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-   -   SHARP LC-80LE633U has open resistor r7133 on PSU (https://www.badcaps.net/forum/showthread.php?t=76450)

triplefour 05-05-2019 03:52 PM

SHARP LC-80LE633U has open resistor r7133 on PSU
 
2 Attachment(s)
SHARP
LC-80LE633U
huge 80" tv that needs 2 people to move around.
got from a friend
it was his friends tv
he said they were watching it and heard a pop
then it wouldnt turn on again.

checked voltages on psu.
high voltage present.
pfc standby voltage ~175vdc on all 4 caps so seems ok.
no voltage on cold side.
no 5vsb.
measured voltage on components to see where it is and where it isnt.
found resistor R7133 to have 175v going into it but nothing coming out.
found resistor R7133 to be open.
removed, and found small hole in it.
resistor code: red red gold gold
according to the app on my phone
it means 2.2 ohms +- 5%
what resistor should i replace it with so this doesnt happen again?
should i go with a higher ohm resistor? and what about watts? does the color code tell you anything about how many watts it can handle? do i have to use ohms law?

R_J 05-05-2019 04:54 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
If the resistor is open, and you don't have standby 5 volts, ic7102 will be shorted, check the resistance of the internal fet, pins 6 to 8
Replace it with 2.2Ω 1/2 watt flame proof, replace the ic also

budm 05-05-2019 05:21 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
Quote:

Originally Posted by r_j (Post 895023)
if the resistor is open, and you don't have standby 5 volts, ic7102 will be shorted, check the resistance of the internal fet, pins 6 to 8
replace it with 2.2Ω 1/2 watt flame proof, replace the ic also

+1.

petehall347 05-05-2019 05:30 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
replace with wire and look for smoke ..... ONLY joking but its how i read things sometimes . follow the good advice above . fuses dont pop for no reason unless really old but thats another story . oops meant resistor .pretty much same thing in some cases .

triplefour 05-05-2019 10:28 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
thank you for the replies. i am really trying to learn how to think about these problems so if you wouldnt mind telling me how you know that the IC7102 would be shorted as well? i can guess that "a resistor wont explode for no reason" , and that there is only 1 IC controlling things on the hot side...but how do you know what the IC is and exactly which pins to check? are these that common or have you worked on this tv before?

and also where should i buy the resistor from?
i see these on ebay, but it doesnt say anything about flame proof and i get no results when i add that to the search.

https://www.ebay.com/itm/10-x-2-2-Oh...frcectupt=true

im not near the board at the moment so i will have to test that IC later tonight, and hopefully be able to read the markings, and hopefully be able to find the replacement

budm 05-05-2019 11:06 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
Sharp RUNTKA903WJN1 Power Supply / LED Board
https://www.shopjimmy.com/sharp-runt...upply-unit.htm

If you trace out the circuit to see how the resistor R7133 is connected, you will know that resistor is used as the fuse to feed the DC V to run the SMPS IC7102, the you look up the spec sheet of that IC to locate which pin is the Source pin and the Drin pin of the internal power MOSFET which drive the power transformer T7101, you can also look at the application circuit that is usually provided in the IC spec sheet.

triplefour 05-06-2019 04:23 AM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
1 Attachment(s)
ok i did some tracing as best as i can, but i really cant see how you guys do it just from the pictures. it gets so muddy there close to the IC7102 pins, i just cant tell whats connected to what. i cant see how r7133 connects to pin 6 or 8

and i cant figure out what is "driving" T7101
it looks like:
pin 1 would be getting 175v if the resistor R7133 was not blown
pin 2 is not connected to anything
pin 3 would also get the 175v from R7133 but there is a diode opposing that flow.
pin 3 also appears connected to pin4 of IC7102, so could be getting some signal from there. i admit im foggy on how a power transformer is "driven" in the first place.
pin 4 and 5 are connected to each other and nothing else, so i assume they just arent used.
pin 6 i have a real hard time telling what is going on there. i cant be sure if it traces back to a pin on the IC or not.
pin 7 is connected to a diode which shouldnt be letting any current in

maybe i would be having more luck if i had the board in front of me, but i really want to learn how you guys know stuff just from looking at these pictures!

please tell me if ive made some mistake in tracing this, or thinking about it.
thank you

also i still am wondering where to get the correct replacement resistor. is there another term besides "flame proof" i should be searching for?

R_J 05-06-2019 08:38 AM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
You traced it properly, The voltage comes from the trace with the resistor and connects to pin 1 of T7101, then comes out of pin 3 and connects to the ic.
On the primary side of T7101, Pins 1 & 3 are the primary winding, pins 6 & 7 are a secondary winding used to supply the run vcc for the ic.
What is the number on the ic as you will need to replace it?

Here is the digikey url https://www.digikey.com/products/en/...=1&pageSize=25
PPC2.2BCT-ND would work

triplefour 05-06-2019 04:12 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
3 Attachment(s)
thanks RJ but i dont think i traced it as well as i could have. ive added arrows along the lines to show what i think to be the direction of the flow.
also i added a line to show that it connects to pin 1 of T7101.
also i added a marking showing the direction of the diode D7112.
i am confused about this diode, because it would seem to allow current to flow from pin 3 of the transformer back to the resistor. am i missing something here?
also curious about this diode because it appears to be shorted. i get low resistance (meter beeps) both ways.
what would be the purpose of allowing current to flow back the way it came?
it makes no sense to me...probably because im thinking about it all wrong?


another thing i may have done wrong:
i traced it going through a line of 4 smd resistors all marked 1004 (R7124-R7127) which i have now checked with my meter and found no continuity and looked up the smd code which comes out to 1 Megaohm. strange my meter should be able to show up to 2 Megaohm but it still shows OL
can someone tell me what this line of resistors is for? it seems like it would block all current.


also i am not clear on how we know for sure the IC is fried and needs to be replaced. as for checking the resistance between pins 6 and 8 as you said, i get no resistance, but that makes sense because it looks like all 4 of the pins on that side are connected to the same plane.

maybe a clear picture of this IC will shed some light
IC7102:
1133
TNY274PN
949150



thank you for being patient with my noobery

i will be reading this datasheet and poking around some more

thanks for the link. ive got 5 of those resistors and the IC in my cart but i think im gonna need to replace that diode as well?

R_J 05-06-2019 04:31 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
The resistors are likely ok, they can be hard to check in circuit, they are just to supply a small voltage for the sense pin of the ic for under votage detection.
The BEEP from a meter is usless info, to check the diode use diode test and report the reading (which is the voltage drop) ie .7xx for silicon or schottkey could be .3xx or .2xx
In your case the diode is across the primary winding of the transformer (snubber diode) and will only read a few ohms or even a short.

As for the ic, check the resistance between pin 4 [Drain] and any of the 5,6,7,8 [source] pins I suspect it is shorted
I did'nt know the ic number so I guessed, thats why I said pins6/8. Some similar ic's have the D at pin8 and S at pin6

triplefour 05-06-2019 04:38 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
thanks for clarifying about those 1004 resistors.

about the diode: yes i just realized this after i made the post. i lifted one of the legs of the diode to check it and it shows OL both ways (meter in diode check mode) but i see why in circuit it was reading as short. its connected to pin 1 and 3 of the transformer which is basically just a coil of wire, right?

but should the diode be reading OL both ways?
diode says T3D1D but the last D has a underline under it

really dont see what the purpose of this diode is anyway...seems like it would run fine without it?


im not reading any shorts between pin 4 and any of 5,6,7,or 8
i have to put the meter all the way up to 2m scale and i read 1.5mega ohm.
all other scales show OL
in diode check mode if i put black probe on pin 4 and red to 5,6,7,8 i get 0.4 voltage drop
if i reverse the probes, putting red probe on pin 4, i get OL for all 4 of those pins.

R_J 05-06-2019 04:51 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
The diode in this case is likely a P6KE150AAMP "TRANS VOLTAGE SUPPRESSOR DIODE" basically a zener and a regular diode connected at the cathode, It will read OL or open
If you are not reading a short on the ic it might be good but I doubt it. thats usually the only part that will blow the resistor, but if you order the resistor, get a few, you can replace the resistor and if the standby circuit works you are ok, if it blows again its likely due to the ic.

triplefour 05-06-2019 04:56 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
ok so dont worry about that diode... whats it for tho?
and also what do you think about my readings on the IC pins? how can i be sure if its shorted or not? should i just order the resistors and IC, and just try replace the resistor first, and see if it doesnt solve the problem?

the IC is only 1.50 and i bet id end up using it someday if not now

R_J 05-06-2019 05:02 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
The TVS diode is there to suppress any high voltage spikes, when ever you switch the Dc voltage through a coil/transformer (which is what the ic is doing) it will also generate large spikes of voltage (thousand volt spikes are possible) this would kill the ic eventually. so they suppress the spikes with this tvs diode

triplefour 05-06-2019 05:08 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
ok definitely put it back in then ;)
thank you for taking time to explain
i guess im gonna go ahead and order these parts unless you can think of something else i should check first?
is my idea of just trying to replace the resistor first a good one, or is there some reason i should definitely replace both at the same time? i dont mind if all that happens is i lose a 44 cent resistor if it could mean a chance at not having to replace the IC. thats why im ordering 5

i would be willing to spend more than 44 cents for the resistor. as i alluded to in one of my earlier posts, i'd like the idea of putting in a stronger part so that this wouldnt have any chance of happening again. any thoughts on that?

i mean just from a marketing perspective, wouldnt that be an awesome thing to tell the client whos tv you just repaired that its "better than new" now?

R_J 05-06-2019 05:23 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
The resistor is there to act as a fuse, too high a wattage would not be a good idea, maybe 1 watt. It would be like repacing a 1 amp fuse with a 10 amp, It will last longer but won't protect the same.
As for the ic, the internal fet may have shorted, then blew its junction open, or the control circuit inside the ic is damaged and kept the fet turned on instead of switching, who knows for sure.

triplefour 05-06-2019 05:25 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
i definitely dont. but you seem to be sure at least that the IC is toast :D am i crazy for having hope it isnt?

i guess what im wondering is, if i am correct about how the current is flowing, ive been looking at what is happening AFTER the blown resistor. could something have happened if we trace from the resistor back to the AC mains, could something have happened in there (before the resistor) to cause a spike that just blew this resistor and left everything else unharmed?

R_J 05-06-2019 05:47 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
Yes a spike may have caused it, jump in your time machine and go find out :) Usually when a part like this goes its caused by over current at the destination, not from the source. Replacing the resistor will tell you one way or another

petehall347 05-06-2019 06:01 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
look for shorts to ground after burned resistor . once you think you found the suspect remove it and check for short again to see if its gone yet .

budm 05-06-2019 06:29 PM

Re: SHARP LC-80LE633U has open resistor r7133 on PSU
 
BTW, you can test that snubber diode T3D1D with the LED tester if you have one since it can put out over 200V.


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