Possible Cold Solder Joints, Help to interpret photos ?

[kumasan]

I have a plasma TV set that I am having some intermittent problems. Its occasionally powering off and not restarting until the TV sits for a while.

It was recapped with Panasonic FC/FM's that did not solve the problems and have a separate post that has more details:

https://www.badcaps.net/forum/showth...382#post729382

Im now inspecting the PS board and have attached some photos below that show some of the more suspicious solder joints. None of the joints seem at all loose or not solid. Im not sure if a cold or ringed solder joint could be the source of the intermittent problems Im seeing.

In the images below there are two fets where the vertical cuts are in the board. The FET on the right seems to have some ringing on the left most pin that looks suspicious.

The FET on the left center pin seems to have had some rosin crusted and a somewhat hazy shell.

Would greatly appreciate any help in interpreting the images of the joints.

Im planning to replacing the remaining large high voltage caps and retouch the solder joints but with the intermittent nature of the problem it is hard to tell if I got the problem.

Appreciate any feedback or tips.

Kuma

[goontron]

Re: Possible Cold Solder Joints, Help to interpret photos ?

Although that center giant blob looks horrid, failing components can do this as well. One way to tell is to lightly press on the board on different points with some plastic or wood utensil. Not to hard though, just a small amount of flex will show any problems.

[eccerr0r]

Re: Possible Cold Solder Joints, Help to interpret photos ?

They don't look that bad to me, they look like they have manually inserted vias in them, and not cold solder joints?

[PeteS in CA]

Re: Possible Cold Solder Joints, Help to interpret photos ?

Not having them in front of me, I would say that several look suspicious. Some look like they have trapped air bubbles. At least one looks like somebody touch-up soldered the joint but didn't melt the whole blob of solder.

With SMT and modern solders, detecting a cold solder joint can be difficult. I use an assembly microscope and look for an actual crack around the whole solder joint. Shadows and reflections complicate that process. Doing a good touch-up solder job and seeing if it works might be your best path.

[Mint Waxed]

Re: Possible Cold Solder Joints, Help to interpret photos ?

Judging from the large board traces and spacing, this looks like a Heath Kit or Knight Kit etched board some ham radio hobbyist threw together. If you suspect any cold joints, resolder them.

[ReeceyBurger123]

Re: Possible Cold Solder Joints, Help to interpret photos ?

I see a couple that look bad tbh, guessing its a Samsung or Lg Plasma ? If so resolder the fets on heatsinks etc.

[petehall347]

Re: Possible Cold Solder Joints, Help to interpret photos ?

look for the crack around the lead . then try moving the lead .if its bad you will see it move around . if in doubt remove old solder and redo the joint .
ps i see a definite bad one with long lead poking through .