Question about Mitsubishi WT-46809 46" Rear Projection Television

1 Answer

Convergence issue - bowing rainbows on sides.

3/19/08
I'm having the same problem as a few others with the center in good focus and the edges gradually blurring with colors bowing out of sync. This has been happening for almost a year and I have assumed the problem is a cold solder joint or loose connection. When it first happened, a light tap on the top of the set straightened everything out for as long as the set was on. Eventually the tap wasn't enough and it would happen every few minutes. I have an electronics background and decided to remove the back and check all connectors for a loose fit. I replaced the back and the set worked fine for a few weeks, then started acting up again. This time I removed the back and with the power on and rubber gloves on, I wiggled each connector I could reach until the picture returned to normal. The circuit board with the large heat sink in the middle of the set seems to be the culprit and looks difficult to remove and check solder joints, so, for the last six months I've just been turning the set on and giving the heat sink a wiggle with the glove on and the set behaves for the day (NOT recommended for someone with no experience or respect for electricity!). If anybody has determined what might be loose and on which board I should look I would appreciate the heads up. Just because the problem goes away when I wiggle the big heat sink doesn't mean that that board is at fault. Other components near by also move a little since the heat sink is so long and It's board is large and flexible. I've read other solutions that suggest removing and replacing an IC, but If the problem goes away with a wiggle, it seems I may have a related but different problem. The set is at least 4 years old, but when it's working after my "quick fix" which is getting old, the picture is as sharp and colorful as new.

Thanks for any input you may have.

Woody
dtw@maine.rr.com

Posted by on

  • Speakerman Apr 06, 2008

    Thanks for the solution suggestion, Rob. It turns out that the convergence chips were the problem, but not the chips themselves. I found that 21 out of 36 total solder joints on the chip's pins were cracked and loose or cold soldered when inspected with a 10 power loupe. I was surprised since all the pins have an omega shaped spring bend between the chip base and the circuit board which should have prevented the above condition. I guess the bend should have been larger or of a smaller gage or both.



    The board removal wasn't that difficult. The whole assembly of circuit boards pulls out like a drawer after removing a few screws, wire keepers, several connectors, and high voltage leads. I found a very good pictured tutorial on the process on ecoustics.com. In addition, it would be helpful to take digital photos of connector locations before removal so nothing is missed on reassembly (a sanity check). I found that most of the connections only fit one location by shape or length except the high voltage leads. I marked them with tape before removing. It's also a very good idea to vacuum the assembly brushing carefully with a long bristle soft 1" or so paint brush while holding the nozzle near to collect the dust. This helps prevent dust from getting on connectors and preventing a good re-connection as well as allowing the operating heat to escape more freely. The typical round brush attachment is too big and course to safely and effectively do the job.



    Once the board was out, cleaned, and inspected, I re-soldered all the pins and a few other suspicious joints with .022" silver bearing solder and a small iron, and reassembled the set. It now works and looks as good as new, very bright and sharp. A well spent afternoon!



    Woody

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I just fixed my convergence problem on a Zenith 60" rear projection.
I replaced the IC's and removed the convergence board to do so.
Those IC's have up to 18 connections for each one so you may have some loose connection points if we are talking about the same board. The IC's are connected to the largest heatsink for my TV, if you look from all angles, one view should get you a view of the 2-3 IC's present. Most people will tell you to completely remove the convergence board and check all the big resistors on board as well. Fuses are always a good option too. If you can solder well I would unsolder and resolder the IC's at the very least, but it is only a suggestion on my part. I am not a TV technician but an ATM/Computer tech. The boards look like only a sign from God will get them out but can be relatively easy.
Let me know...

Posted on Mar 19, 2008

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1 Answer

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