two WG4900 questions

elfyhead

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i have a WG4900 in my q*bert which has had a video problem since purchase. it has some lines up and down the display (starting very closely spaced together on the left-hand side of the screen, then spacing out to about 1.5 inches between them across the rest, canted slightly to the right as they go down). i took out the monitor and the vertical section of the chassis had some burning, which makes sense as the monitor is rotated so those lines are because of something misbehaving in the VOUT part of the chassis. i re-capped it hoping that would do the trick, but it didn't.

so i can do some more testing on the chassis that is in there (riptor pointed me to testing the solders on the wire-wound resistors, for instance), but i have a 2nd chassis and i'd like to try it in there instead just to see if it might work.

i have two questions about this:

1 - the old neck board is attached to the tube with some white glue-type stuff. i've attached a picture with it circled. what is the best way to get this gunk off? i don't want to damage either the tube or neck board while removing the old neck board of course.

2 - i'm wondering what to do about the grounding strap. it's a bit of a pain since it's soldered on to the corner of the neck board. should i solder it off of the neck board in there now and re-solder it to the potential replacement neck board, or should i leave the strap on the replacement and run it around the tube?

thanks in advance.
 

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1 - the old neck board is attached to the tube with some white glue-type stuff. i've attached a picture with it circled. what is the best way to get this gunk off? i don't want to damage either the tube or neck board while removing the old neck board of course.

Just pull straight away from the tube. It will break loose. If you're paranoid, just use a razor blade to slice through it to separate it from the neckboard.

2 - i'm wondering what to do about the grounding strap. it's a bit of a pain since it's soldered on to the corner of the neck board. should i solder it off of the neck board in there now and re-solder it to the potential replacement neck board, or should i leave the strap on the replacement and run it around the tube?

Just cut the wire, then use a wire nut to reconnect it when you put it back in. You'll probably pull this out again sometime, and the wire nut will make it easier to do.



As for the lines on your monitor, try adjusting the V-LIN pot. Possibly the brightness or color, but I'd have to see the pic to confirm that...
 
thanks much - good idea on the ground strap.

the lines are in the pics below if you can see them. the straight up and down ones are camera artifact, it's the canted over ones that are real.
 

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I would start by turning the screen pot counter clockwise a little bit it's located on the flyback under the focus then post a pic

Andrew
 
I would do it with the video input unplugged, turn the SCREEN and color drives down to where you "just" get a totally black screen.
 
Yeah, looks like the blue is too high. You shouldn't have a blue background on the pyramid screens...
 
so finally got a chance to get back to this. i haven't done the trick of unhooking the video supply yet, but i just played around with the screen, and red and green outputs a bit.

first, i found that if i just turned down the overall brightness enough, i can get a black background on the pyramids with most of the lines gone (the ones on the very left-hand-side of the screen remain), but i lose the green almost entirely. the text in the opening screen is black, as is the green part of the spinny disks.

i then tried turning the brightness down even further but turning up the red and green outputs. same problem. actually i couldn't turn red and green up much because they were close to maxed out already.

i then tried turning red and brightness down and green up, but could never get a combination where green shows up enough but the background is black.

should i muck with the black level next? or green cutoff? something else? i'll try disconnecting the video input later...
 
Put all three pots back to center. Your two cutoff pots as well.

Unplug the video connector. Turn the game on. Turn up the brightness pot (or down) until you juuuuuust start to see something on the screen. If it looks nice and white, or has a grey tint to it, turn it down until everything barely dissapears and then see what your video looks like.

If it's tinted blue again, turn the brightness back down until you don't see the blue. Then turn your red up until you see it, then back down slightly until it dissapears. Same for green. After your done, turn the screen back up, to see if you have a nice white shade now.

If I were to guess, you'll probably get your best picture with the blue zeroed out, but it looks like your tube is just worn slap the hell out. Your blue is probably actually fine, your green may be the problem.
 
4900 tubes seems to need rejuving more than others for some reason, even though they usually used the same tube as the G07 and 4600. Perhaps it stressed the guns more? You may need to have it rejuved if a rebuild doesn't help...
 
OK - so i unplugged the video and centered all 6 pots, but couldn't get enough green playing with just the Green output pot.

then i played around with the cutoffs for all 3 a bit, and, voila, i'm really close! see the attached pictures. i played one game through to level 7 or 8 or so to see all the cube colors, and some are a bit off, but at least it's close, and the saturation lines are gone.

so, i can now tweak the red, green, and screen (and maybe focus a tiny bit), but i think it's very close to done.

thanks so much guys!

EDIT: i had forgotten q*bert is actually 2 colors in the game :)...
 

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