Model# ws-55805 mitsubishi tv HD

I had the exact same problem. I read the posts - jiggled the large heat sinc and saw the instant improvement of the convergence - intermittently - (the most helpful posts by FFJim and MikeNJ1964 thank you!). I then got a copy of the repair manual (online) and isolated the two Convergence Power Chips IC8D01 and IC8D02 according to the repair manual and are parts HIC-STK392-040). I was able to use an alternate way to get to the cold solder joints (broken solder points) on the bottom of the entire motherboard (all three boards) assembly (without removing the middle board) by removing many of the cables (9 or so) and leaving just the tube cables in the back right corner connecting the RGB complex. After removing the cables, and unscrewing the 3 wood screws holding down the plastic (black) housing holding the main boards, I was able to slide out, lift and twist the motherboard assembly on it's side while leaving the RGB complex cables at their location. Looking at the bottom of the motherboard assembly (inspecting all the solder joints) I found the area of cold solder connections for the STK392-040 by seeing where the two Mitsubishi WS-55805 IC8D01 and IC8D02 solder points were located. It appears the reason these solder points get loose is becaus of the large Heat Sinc they are connected to would heat up, lean and will break loose with movement of the TV. By just re-soldering the cold broken lead points (which were visible) it repaired my unit entirely. This can be done at home with just a simple solder iron and solder (make sure you heat the lead and solder pad and apply the solder to the hot area (not the iron). I had to do that to about 6 of the 30 or so leads. Then, I retraced my steps assembling the unit and it worked great!
Here is an image of my main board assembly from the manual.

When the 3 colors no longer line up and the sides are all curved, the convergence circuits have stopped working. Usually the convergence output IC has shorted out and has overloaded the convergence power supply which stops working. The output IC (usually STK393-110)should be replaced, the power supply restored and the convergence circuits realigned by someone experienced in Mitsubishi projection sets. When I make a housecall for a set like that I charge $150, but shops in your area will vary so ask around.

I soldered the cold solder joints; didn't fix it. Then I replaced IC8D01 and IC8D02; didn't fix it. All resistors looked good. Then I noticed that F9A23 (5A) was open on the pcb next to the convergence pcb. It was standing up with a .22 ohm resistor connected in series. I replaced the fuse and that fixed it! I suspect that the original ICs were okay only needing the cold solder connections soldered and the fuse replaced.

I fixed mine today! I found solder was not making a good connection on the convergence board ( middle green board ). If you pull off the back cover, there are three boards. Carefully remove the center board, there are several screws and plugs. You will have to remove the three bolts holding the large heat sink in, the two pieces that sit against that board had a bad connection at a few of the pins. I took the board to a local electric store ( Mayfair Electronics ) and they soldered the connections for $30.00. Works great now!!!
Note! If you want to make sure that is the problem before tearing your tv apart. While the tv is acting up put some slight pressure on the large heat sink by pulling or pushing and see if your picture straightens out.