Lg 50pg20 secondary fuse grounded to heat sinks

[KevinCro]

I have been trying my best to find out why my fuse is grounded to the heatsinks. I have bought the repair kits from shop jimmy and the fuse is still shorted. I will upload pics if necessary but I wanted to ask first if there was a specific component that would short to the heat sinks when it failed.

[KevinCro]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

I have uploaded a top and bottom view of the psu. I have circled a few components that I think are acting strange. On the top view I have circled an IC that i replaced from the kit I bought at shopjimmy. I have circled the bottom view as well. I have drawn a line along a circuit that, if desoldered, fixes the short. Moving down the line I removed the diode that is circled and it tested fine. After I resoldered the diode, the fuse was no longer shorted. However, when I went to screw the ic to the heatsink, the short came back. This makes no sense to me, but hopefully it will to you guys. Thanks for your time and help.

[vinceroger69]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

is there a insulator pad/washer missing from the ic to heat sink?

[Caleb]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

that ic appears to be a integrated fet and switching controller, did you install the entire repair kit? or just this single part? I would suspect those large transistors if your looking for a short (Q601, Q602, Q801, Q802)

[KevinCro]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

I replaced all of those transistors and several capacitors. When I removed the resistors there was some tape that held them to the heat sink. Were those the thermal pads that you are talking about? The kit didn't come with any so I just used thermal paste.

[budm]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

"When I removed the resistors there was some tape that held them to the heat sink." Can we see the picture of this resistor? It sounds to me like the insulator sheet is missing.

[KevinCro]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

This is the front and back of two of the components that I removed. These both had the tape on the back.

[KevinCro]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

This is the front

[budm]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

They are not resistors, you need to put the insulator/thermal transfer pads back in place.
If you check the resistance between the center leg and the metal plate, it should show <1 Ohm.
I hope the power supply is not damaged.

[KevinCro]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

I mistyped resistor. I haven't hooked it up since I replaced them. I just checked to see if the fuse was shorted. The thermal pads came apart when I removed the old transistors. You'd think the repair kit would have those with it. I guess it will be a learning experience one way or another. One of my philosophy professors once said "Sometimes knowledge makes a slow and bloody entrance".

[budm]

Re: Lg 50pg20 secondary fuse grounded to heat sinks

They do not come with the kit because they are re-usable unless they are damaged, same for the mounting screws & nuts,