WG U2000 Contrast

srarcade80

New member
Joined
May 16, 2008
Messages
567
Reaction score
6
Location
Orlando, Florida
Having a hard time fixing a contrast problem on a U2000. If I turn the contrast and brightness anything less than full blast, the color goes away completely and its black and white only. With contrast and brightness on max, there is faded color, but any screen with high amounts of white trigger it to go darker, until you touch the bightness/contrast pots again.

Could this be an aging flyback?

Heres what I have done:
1) Capped the chassis
2) Tinkered with screen voltage
3) Replaced U500 (RGB Amp) on neck board with a new one
4) Switched to another compatible and known working tube with good guns
5) Switched the satellite controller to another one (this actually has fixed a few in the past)

I'm stuck! Any more ideas?

Thanks!
 
Resistor R811 is bad. Should be 100k.

Just gave that a try, same result.

EDIT - Just found the U2000 troubleshooting guide:

BRIGHTNESS R817, R811, C805, C810, R823, R824, IC U500 15KHZ - R823 25KHZ - R824
CONTRAST R901, R902, VR905, IC U500

My readings:
R817 (47k) - shortd (open)
R811 (100k) - short (open)
R823 (3.0) - 3.2
R824 - N/A
R901 (2.7k) - 2.2k
R902 (2.2k) - 1.7k

So it seems the suggested resisters are just about all having problems. I suppose you have to change them all in one shot to prevent another from going bad. After I replaced R811 (100k) by itself, it went bad immediately.
 
Last edited:
resistors don't short......they burn till they open and the cause is to much voltage is present. Check your b+ reading and verify that it is over voltage.....usually around 125 vdc.
 
mod, do you just use logic ground for that? as in, the ground pin in the video header. that's how I did it before. had a 7500 that would go into shutdown cause the B+ was off, been fine ever since I did that.

also, is it DC or AC? I always forget. heh
 
mod, do you just use logic ground for that? as in, the ground pin in the video header. that's how I did it before. had a 7500 that would go into shutdown cause the B+ was off, been fine ever since I did that.

also, is it DC or AC? I always forget. heh

DC - and I just clip my black lead to the monitor frame when measuring.

Just make sure you don't measure it on the pin up near the edge labeled Video B+ (TP203). It has a completely different voltage (156)...
 
If the other parts test good and all the caps are in the correct place.
Did you adjust the subcontrast next to the remote board
connection to the chassis, clockwise for more contrast.
It says cont next to control..
And good connections on the plug connect cn501 on the neck board
and confirm that r510 is good. And Z500 has a good 12v's on it.
 
hey, have you fix it. I have the same problem with my u2000.

best regards
big boss
 
Just gave that a try, same result.

EDIT - Just found the U2000 troubleshooting guide:

BRIGHTNESS R817, R811, C805, C810, R823, R824, IC U500 15KHZ - R823 25KHZ - R824
CONTRAST R901, R902, VR905, IC U500

My readings:
R817 (47k) - shortd (open)
R811 (100k) - short (open)
R823 (3.0) - 3.2
R824 - N/A
R901 (2.7k) - 2.2k
R902 (2.2k) - 1.7k

So it seems the suggested resisters are just about all having problems. I suppose you have to change them all in one shot to prevent another from going bad. After I replaced R811 (100k) by itself, it went bad immediately.
Having similar issues, but looking at the schematic and none of these are adding up to what I see.

R817 is listed as 470k
R811 is listed at 47k (I realize there are many revisions and debate on this one)
R823 is listed as 1.5
R901 is listed as 3.3k
R902 is listed as 4.7k

This is from the schematic posted Here.

Can anyone shed light on this? I went and bought a bunch of resistors based on the above post and I'm not sure it's the right way to go. Should I just follow the schematics instead?
 
Having similar issues, but looking at the schematic and none of these are adding up to what I see.

R817 is listed as 470k
R811 is listed at 47k (I realize there are many revisions and debate on this one)
R823 is listed as 1.5
R901 is listed as 3.3k
R902 is listed as 4.7k

This is from the schematic posted Here.

Can anyone shed light on this? I went and bought a bunch of resistors based on the above post and I'm not sure it's the right way to go. Should I just follow the schematics instead?
I don't have a U2000 handy, but if your board values match the schematic and the resistors on the the board look like they haven't been changed, I would go with that. Be sure to remove, or lift one end of, resistors before checking them so as to get an accurate reading.

The key problem with no color on these WG chassis is loss of the automatic brightness limiter (ABL) pulse to the neck board. Commonly, this is caused by R811 being open or of a very high resistance compared to its original value.
If you have an oscilloscope, you can check if this pulse is reaching U500 on the neck board and track down where it is being lost.
 
I don't have a U2000 handy, but if your board values match the schematic and the resistors on the the board look like they haven't been changed, I would go with that. Be sure to remove, or lift one end of, resistors before checking them so as to get an accurate reading.

The key problem with no color on these WG chassis is loss of the automatic brightness limiter (ABL) pulse to the neck board. Commonly, this is caused by R811 being open or of a very high resistance compared to its original value.
If you have an oscilloscope, you can check if this pulse is reaching U500 on the neck board and track down where it is being lost.
Thanks for the input. I've been screwing around with resistors for a couple days in my spare time and honestly I think I'm making things worse. Tonight I'll go back to square 1 and start over. Interestingly my r811 was something like an 86k ohm. I've heard of 47k, 75k, and 100k being used. I put a 100k in there based on some advice on these forums and it made the picture worse, too red, and blurry on the top and bottom edges. Schematics say 47k so I'll swap that out and see how she goes when I get time this evening, hopefully I didn't break something else. I don't have a scope unfortunately so I'll have to resort to trial and error at this point until I can track it down. I've swapped neck boards with one I know is good from a k7500 so at least I know the U500 is good. At this point I'm starting to look at the tube with a bit of suspicion. This one's been a real head scratcher for me I just wish there was better documentation.
 
Okay we're all good. It turned out to be a mix of things. My chassis preferred a 47k resistor at 811. The u500 chip on the neck board was bad. Thankfully I have a couple k7500's sitting around so I was able to simply swap out the whole board easily. And last but not least, the b+ was sitting at 109v. Someone had removed the adjustment pot and replaced it with a resistor. Once I swapped that out and dialed it in to 117v with the new neckboard, it started looking really, really, REALLY good. Thanks everyone :)
 

Attachments

  • IMG_3346.jpeg
    IMG_3346.jpeg
    1.2 MB · Views: 8
  • IMG_3349.jpeg
    IMG_3349.jpeg
    1 MB · Views: 8
  • IMG_3343.jpeg
    IMG_3343.jpeg
    1.2 MB · Views: 8
Okay we're all good. It turned out to be a mix of things. My chassis preferred a 47k resistor at 811. The u500 chip on the neck board was bad. Thankfully I have a couple k7500's sitting around so I was able to simply swap out the whole board easily. And last but not least, the b+ was sitting at 109v. Someone had removed the adjustment pot and replaced it with a resistor. Once I swapped that out and dialed it in to 117v with the new neckboard, it started looking really, really, REALLY good. Thanks everyone :)
I didn't remember the U2000's R811 value, but I knew it wasn't 100k (the U5000's is!) according to schematics it is in fact 47k. excellent work.
 
Back
Top Bottom