Adjust Horizontal synch on my Astro

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chubsta
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Adjust Horizontal synch on my Astro

Post by chubsta » October 26th, 2008, 9:43 am

Im using an Astro City for Mame - when it first boots up there is distortion in the top part of the screen as if the horizontal synch is 'just out'. As the machine goes further into the boot and gets to a windows desktop the screen isnt as sharp as i think it should be and thee is a kind of 'shimmering' over the top of everything. As i have seen similar things befor that were due to the H-synch being ever so slightly out i would like to adjust it... this is where the problems start... i cant find the button to do it! t as got a remote board under the CP which allows most adjustments, but no synch, here are some photos of the inside of the machine from the back which show as much of the chassis as i can....

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Re: Adjust Horizontal synch on my Astro

Post by Mr-Megalo » October 26th, 2008, 9:49 am

H Sync pots are on the chassis, theres one for 24k and one for 15k
IIRC they have white resin on the pots to stop them from being changed

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 26th, 2008, 10:32 am

Mr-Megalo wrote:H Sync pots are on the chassis, theres one for 24k and one for 15k
IIRC they have white resin on the pots to stop them from being changed

soooo - should i try to change them you reckon? (the 15k one anyway as i dont use the 24k side of it...)

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 26th, 2008, 11:35 am

well, i messed with the pots and at least didnt cause any damage, although the shimmering is still there!

any ideas what to try next?

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Re: Adjust Horizontal synch on my Astro

Post by ckong » October 26th, 2008, 1:18 pm

I don't know what shimmering is, but in your first pic you see two black knobs (just below the hanging light grey cable). the top one is for focus, the bottom one for screen adjustment. If your monitor is out of focus, just turn the top one (or let someone else do, so you can watch the screen and give instructions). I just did it myself an hour ago and the result is amazing: raiser sharp picture. The bottom one should be adjusted together with the bright and contrast pots on your breakout pcb under the controlpanel. Just fiddle a bit for best results.

Oh, and be careful, there are some high voltage carrying components nereby the black knobs, but if you are careful you should be able to turn them by hand. Never use metal tools!

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 26th, 2008, 3:43 pm

Messed with the 2 pots and there is a great improvement in the sharpness of the picture - still have that annoying 'shimmering' but the screen is brighter and more 'in ficus' than it was befor - cheers for the advice!!

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Re: Adjust Horizontal synch on my Astro

Post by grantspain » October 26th, 2008, 8:38 pm

what type of 15khz converter are you using?

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 26th, 2008, 8:52 pm

Its a j-Pac, and im running soft15khz - thing is, if i dont have anything connected to the jamma loom then the problem is the same...

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Re: Adjust Horizontal synch on my Astro

Post by ckong » October 26th, 2008, 10:25 pm

chubsta wrote:Its a j-Pac, and im running soft15khz - thing is, if i dont have anything connected to the jamma loom then the problem is the same...
Could you post some pictures or an avi of the 'shimmering' so I know how it looks? Might help for a solution.

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Re: Adjust Horizontal synch on my Astro

Post by grantspain » October 26th, 2008, 10:36 pm

sorry explain,do you get the same problem with a jamma board connected or does this only do this with the jpac running?

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 27th, 2008, 8:10 am

If i have nothing connected to the jamma board then it is still there. Its hard to describe, but see if this makes any sense.

the distortion is constantly moving, which makes it look like a sort of shimmering effect to me - the top drawing shows what it is like if the jamma loom is not connected to anything, the 2nd shows what it is like if the loom is connected. The distortion isnt so great that it causes any problems with games etc as you can probably see from the photo of it actually running - it doesnt seem to affect the pixels on the screen (although there is the absolutely tinieist bit of 'shake'), it is just a mild distortion 'over the top' of the image that is annoying because i know it is there!

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 27th, 2008, 5:48 pm

Am still stuck on this despite trying to mess with just about every pot on the chassis! Is it possible it is a grounding issue? The chassis seems to be in some sort of plastic caseing and i cant work out if it is actually connected via a green earth lead to the main machine frame (my NeoGeo has got a earth lead running from the chassis main board but this doesnt seem to have...)

also, there is this weird little black, plastic covered thing poking out at the top right of the board that doesnt seem to really go anywhere - any idea what that is?

as i look at it it looks more and more like just 'interference' on the screen as the pixels themselves dont seem to be being affected - games look fine and there is no pixel or screen distortion, just this weird distortion over the top of everything....

I have just read another site and the descritpion 'wave interference' seems apt for this. i reckon it is down to something affecting the monitor but it isnt near anything else so not sure what i can do abut it....

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Re: Adjust Horizontal synch on my Astro

Post by grantspain » October 27th, 2008, 6:00 pm

its an earth problem or noise coming through the mains
you need to check continuity from the monitor frame to the plug earth

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 27th, 2008, 6:08 pm

grantspain wrote:its an earth problem or noise coming through the mains
you need to check continuity from the monitor frame to the plug earth

cheers - and now for the newbie question....

how exactly would i do that? I have connected a wire from the earth nut at the rear of the machine to the nut on te step down so i guess the unit as a whole is earthed do i just use a mightymeter to check from the monitor frame to the earth nut on the stepdown (that shows a circuit BTW)?

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Re: Adjust Horizontal synch on my Astro

Post by grantspain » October 27th, 2008, 6:20 pm

just link a wire from the earth terminal nut to the monitor metal frame

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 27th, 2008, 10:56 pm

i connected my mighty meter to the earth on the stepdown, and touched the monitor frame and it showed a complete circuit so i guess that side of it is working ok.

in terms of mains noise, the astro has a small black box marked as a 'noise filter' inside it which i would have thought would have taken any noise out - is it possible this is not working up to spec or is it a case of it either works or doesnt work - i dont really want to have to spend money unless i know it is going to solve the problems....

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Re: Adjust Horizontal synch on my Astro

Post by grantspain » October 27th, 2008, 11:07 pm

right now do something really strange,disconnect the earth at the earthing bolt

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Re: Adjust Horizontal synch on my Astro

Post by Mr-Megalo » October 27th, 2008, 11:28 pm

if your getting a noisy picture like interference, locate the RGB wiring that goes from the monitor chassis , they may be fastened to the cable holder inside the left side of the cab that routes 110v AC up to the light, its possible that any interference could be coming from that if thats how its fastened into place

for what its worth, the line filter, PSU and monitor , even the cp too were replaced on your cab, the only thing that wasn't replaced was the actual cabinet itself - there is nothing left to replace except the JAMMA loom itself

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Re: Adjust Horizontal synch on my Astro

Post by Mr-Megalo » October 27th, 2008, 11:32 pm

just checked your pics, ac wiring is running up alongside the RGB wiring and is held into place via the cable holders

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Re: Adjust Horizontal synch on my Astro

Post by chubsta » October 28th, 2008, 7:49 am

although i had checked using a mighty meter to see if there was a connection between the cabinet ground and the monitor, i didnt actually connect a wire. i just did it now and straightway the distortion was gone so i guess it was a grounding issue :D

all i need to do now i set up a proper long term connection instead of the bit of wire i currently have and ill be all set!

thanks for the help and advice guys, really appreciated :awe:

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