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WG U5000 Monitor - Vertical Collapse


SNESNESCUBE64

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The U2000/U5000/K7*00 series of monitors are some of my least favorite monitors to work on. They produce a nice image when working, but that's the tough one, they have a lot of flaws. For example, they drive the neck transistors really hard, causing them to get really hot and singe the neck board, which makes it a nightmare to replace the transistors because the traces pull right up. It also has a pretty flawed design with the vertical deflection circuit. The way it derives the voltage for the the 30V rail is from a winding on the flyback, however the problem is that sometimes that voltage gets too high and goes out of spec, burning up the transistor and sometimes components on the way.

That where the problem with this chassis comes into play, it shows a classic case of vertical deflection failure.

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The first thing I did was replace all the electrolytic capacitors (all arcade monitors can benefit from a quality recap). I noticed that some of the capacitors were bulging out, which could imply failure or close future failure. Unfortunately, replacing the capacitors did not fix the issue at hand.

After that, I checked the 30V rail, there is a super convenient test point right near the vertical deflection IC. When tested, it showed that it was receiving no power. Great, this narrows it down to R303, D302, or the flyback.

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First thing I did was check the diode since that was next in line, it tested as if it was a dead short (I could even see damage where it got hot), so it needed to be replaced. It is a cheap 1N4937 diode that I was able to obtain locally. While I had it apart, I also checked R303, and that had drifted far out of spec, so that needed to be replaced with a 2 watt 1.2 ohm resistor. I didn't have that on hand, so two 2.7 ohm resistors would be close enough for this. I made sure to raise these components up a little bit so that way if they go bad in the future it won't singe the board. For some reason it also had an extra resistor after the diode, it didn't really make sense and didn't belong anywhere in the circuit. The IC in the picture was just an extra deflection IC because I was about to replace that next.

 

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After replacing them, we finally had vertical deflection, and it was looking pretty nice. I also did some preventative maintenance such as replace R111, as that it looked like it got super hot as the coating was flakey. 

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