K7000 new cap kit & flyback, still have faint snow

mrbippers

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K7000 new cap kit & flyback - now blowing fuses

First I want to thank all the contributors to this board. After installing a new flyback and cap kit on my wg k7000 I blew a fuse right away on the first startup. Some searching around revealed similar problems could be attributed to a lack of the insulator between the HOT and the chassis. I had used some arctic silver since the old one was just held on by thermal compound but after swapping it out for some rubber wire jacket I'm back in business.

The cap kit/flyback took care of most of my issues. Vertical waves are gone and the colors are popping. However, I still have a faint 'snow' in the background. They are faint diagonal lines that blow across the screen at varying speeds sort of like drifting snow in a storm. It's the sort of thing I can live with if I have to, but maybe there's something else I can do to address this?
 
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Posting a picture of this "snow" might help someone diagnose this.

Personally the only time I have seen "snow" was a game board issue and not a monitor issue.
(but that may be my interpretation of "snow")
 
check your +5 and see if you have any ac ripple on it.. when power supplies stary getting flakey you will get this effect alot. im not saying thats what it is, but thats PROBHABLY whats up..
 
Yup, it's a power issue, probably nothing at all with the monitor.

5v from the power supply, or it could be that you need a ground wire hooked up to the frame of the monitor, or removed from the frame of the monitor. I've seen coin door lightbulbs make snow appear on the monitor too, if the bulbs are tied into the wrong line sometimes it doesn't like it.

If it's a switcher try swapping in a power supply out of another game and see if you get any change.
 
One easy thing to try would be to tie earth ground to logic ground. Its really common for switching power supplies to have "noise" within their outputs that can be seen on the screen as snow.

Matt
 
One easy thing to try would be to tie earth ground to logic ground. Its really common for switching power supplies to have "noise" within their outputs that can be seen on the screen as snow.

Matt

I agree on it being an earth ground issue. Do you have a green wire for earth ground running to the monitor frame? Does your power cord have three prongs?
 
Also, check the video ground wire leading up to the monitor. I had a similar problem on Smash TV where the video ground (a screened ground around the shielded cable) was broken right near the connector at the monitor.

-Ian
 
snow.jpg


This was the best picture I could get. I need to adjust the red convergence too. The previous owner of the cab had rewired it without connecting the filter (or fuse and power switch) so that's probably not helping. The ground to the monitor frame isn't the best connection, so that needs to be moved/tightened. I also need to trace back the wall outlet but I wouldn't be surprised if it's an ungrounded outlet--house was built in 1901. I had rewired a good chunk of my house, but not this room.

The monitor went dead shortly after taking this picture and blew a fuse, but I'm thinking it's because the rubber I used behind the HOT had completely cut it off from the heatsink and it overheated, at least that would explain the burning plastic smell. Hopefully nothing is permanently damaged. I'll pull the HOT to test it and reconnect with a mica insulator or as close as I can find at Radioshack.

Now to rewire the AC in with the filter, secure ground on monitor frame, rewire outlet to grounded circuit, and hope an overheating HOT was the only problem with the monitor chassis. I'll bring back an update when that's all taken care of. Thanks.
 
One step forward and two back. I pulled the HOT, checked okay. Replaced with mica insulator and thermal grease. Fired the chassis up and 'doh' had the center pin on the HOT touching the heatsink so I got a nice little glow and blew the fuse. Pulled the HOT yet again and still okay. Reinstalled making sure the legs don't touch. Still blowing fuses when powered up. Pulled both the HOT and C36, neither are shorted.

So, knowing that all this started with the HOT touching the heatsink or when it overheated, what's the next series of things I check? Start with the VR?

Also with the original big green four legged C36, which way does it go back in--the side with the text facing towards or away from the flyback (in my haste I forgot to take note).

UPDATE: Looks like I have burn marks on C33, guess it might be best to start with replacing that.
 
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Replaced C33 and found shorted R103, R104, R105 so far. Also reading a short between the traces for the 1st and 3rd pins of the HOT and the heatsink. This is with R103-5, HOT, and VR all pulled. Any likely candidates for this or perhaps the better question is at what point do I decide it's no longer worth it and cop out for a CGA to VGA converter?
 
So the monitor is working again! R103-104 failed beep test but are within their ohm specs. R105 is also 8 ohms at room temp so that was fine. Wound up replacing the HOT from the kit with the old one and swapped the 2a fuses I had been using for the 5a in the schematic.

Turns out the 'snow' I was describing earlier would be more accurately described as herringbone interference. Jumpered the FG and Ground on the switching power supply and a problem no more. Also checked the PS as cadillacman suggested and while it wasn't fluctuating, it needed some tweaking to bring the 5/12v closer to spec.

That leaves me with the convergence issue. I went to start playing with the rings and it looks like they're so old and brittle that they're literally falling apart. Not only are the tabs gone but the rings themselves are severely cracked and keep shedding pieces. At this point is that something I could possibly replace or should I be looking to just swap in a new tube (it's only a 13" monitor so pretty easy to find)? If I am swapping tubes what should I be looking for other than a neck with the matching number of pins?

rings.JPG
 
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