Grounding with in-line EMI filter

DuffCon

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So I've been having an issue with a slightly wavy monitor. My chassis is fully rebuilt.

I searched around and found that a bad ground might be the issue. Looking at my setup I see line power with ground coming into a EMI filter. It leaves and goes into a distro block with a fuse inline and sends power to the isolation transformer.

25d0b246f23a13b08a4b83098aa13463.jpg


It's odd there is no ground after the EMI filter and the FG for the power supply is jumped to the input grounds.

17d2b70c4c7a74cbbfffa9fc76cb6d6e.jpg



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So my question is "is this ok" or should the FG be grounded directly to the outlet?

If it is "ok" then is a bad PS the cause of my wavy picture?
 
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your AC and DC grounds shouldn't be tied together. FG is the AC ground and its tied to the DC ground.
 
Field ground going into the filter is a wire (normal).

Going "out" FG is just tied to the metal filter box where it is mounted.

The filter is mounted to a bigger metal box, that may be sourcing your field ground?

Some people tie the power supply field ground to DC ground due to noise problems in the video signal. Opinions vary on doing this.
 
Yeah. Midway definitely did this (tying Field Ground to DC Ground) from the factory in MK2 cabinets. It's even printed out as such in the manual for it.
 
So if the grounding is "OK" then possibly bad A/C cord or PS? Forgot to mention some audio static too (tried multiple PCBs with same results, slightly wavy screen and audio static when there is no music sound being played)
 
Have all of these grounded:

-Line Filter case
-transformer case
-control panel
-Marquee light
-coin door
-chassis
-on off switch
-monitor frame

Good rule is anything metal that does not reach the PCB.

I would not have the speaker grounded because it runs to the board.

Anyone concur?
 
Assuming all this is grounded correctly; would it be reasonable to assume that the Power supply is faulty? This is probably the original and it is loud (vibrates, has no fan). So i'm wondering if simply swaping it out is worthwhile.

Have all of these grounded:

-Line Filter case
-transformer case
-control panel
-Marquee light
-coin door
-chassis
-on off switch
-monitor frame

Good rule is anything metal that does not reach the PCB.

I would not have the speaker grounded because it runs to the board.

Anyone concur?
 
read this thread. https://forums.arcade-museum.com/showthread.php?t=201112

often FG and Logic GND are tied together anyway. Either via video gnd to monitor and then monitor to frame to FG or somewhere else. I have had scenarios where connecting FG to Logic gnd on power supply fixed monitor interference, I have had the opposite as well. I am not an electrical engineer so just can go on what others post and my own experience.

If you monitor frame is obviously tied to FG with gnd cable, I would try jumpering PS Logic GND to FG and see if interference goes away. If it doesn't, try the opposite.

BTW most speaker metal is/should be tied to FG.
 
I'm not sure what a The PS logic ground is?

If it's the ground that's not the field ground then it already is jumped on my PS.

Are Power supplies supposed to hum loudly?
 
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I'm not sure what a The PS logic ground is?

If it's the ground that's not the field ground then it already is jumped on my PS.

Are Power supplies supposed to hum loudly?

Yes, and you're right it is jumpered.

Some power supplies do hum loudly.

If you have another power supply to swap in to test if your problem goes away, I'd try that next.
 
I'm not sure what a The PS logic ground is?

If it's the ground that's not the field ground then it already is jumped on my PS.

Are Power supplies supposed to hum loudly?

Again others can jump in with more correct info. Logic GND is your 0v DC reference.

Sorry, yes, your PS has logic gnd tied to FG via jumper. However your PS FG is not tied to Earth GND but am pretty sure it should be.
1) Try taking out the jumper
2) try with jumper and adding FG to EarthGND connection
3) try no jumper between logic GND and FG but with FG to earth GND.
4) if monitor has a Earth GND connection to frame, try removing it to see what the behavior is.

I wish I knew the rhyme or reason but don't believe anyone has posted anything to explain this. We all know FG and Logic GND should not be tied together but also know, in most games, it is somehow via the Monitor and when you put a switcher in you get these weird issues.
 
So a quick update. I messed around bit tonight, tried a new PS, new power cable and no help. Also tried connecting FG to earth ground (assuming earth ground is the metal plate the Noise filter is attached to). Did not try disconnecting the jumper between logic ground and FG and moving the jumper to earth ground.

It's gotta be a grounding issue, I have another cab in the same outlet with no issues...
 
So a quick update. I messed around bit tonight, tried a new PS, new power cable and no help. Also tried connecting FG to earth ground (assuming earth ground is the metal plate the Noise filter is attached to). Did not try disconnecting the jumper between logic ground and FG and moving the jumper to earth ground.

It's gotta be a grounding issue, I have another cab in the same outlet with no issues...

You should post a picture of the symptoms

So we can see

If it is what I think it is

On the old midway games

You need to replace the line filter

Or bypass it

it's not need at all

Earth ground goes to the chassis major

Parts of cabinet and FG on switcher.

And not hooked to the switcher dc ground at all
 
Here's a vid of the picture; it's hard to capture because it's so subtle.

http://www.youtube.com/watch?v=4xrctBzvTHk[/QUOTE

You may have a different symptom

It's very easy to see the noise in the video

When the filter is bad

You could still by pass it if you suspect it.

Can it be seen in brighter images?

Can you still see it with no game signal

Just in a raster?

Is only only the sides of image or

All through the image.
 
It would be easy to bypass the EMI at the distro block. I'll give that a shot tonight
 
Update; took EMI out of the circuit, ran new A/C cord directly to disto block. Same issue. Is it possible to have a bad isolation transformer?
 
Its a little hard to pin point

But do you have similar issues with a test pattern

Generator outside the game

That would isolate it more

Need to confirm it's only in the monitor

Can you swap your iso with another game

So you can rule that out.

I would not suspect it.

It can be a big advantage to have a known

Working bench setup

It maybe easy to track down with a o-scope

But. If everything else is good

You might try also another regulator

Next. Even the new ones are an issues

Sometimes.
 
So an update; I ran into another issue with this chassis where I was having some flashing blue on the screen.

https://forums.arcade-museum.com/showthread.php?t=432541

I think i've got that under control, but one thing I noticed is that when I swapped the chassis on this monitor is that the picture was rock solid, no warbles at all. When I was T/S this issue, I went through the cab and verified proper grounding, but when put the original chassis back in after repair, the warble returned....

I don't the issue is related to the filter or grounding at all. On a positive note, I learned a lot and some mild audio interference was resolved.
 
FG is earth ground - all metal parts are tied together and goes to FG plug on power supply and then goes out to third prong on outlet plug into wall


don't like the 3 power wires laying on top pf the fuse holder like that. one wire looks like its touching the one end of the bare fuse holder with only the insulator of the wire in between. could be some electromagnetic field is causing interference. I would move that fuse holder over an inch or two and bend those wire up so they aren't laying on the fuse holder and see if that helps.

then try it without the FG to ground lug tie and see if that changes anything

if all that doesn't change anything I would try another monitor and see if some problem in the monitor causing interference good luck
 

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