What would cause this fuse to be blown on this inverter?

[mockingbird]

I've got a Panasonic TC-20LA2 I got a while back... The symptom is that there's absolutely no display, not even a non-backlit display when I check with a flashlight. Changing the video inputs does not help.

I opened it up, but can't find anything obvious. I want to check the voltages going from the logic board to the inverter, but I can't find any reference in the service manual as to what to compare them to.



If you look at the red arrow, it points to a fuse labeled "100AC 5A". There are three of them on the inverter. That particular one is reading (infinite?) very high resistance. The other ones test fine.

Attached is the service manual and a higher res photo.

Anyone have any tips where I can order one online for a few bucks rather than having to pay digikey 8 bucks to ship it?

[R_J]

Re: What would cause this fuse to be blown on this inverter?

Check those 8 pin ic's close to the fuse, one of them may be shorted. compare the reading from one of the other ic's on the board

[budm]

Re: What would cause this fuse to be blown on this inverter?

Those are Dual MOSFETs, I believe they are SP8M8.
Check for shorted Source to Drain.

[mockingbird]

Re: What would cause this fuse to be blown on this inverter?

Check those 8 pin ic's close to the fuse, one of them may be shorted. compare the reading from one of the other ic's on the board

Those are Dual MOSFETs, I believe they are SP8M8.
Check for shorted Source to Drain.

Geniuses!



Pins 3 and 4 on the circled MOSFET are shorted.

All other MOSFETS test fine. Do you think the FET is the original cause or something that was taken out by something else, for example a dying CCFL tube?

[tom66]

Re: What would cause this fuse to be blown on this inverter?

Most likely just the fet... it happens.

[budm]

Re: What would cause this fuse to be blown on this inverter?

I fixed a couple of this models due to blown MOSFETs, as you can see, they do not have much copper plane to act as the heatsink.

[mockingbird]

Re: What would cause this fuse to be blown on this inverter?

What did you use to replace SP8M8? I can't find them anywhere?

I can find equivalent's but with different "Vgs(th) (Max) @ Id". I assume that I can use parts with higher maximum voltages and amperage as long as the resistance is the same or lower. But can I use something with a slightly different gate voltage, considering that the SP8M8 is between 1 and 2.5 volts?

Also, did any of those tiny diode packs or resistors need changing as well?

[tom66]

Re: What would cause this fuse to be blown on this inverter?

You don't usually need to be worried about VgsTH as it's so variable (there, alone, it has a 250% tolerance -- most basic semiconductor properties are not well controlled.) Instead, compare RdsON vs Vgs; if the current device has x.x ohm at x.xV Vgs, you need to meet or go lower than that.

[budm]

Re: What would cause this fuse to be blown on this inverter?

http://www.aliexpress.com/store/prod...598207795.html

[mockingbird]

Re: What would cause this fuse to be blown on this inverter?

Thanks.

I ended up using the Fairchild SI4542DY and a Littlefuse 451 series fuse.

Great little set. Had to go through a few universal remotes before I could find one that had the "enter" key working for the menu.