Re: LG47LC7DF Fuse Blows
Questions: Is ESR important on Polypropylene capacitors as a means of deciding if they are good or not? What is considered a Low ESR for Polypropylene capacitors? The one Datasheet I could find that listed the ESR of a 1uf 400v Poly Cap said the ESR was 54 mohms and that these were low ESR caps. When dealing with Electrolytic caps this would be considered a high ESR.
When I test a poly cap pulled from the circuit board I am working on, it tests (with cap meter) at 6.3 ohms. That is a far cry from 54 mohms.
killian6pk
Badcaps Veteran
Last Activity: 01-11-2018, 11:51 AM
Joined: 04-19-2010
Location: Kentucky
-
Re: LG47LC7DF Fuse Blows
Ok thanks,
So could they be showing up in circuit as a shorted component? I was testing them out of circuit when they tested shorted. The reason I ask is that I saw a guy on youtube who was checking a tv power board for shorts by setting his dmm on diode mode and putting his leads on the ac power imput pins (no ac going into board) and he said if it had a reading there was a shorted component and if it read OL then there were no shorts. Does that make sense?Leave a comment:
-
Re: LG47LC7DF Fuse Blows
Ok thanks, what about the going up or down in ohms and watts?Leave a comment:
-
Re: LG47LC7DF Fuse Blows
I have attached a picture of 1 of 2 resistors that are shorted. They both show a dmm measurement of 0.3 ohms that fluctuates from 0 to 0.3 ohms. Doing a continuity check they measure shorted. When I look on a resistor calculator (like the one on digikey) they don't have a black stripe as a choice on either band 1 or 5. I think this is a 1 watt resistor due to it's size compared to others I have. What I am trying to figure out is what is it's true resistance so that I can replace these 2. Also if I can't find that resistance what can I replace it with. Can...Leave a comment:
-
Re: LG47LC7DF Fuse Blows
Thanks for the link that did help.
Leave a comment:
-
Re: LG47LC7DF Fuse Blows
I have done some other component checking. On the heat sink opposite the Bridge Rectifier there are two Power Mosfets Q607 and Q606 and one Diode. The diode reads OF one direction .387 the other is that likely a good or bad diode? The two mosfets test bad there are no readings in any direction I test the pins in. Source to Drain or Source to Gate so I will replace them. Let me know if the Diode needs to be replaced....Leave a comment:
-
Re: LG47LC7DF Fuse Blows
While I was waiting I pulled the Bridge Rectifier off of the board again to test it. In diode mode on dmm red lead on ac pin black lead on + reading of .489, Switch lead same two pins reading of OF. Red on other ac pin black on neg. pin reading of OF. Switch leads same two pins reading of .491. Am I correct in thinking the BR is good?Leave a comment:
-
Re: LG47LC7DF Fuse Blows
With the meter set on ohms and the board not plugged in the fuse reads OF. So the fuse did blow.Last edited by killian6pk; 12-06-2017, 11:48 AM.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
What I meant was that I put one probe on one end of the fuse and the other probe on the other end of the fuse. Was that not correct?Leave a comment:
-
Re: LG47LC7DF Fuse Blows
Well good news and bad. I installed the shorted mosfet and a couple of other suspect components and put the board back in and turned on the set. The main fuse did not blow and has 120v across it. The bad news is that there is another fuse near the two large caps and it does not have any voltage across it, but checks good. My guess is a bad bridge rectifier, does that sound likely? I tested the BR out of circuit first before doing anything else to the board and I thought it tested good, but I must have been wrong.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
see belowLast edited by killian6pk; 12-06-2017, 11:02 AM.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
I finally found a reference to this Diode. They say it is a Rectifier Diode, but still no data sheet. Don't know if that helps or not.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
I have found a diode (black with blue strip) numbers are S3V79 (9 has a line under it and next to nine is a blue dot) can't find datasheet anywhere (internet search, digikey or mouser). On meter diode check setting reads both ways in circuit. Took it out of circuit it reads only one way with OL when leads are switched. Is it likely to be ok? Board designation is a D so not a Zener.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
What about testing the surface mount resistors? Do I need to take them off the board?Last edited by killian6pk; 12-02-2017, 01:04 PM.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
How do you check surface mount resistors diode etc. Do they have to be removed from the board, or can they be read in circuit? Also I have a surface mount component with board identifier FB101, what does that stand for? It reads shorted with my dmm on continuity (both ways). There is no mention of it in the component list in the manual.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
Bud you asked me to check the components between the gate and the output drive pin of the smps IC attached is a link to that datasheet could you point out the output drive pin?...Leave a comment:
-
Re: LG47LC7DF Fuse Blows
On the InRush Current Limited (thermister) I can't get the actual part. It's specs are 6ohm 6amp 20%. I can get a 5ohm 6amp 25%. Would that work as a replacement.
Pulled a small Zener Diode from base of bad Mosfet. Readings are .670V and OL. I think that one is ok. Will keep looking for the other componets that Bud mentioned in post 31.Last edited by killian6pk; 11-26-2017, 11:33 AM.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
The picture of the back of the board shows a small IC labeled U301. That is the one that I think is the PFC IC.
Also picture of the cable voltages on the front of the board. Two pictures to make sure I got all three connectors where you could read them....Leave a comment:
-
Re: LG47LC7DF Fuse Blows
I have checked on Digikey and Mouser under that SFA0001 part number and neither one has that number. Will email digikey with that pdf file attached and see if they can find a comparable part. I'll wait until we verify that I need it.Leave a comment:
-
Re: LG47LC7DF Fuse Blows
I believe you found it. Thanks for hunting it down. Of course I am not smart enough to be able to understand any of that. Looks like it might be 6-16 volts in and 15 volts out. That is all I can tell. Will need help in getting specs to order if it proves to be bad after testing.Leave a comment:
No activity results to display
Leave a comment: