Is this PSB still work saving???

[tvprobs]

Hello,

This power supply had a resistor burn up in it. I'm curious if it's worth trying to save as there is a hole in it. Still seems pretty usable, but i've never had one this bad. Fuse did not blow, and other parts around it seem to be in working order as well. Cleanup on this has been minimal so far as i just wanted to be able to post pictures first. Also, if this is worth saving could someone help me identify the resistor needed to throw in there. Board is and LG 2300KEG031A.

thank you

[budm]

Re: Is this PSB still work saving???

You need to remove the carbonized section.
I would also check the components on the output side of the resistor to see if anything is shorted out, it can also be due to cold solder joints on the resistor leg.
Can we see the pictures of the resistor?
Schematic:

[SLK001]

Re: Is this PSB still work saving???

If it's your board, I would try to save it. If it is a paying customer, I would get a new board.

Any insight on what cause the resistor to blow? It takes a lot of current to turn a resistor into a plasma jet that burns everything in its path.

[tvprobs]

Re: Is this PSB still work saving???

You need to remove the carbonized section.
I would also check the components on the output side of the resistor to see if anything is shorted out, it can also be due to cold solder joints on the resistor leg.
Can we see the pictures of the resistor?
Schematic:

Here's a picture of the resistor and the fuse. Somehow the fuse is still good, just got so hot that it "fused"(no pun intended) to the clip that was holding it on one side. I've checked other components in the circuit path and we seem to be ok. particularly the diodes (there are 3) immediately after the resistor before leading to other parts and they check out.

FYI. I'll likely keep this TV for now and replace the board altogether if i give it to someone i don't know. But if it's worth salvaging i would like to try to get it up and running.

[budm]

Re: Is this PSB still work saving???

Did you try measuring the resistance of that resistor? I think the problem was bad solder joints on the resistor legs.

[tvprobs]

Re: Is this PSB still work saving???

Did you try measuring the resistance of that resistor? I think the problem was bad solder joints on the resistor legs.

I measured and got 4.3K Ohm. Would that be pretty accurate even when it's burned up like that? Also, when replacing it should i use a different type of resistor. Looks like it should be a carbon film. Would there be benefit to changing to a different type or just get the same kind?

Thanks for your input by the way. It's extremely appreciated

[budm]

Re: Is this PSB still work saving???

Did you look at the schematics/ I gave you the link to download.

[R_J]

Re: Is this PSB still work saving???

I don't think the resistor is on the schematic, The shopjimmy picture seems to show a 1.21MΩ 5% But that does'nt seem correct? I believe it is a a 120Ω, You shuld also check D130,D131,D101,D101a,D101b

[tvprobs]

Re: Is this PSB still work saving???

I don't think the resistor is on the schematic, The shopjimmy picture seems to show a 1.21MΩ 5% But that does'nt seem correct? I believe it is a a 120Ω, You shuld also check D130,D131,D101,D101a,D101b

FYI: Using the Shop Jimmy PHOTO!!!!

All diodes you listed seem to check out.

I tested the resistors R2 and R3 as they seem to match the resistor in the photo. They measured at 120 Ohm.

Also, I found U101 had a pin that was burned up. Following the trace of the burned pin, i found D106A appears to be bad and possibly the resistor at R101 is only giving a reading of 1.6 Ohms. I'll pull them out of circuit when i get time. However, I think this board has promise to be resurrected and it may just be swapping some components and re-soldering some joints throughout the board.

[Diah]

Re: Is this PSB still work saving???

this is remind me on CRT TVs before we face the hot area on PWB section catch fire. we used to replace and re connect any hole on boards and they worked. but this an important to replace most ceramic cap on the area.

[tvprobs]

Re: Is this PSB still work saving???

Did you look at the schematics/ I gave you the link to download.

So i pulled a few components that i suspected bad from the blown resistor all the way up to the IC labeled U101. Judging from the schematic R101 tests well at 4.7K Ohm. However, the diode D106A shows open either way i test it. It seems to have failed causing the burn up of the IC on the pin 7 Drain. I'm looking to replace this diode but can't seem to find anything online when i look up T2D89. Not sure what i should sub in for it. Any help there would be awesome. Once the IC, Diode, and Resistor are in place i think i can at least try to plug in the board.

[R_J]

Re: Is this PSB still work saving???

The diode is likely good, it would be a tvs/zener diode and will check open, similar to the P6KE series

[tvprobs]

Re: Is this PSB still work saving???

The diode is likely good, it would be a tvs/zener diode and will check open, similar to the P6KE series

Ok, i'll have to do some research on TVS diodes. That one stumped me. Any idea what may have caused that drain pin to burn up? When i pulled the IC out the pin just came right off. Or should i look to just get power up and going on the board and see what happens? I uploaded the schematic that Bud found.

[budm]

Re: Is this PSB still work saving???

can we see the U101 that has the pin burn up and good clear picture of that section?
And good clear straight shot of the whole top and bottom side of the board?

[tvprobs]

Re: Is this PSB still work saving???

can we see the U101 that has the pin burn up and good clear picture of that section?
And good clear straight shot of the whole top and bottom side of the board?

Here are the pictures. I uploaded 2 from shop jimmy as it is the same board and shows all components in place.

I also have the IC FSQ510 showing the pin missing where it burnt up. There are also pictures of my board front and back. Not was well lit, but i can get better lit ones if needed.

[R_J]

Re: Is this PSB still work saving???

It's likely the ic just shorted (power spike maybe) and burnt, the only other protection was the R101A resistor which also burnt. I would also change C104 as that standby circuit runs all the time.

[tvprobs]

Re: Is this PSB still work saving???

It's likely the ic just shorted (power spike maybe) and burnt, the only other protection was the R101A resistor which also burnt. I would also change C104 as that standby circuit runs all the time.

Thank you. just one last question. What's the best type of resistor for that R101A spot for longevity? Obviously there's a lot of voltage running through there and i want to be sure it's going to hold up. Is there benefit to a metal film vs. a carbon film?

[R_J]

Re: Is this PSB still work saving???

Remember it is acting like a fuse so you want it to open when required, either should be ok, metal film flame proof would work ok

[tvtimmy]

Re: Is this PSB still work saving???

When the fsq510 goes bad it will smoke the resistor everytime, especially when a bigger fuse is inserted. Replace the FSQ510, the resistor(I use 1 watt), the fuse with the holder resoldered in, and touch up all the transformer mounting pins and all things screwed to heatsinks, and it should be fixed.

[tvprobs]

Re: Is this PSB still work saving???

This is why i love this site. The details bring it all together for people like me trying to learn beyond the big picture of it. I've got the parts ordered and should have them early next week. Slowly stocking extras as i go for future use. I'll check back regularly in case there's any additional input or concerns that we haven't discussed.