Intermittent Traces

[SavannahLion]

My LCD flat screen has weird behavior. 90% of the time, if I push the screen one way on a specific side, half the screen goes to crap. If I push the screen the other way, it clears up. Somewhere there's a bad connection. I can tell it's going to be an all day thing.

So while I'm getting my materials together and trying to shoo the curious kids away and trying to explain to the wife why the baby is sucking on the spool of solder, I realized that I never asked this question.

If a trace (not a soldered joint) has a intermittent connection due to a cracked PCB, is the correct procedure to completely severe the trace and add the jumper or just add the jumper and be done with it?

I repaired two minor control boards that had cracked substrate without cleaning the cracked area and now I'm wondering if I did those repairs correctly. They seem to work ok during tests but I haven't installed them so I don't know if they're reliable repairs.

[lilshawn]

f a trace (not a soldered joint) has a intermittent connection due to a cracked PCB, is the correct procedure to completely severe the trace and add the jumper or just add the jumper and be done with it?

well, i use glue to reinforce the board so further flexing will not cause it to break again. then depending on the extent either jump it, or just bridge it with solder.

judged by your description, you likely have a loose plug that feeds the LCD panel itself... is a wide single edge connector,  it will be the only one going to the panel. it's common to get worked loose and cause all sorts of issues.

[SavannahLion]

That's what I figured on the cracked PCB. Those repairs I did are low frequency applications. One is the control board to a joystick if that gives you any ideas.

If that's the case it'll be oodles easier than trying to replicate the problem with a powered PCB.

[ChadTower]

Add the jumper.  It's just not worth the extra time involved with guessing.

Of course, in something that small and SMD, I would probably just get the part number off the PCB and head to ebay.  There is a good market for used TV PCBs given how many of these TVs fail prematurely.

[SavannahLion]

Add the jumper.  It's just not worth the extra time involved with guessing.

My question was, do I need to ensure the trace is completely severed or do I just leave it?

[lilshawn]

Unless its obviously going to cause an issue (track is lifted or carrying high voltage very close to another track, there is no reason to mess with it.

In my examples I would either peel up the lifted track and cut it off or paint it with some clear nail polish to insulate it, and only if I considered it a risk of shorting out.

If its low voltage don't waste your time. Usually if its close enough to short or spark, it low enough voltage to not spark in the first place. (If that makes sense)

[MonMotha]

On high resolution panels, the image is sent in two parts.  If EXACTLY half your screen is going bad, you've probably just got a bad connection at the input cable.

As for trace repair, yeah, just tack a jumper down over it if you can find the bad spot.  The shorter your jumper, the better.  If you're concerned about high speed, try to make your jumper follow the path of the original.  The impedance still won't be right, but it'll probably be fine.

I repair tiny stuff on high density SMT boards all the time.  It just takes a steady hand, a good iron (small tips are helpful but not required, believe it or not - good temperature control and sufficient power are more important), tiny wire, and some practice are all it takes.  I routinely rework stuff so small I can't see it clearly without some magnification, and I've got better than 20/20 uncorrected vision.