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Screen jittering after H-Width adjustment.


Rowr

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Hi guys, i recently picked up a LAI Fatboy.

 

I've rotated the screen from vertical to horizontal without issue, though after finding the edges of the screen not extending far enough out by a few inches either side some resources online led me to believe adjusting the Horizontal width pot might help.

 

I bought the correct plastic tooling and carefully tried to adjust a few turns back or forth. At the time it appeared to not make much difference so I turned it a few rotations back to get it about where i found it and then the screen sort of went from stable to all over the place horizontally. It also developed a bit of a horizontal jitter.

 

I've spent a few hours total now adjusting the various horizontal pots to try and get the screen back, and while I can adjust it to be more or less stable the jitter is persistent and the screen is now about a third too far to the left and will rarely hold horizontally for too long.

 

I've taken out the core and examined it and it doesn't appear broken at all, I've peeked inside the pot and can't see anything obviously wrong. There is a half circle flat piece of plastic that i assume is in there to hold the thread a bit tighter?

 

I'm clutching at straws a bit over what is at fault as this is my first machine and I'm struggling to find much online regarding similar issues. The way the screen went from being stable at first to going jittery makes me think perhaps a loose solder joint or something nearby when I adjusted it has gone off or something. I've checked for loose wires.

 

So i'm aware now that there is a jumper I would of been better of trying first to resolve the screen width issue and that I was always going to get minimal adjustment from the H size pot. So yeh feeling pretty deflated that I touched it at all now.

 

A few other things prior to this though things were still working ok, is that upon powering up the screen starts blurry and will gradually focus in over 15 minutes (although this might be temperature related as today being a warmer day it was clear from the outset when i powered it on. Also the vertical position pot snapped off when i first went to adjust it, it seems the legs on it were already a bit weakened although in hindsight I should of been a bit gentler.

 

Now i've contacted Jomac and plan to drop the chassis in as most threads I found regarding similar issues end with that conclusion and i'm too far over my head to be able to diagnose what is going on. But I was hoping if anyone has some more familiarity with what it could be that might make it a bit easier for me to either attempt to fix it instead of sending it off or at least narrow it down for when I send it in.

 

I believe the chassis is a nanao ms8 (26a?)

 

Sorry for a bit of a depressing first post, thanks for reading.

 

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Well, it's possible you might be able to track down the fault causing the jitter. That's likely to be in the horizontal deflection area. But the focus issue means the resin around the flyback's core is cracking as it ages, i believe. In some cases this can be a fire risk. Taking 15 mins to come into focus means it's time to replace it. Keep in mind that Joey won't work on chassis if you've worked on it yourself though.

 

Welcome to AA, by the way :)

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Thank you very much that gives me something to go on and thanks for the welcome :)

 

Hmm the flyback situation doesn't sound great...

 

I guess I'll get the chassis out and take a look around those areas, though I'll likely leave it to Joey.

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Well got the chassis off, i'm not clever enough to know if there is anything obvious here but here are some pics in case someone can see something.

 

I mean it looks like someone has done something here with this h width coil with the rubber sleeve at the back of the board but its hard to see if things are as they should be. My guess is some part of the solder has cracked where its supposed bridge across or something.

 

The flyback core hardly looks like it's falling apart or anything compared to what I have seen online with people having it arcing etc so I'm not sure what that's all about. Is that where I am looking in regards to the resin? my assumption is that your referring to within the hard casing.

 

Any other reasons you can think of in regard to the focus thing? Just a bit odd to me it's sort of gone from being fine one minute to taking a while instead of a gradual worsening. Also the link with warmer weather and the fact it turned on focused out of the gate before.

 

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Edited by Rowr
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I may not have been very clear. The flyback will have been sealed/potted into its case when it was made. Assuming I'm even right to begin with, and it's damaged or just aging, effectively, the damage could even be inside some of the coils. And it's probably the accumulation of hundreds tiny flaws. You can't get in there, it can't be fixed. It's amazing how often old electronics will go from seeming fine to completely broken as something that must have been aging for years finally gives up. If the problem isn't with the flyback, it might be inside the tube. And that's even more impossible to get into.

 

Photos aren't going to be much good for diagnosing the horizontal offset problem either, sadly. A failed or out-of-spec component can't be spotted unless there's physical damage, and a dry joint or crack is going to be difficult as well. You could start by examining each solder joint, and metering for connectivity from place to place. You could also try running the chassis (you need the tube connected, obviously) and perhaps pushing gently to flex the board with a piece of dowell or something else non-conductive. After that. you might need to start desoldering components and testing them, starting in the horizontal section - remembering that Joey won't touch the chassis after you start this step.

 

The horizontal deflection circuits are intimately linked to the flyback in any raster CRT, so for all i actually know the whole problem might be related to the flyback. Or a capacitor in the horizontal section. Or something else entirely. Deflection problems are not a great place to start when it comes to learning CRT repair.

 

If you do find a fix, or if you send the chassis to Joey, i'd be keen to learn what the problem actually was :)

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Ok thanks for the specifics that helps me understand a lot better.

 

I think it's off to Joey for sure, as it's probably a bit beyond me in complexity and honestly it looks finicky as hell. I haven't looked at the back of one of these chassis before, but if I had to guess it looks like that H width coil was replaced perhaps and me putting a little tension on it has upset some of the delicate solder work. I mean I really don't know for sure but given it went from fine to screwy in the act of playing with it that seems most likely.

 

I'd rather have it in working condition if possible rather than donate it too science in the act of poking around too much :)

 

Otherwise I'm stuck here justifying the cost of an old wooden box to my wife :D

 

I guess as far as the flyback and the focus warm up issue I will have to see how that goes, I can live with it in it's current state. If it gets worse I guess my option would be to look at a replacement and the costs associated.

In any case it's kind of secondary to having the horizontal positioning issue resolved so i'll wait on that.

 

I've got a Sony trinitron flatscreen crt sitting in my shed that I found kerbside a few weeks ago that looks like it will fit the cabinet perfectly when decased. Though my preference is to try and salvage the original stuff if possible. Especially as it was basically working fine until I turned the wrong knob.

 

Well I'll drop the chassis in next week and fingers crossed I guess, otherwise I'll be back here asking questions about pulling a trinitron apart :)

Edited by Rowr
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A late update in case it helps others down the line.

Sent it in to jomac and it was an issue with the sync module. Apparently these chassis have a low tolerance for multi carts putting them out of range. Probably not helped by me dicking around with all the adjustments.

 

I changed the width jumper and that resolved the screen reaching to full horizontal width.

 

I also found my cut offs at what seemed like neutral seemed to be too high, resulting on me needing the flyback and brightness higher than probably preferable. After dialing that stuff back I'm not getting unfocused picture after first turning it on.

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Of course now i'm trying to diagnose an issue of the screen being horizontally too wide since changing the jumper over <_>

 

Well perhaps...The test pattern on my game board seems to show as too wide as i'm not getting the last box completed either side as shown in the photo below, I can adjust the image to the right with the H phase and H hold so that the last line completes on the left hand side, but then my picture on the game is half an inch in on that side. Also you will notice that there is an extra red line there as if the picture is folding in.

 

For reference, I checked the same game board in Mame on my lcd tv and it shows the boxes as completing.

 

I wouldn't mind even if the picture was cut off either side or something but really what I am trying to eliminate are these white vertical lines pictured below, they are most obvious when the screen is white or grey.

 

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Trying to google this issue I get a whole range of possible culprits, from capacitors to convergence to screen burn in...If anyone can identify from the pictures where I should go with this any help is appreciated.

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Firstly forgot about what you see in MAME , that has nothing at all to do with genuine arcade neither do LCD monitors , very few game test patterns can be aligned perfectly on 30 year old arcade monitors , using an non genuine arcade source as in MAME and an LCD that didn't even exist when these games were made is always going to leave you disappointed.

 

The lines you are seeing is not a chassis fault , it is ground fault usually caused by people earthing those chassis or the monitor metal frame which should always be totally isolated from earth / mains earth.

Monitor chassis can't produce images of lines or anything at all that is not being input to them , so in your case the monitor is displaying interference that is be induced by something wiring related .

Those google results are not even close to being correct.

 

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.

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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.
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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! :D 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 - - -

 

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.

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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.

 

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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...

 

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Edited by Rowr
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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.

Edited by Rowr
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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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