moving diagonal lines on monitor

charmcello · Joined: 19 Jan 2010 Posts: 4

In general, what typically causes moving diagonal lines on a monitor? The space between the lines changes. Sometimes the lines are spaced far apart and then they get closer and closer and move faster and faster. And then they go back to being slow and wide apart.
The lines are light in color (white?) and are most noticeable when the picture is somewhat dark.
Other than that, I've got the picture looking great. (I'm a brand-new repair tech - so any general suggestions or advice or resources about electronics trouble-shooting and repair would be most welcome!)

vtech · Joined: 08 May 2006 Posts: 1264 Location: USA

Number of possibilities;
Based on your description, sounds more like an interference. Could be internal (such as switch mode power supply radiation) or from an external source which can be rather difficult to find. I have seen something similar to your description on a relatively new unit and it ended up being a nearby CFL light.
The reason for the change in speed is usually indicative of a change in frequency of the interference beating against horizontal & vertical scan rate.
Best to try to isolate the problem by unhooking from any external device first.

charmcello · Joined: 19 Jan 2010 Posts: 4

I'm fairly certain it isn't external interference because it's not an intermittent problem and I've had the monitor in two different locations in the shop when I've tested it.
How would I find internal interference?
Could it have anything to do with a wire looped around a coil of the flyback transformer? I did have to resolder that wire when I switched out the transformer.

jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

Try turning down the SCREEN control on the newly changed flyback?
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charmcello · Joined: 19 Jan 2010 Posts: 4

Hmmm... the only controls on the flyback transformer are contrast and focus.

charmcello · Joined: 19 Jan 2010 Posts: 4

Oops sorry. I wasn't at the shop when I posted that last message. Yes, there is indeed a SCREEN control on the flyback. We did try tweaking that, with no change.

joester · Joined: 03 Dec 2009 Posts: 35

If we're talking CRT monitor, it could be that the signal gun isn't off during the sweep return.
Again, if we're talking CRT, probably not worth looking for a repair, since component level diagnostics would be as expensive as a new LCD monitor. Your only hope would be if that make and model has a known and previously diagnosed problem with the cure posted somewhere on the internet.

If this is LCD and it has the "return sweep" (which does not exist in LCD) then I would clean the circuit board well with Alcohol paying particular attention between the leads of the fine pitch SMT chips. Try soaking the undersides of the chips and blowing out with compressed air. There could be some solder residue around the heel of the lead causing signal transfer from one lead to another. Check all ground points and solder joints carefully.

Joe