what was up with that. There is an earth on the back of the distribution box actually. Took some more pics.

    My understanding of how this all goes together is increasing, but i'm still unsure maybe the earth wires aren't running optimally from individual wires picking up in the one spot and that is what is potentially causing issue?

    When i put it back together and turned it on my focus issue returned and the screen went from looking like it was underwater to clear again over 10 minutes. It was colder weather overnight and I'm usually turning it on in the evenings so maybe there is something going on temperature wise I don't know...

    DSC_0106.jpgDSC_0107.jpgDSC_0113.jpgDSC_0114.jpg
    Last edited by Rowr; 2nd April 2019 at 11:24 AM.

  3. #13
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    Might be easier if you call into the workshop after work or give me a call and I,ll give you a run through what to check etc.

  4. #14
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    Well had a chat with Joey and confirmed some suspicions.

    Removed the earth from the chassis and it seems as though the interference is lessened, though still there - bit harder to see with the natural light of day and focus issues abound, i'm sure it's related to the humidity, but cleaning the flyback and reseating the neckboard didn't seem to help, will worry about that one later I guess.

    I checked and found I still have continuity on the monitor frame through the video ground wire coming back to the distribution board. I flipped it over and found that an extra video ground is running out the underside molex back to my service switch??? There's a bunch of malarky going on around the volume test and service switch and that connection that I don't understand just yet.

    Anyway I guess i'll disconnect that later tonight and see if that's the culprit.
    Edit - I guess I realised after that it's just tied into the other grounds at that point which is apparently normal I guess, so yeh not quite sure would all be a lot simpler if everything wasn't earthing off the distribution box itself. The interference is almost unnoticeable now unless you are looking for it now so I might just leave well enough alone until it drives me crazy at a later date.

    It's odd to me that so many threads i've found seem to actively suggest grounding the chassis and monitor, I can only assume this is something that varies between models or something or is dependant on how your wiring links up at the power.

    Aside from still being confused at least I feel I've learnt a bit. Thanks for the help guys.
    Last edited by Rowr; 3rd April 2019 at 09:54 PM.

  5. #15
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    Monitor chassis grounding / earthing can be a complex thing to understand but it's worth remembering that any quality 110v chassis require a isolation transformer, even in the US these means a transformer that isolates mains 110v from monitor supply 110v .
    Free voltage chassis like many that I have supplied have a built in isolation transformer in the power supply section to achieve the same thing whether running on mains 110v or 240v.

    All Nanao chassis and quality Japanese built chassis not only have the power supply section isolated from mains but the secondary flyback / high voltage section is isolated from the power supply secondary section meaning there is no physical connection between Supply Gnd and Flyback Gnd/Shield.

    The interference we get here in Australia is because ours mains operates on what's known as the MEN system which means our Neutral and Earth are tied together at all times , if you measure between Neutral and Earth on any power point you should always read 0 ohms or dead short.
    This is always an important consideration where monitors are concerned , remember we are using an Isolation transformer so there is no physical connection to the mains , but then if you connect an earth wire ( which remember is connected directly to 240v mains Neutral ) we no longer have any isolation , we have monitor chassis running on 60hz AC 110v , and introducing 50hz AC 240v into what is supposed to be a clean Gnd shield. , the results vary greatly from machine to machine but visible interference is the most common, especially if there is no mains filter on the input of the cabinet. ( always included in all LAI built machines inside the distribution box ) .

    There are plenty of other chassis designs that have all Gnd's joined together, meaning chassis power supply Gnd and secondary sections are joined which also means the video input Gnd shares the same Gnd , this can induce interference in a lot of situations and earthing the monitor metal frame is the only way to get rid of the interference , quite often just joining Gnd and FG ( Field Gnd ) on the power supply is enough to fix the issue.


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