WG2774 flashing white dot - video and pics in post

[David111]

I have ordered a cap kit.
I have resolderd a lot of points on all boards.
No visible problem with fly back, but I have ordered one just in case.
There is ticking and a pulsating high-pitch whine accompanying the flashing.
Video link at bottom.


I'm not sure about the brown caps. Maybe it's a mod for something?

The tube appears to be a 25". Apparently the 2774 was not intended to work exclusively with a 27" tube?

Anywho.... now the video

[lilshawn]

change the caps.

but also just for now if you have one, try changing c117. (it's tucked in the corner of the heatsink by the giant 400v 210uf cap). it's a feedback capacitor that helps regulate the power. if its no good the voltage can drop out and do all sorts of weird things.

[David111]

After the cap kit and after replacing one of the three brown caps my screen is now stable. Problem now is below:


The Degaussing wire is unplugged here. I had it plugged in when I first powered up. Either way, the screen looks the same. The relay? that controls the output for the degaussing is always hot to the touch whether the connector was attached or not. It shouldn't be, correct? And if it were shorted to "on," wouldn't I be getting a continuous active degaussing effect on the screen?

[lilshawn]

the dagausser "box" has a couple of resistors in it.

one increases in resistance when the temperature rises...the other a high wattage resistor.

basically voltage gets dumped into the high wattage resistor on startup. the resistor converts it to heat. at the same time, the same voltage runs through the degauss coil on the tube and back through the variable resistor. because LOTS of current flows through it, the coil performs the degaussing.

all the while the high wattage resistor gets hotter, in turn heating up the variable resistor....the resistance starts going up...less and less and less current flows through the degauss coil until nearly nothing flows.

it's warm by design. it's also self resetting (after about 15 minutes of cool down time.)

[MonMotha]

It looks like it's generally working and just needs the color gain/cut-offs adjusted.  This is not uncommon after a full re-cap.

SOP:
- Set brightness and contrast to middle
- Adjust screen appropriately if it's unreasonable (crank it until you get retrace lines, then back it off until black is black)
- Adjust the color gains so that red, green, and blue are roughly equal in intensity on the high point on the ramp or use a colorimeter to get the white point you want and nothing is overdriven
- Adjust cut-off so that the bottom 5-10% of each ramp is invisible
- Iterate back and forth between gain and cut-off until you get something reasonable
- Tweak brightness/contrast to taste, if necessary (you've basically defined these as "correct" at the mid-point)

Gains and cut-offs are typically on the neck board.

In particular, it looks like your contrast/gain is way too high, especially on green.  I don't know what that test pattern is supposed to look like in order to tell you if brightness is reasonable, and the picture may be misleading, too.  That red doesn't really look red, but I assume that's a camera artifact since I don't see any purity issues.

[David111]

Thanks for the clarification on the degaussing operation. I used a soldering gun and was able to convert the purple parts of the screen to red on Sunday. I left the game on in the garage and let the boys play it. All seemed fine up until the point I turned the game off for the night. I powered it up on Monday afternoon and it's back to the original flashing problem.

Monmotha, I hope to be able to make the recommended adjustments soon. Right after I figure out the flashing deal. Any suggestions regarding that issue? I installed a "Bob Roberts U2000 to K7500 Combo Cap Kit" FWIW.