Samsung Syncmaster T220 blown green fuse F301

[sinip]

I replaced some capacitors in this one a long time ago, and it was working OK until it again developed a "slow start" in cold weather, especially. Once it started, all would be well.

So, while it was trying to start, I've heard something getting fried inside, and after opening it, I found 4A green fuse F301 blown. Now, I'm measuring short across the C301 capacitor (1000uF/35V, it is good itself, of course).
MOSFETs in the inverter are STM8139 (U302 and U303) and have no visual sign of being burnt. I don't see anything else burnt, either.

Now, I downloaded several service manuals, and none of them has the inverter schematic?!?

If anyone has the schematic of the inverter, that would help. Otherwise, any advice at this point would help as well.

[SMDFlea]

Re: Samsung Syncmaster T220 blown green fuse F301

If anyone has the schematic of the inverter, that would help. Otherwise, any advice at this point would help as well.

Post all the PCB board part numbers,and some pictures.

.

[sinip]

Re: Samsung Syncmaster T220 blown green fuse F301

OK, here they are...

Thanks.

[R_J]

Re: Samsung Syncmaster T220 blown green fuse F301

U202 or U203 is likely shorted. The two small electrolytics (C120,C123) near U101 are likely bad causing the slow start

[sinip]

Re: Samsung Syncmaster T220 blown green fuse F301

Thanks.

You mean U302 or U303? Which, again, could point to a bad CCFL?

[R_J]

Re: Samsung Syncmaster T220 blown green fuse F301

It is unlikely a bad ccfl, It might be a bad (T301) transformer, or it may have been the slow startup that caused the voltage to the inverter section to be bad and mosfet just shorted.

[sinip]

Re: Samsung Syncmaster T220 blown green fuse F301

Thanks, yep, I desoldered those two MOSFETs, and resistance is back to normal across C301.

I'll check those caps as soon as I find my ESR meter. But no hurry since I have to order MOSFETs from Aliexpress. I also await the arrival of the CCFL tester I ordered several weeks ago, so I'll be able to check everything.

[R_J]

Re: Samsung Syncmaster T220 blown green fuse F301

Just replace the two caps I mentioned, the esr/cap checker will not test them under actual working condition. They are cheap. The ccfl's will not cause a problem with the power supply, if the ccfl are bad or broken, they won't light, if they are weak the screen may be slightly red and dark.

[sinip]

Re: Samsung Syncmaster T220 blown green fuse F301

However, on the second look...

The resistance across C301 is still kind of low - 27 Ohms or so, and that cap is across ground and pin 13 - Vin of the FAN7317 chip, which is an actual inverter and Fairchild's PDF file has a typical application circuit of the inverter, including MOSFETs, transformers and all.

So, I wonder now, in the absence of another FAN7317 for comparison, whether it is fried too?

[R_J]

Re: Samsung Syncmaster T220 blown green fuse F301

Max Vin voltage is +24v, I suspect the FAN7317 drive ic is likely bad. I have an inverter with a FAN7314 and the Vin is very high resistance, I suspect 27Ω is too low

[sinip]

Re: Samsung Syncmaster T220 blown green fuse F301

Thanks for the confirmation. I've lifted pin 13 from the PCB, and indeed FAN7314 has 27 Ohms between Vin and GND.

So, another thing to order and wait a bit. Ah well.