Re: 820-01958 MBA 13" '20 A2179 Schematics/bv request
Thank you so much!
Markpixley
Member
Last Activity: 08-10-2022, 03:11 PM
Joined: 08-11-2012
Location: Williams
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Re: Sharp LC-40LE550U no backlight
That seems to be the one common place all the traces in question land at...I will see if I can source one and replace it...I think Digikey handles richtek stuff......Leave a comment:
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Re: Sharp LC-40LE550U no backlight
Yes very bright and distinct picture...something a little weird though (could be related to a mad mojo connection I was using to short pin 13) was any time the volume went up loud the screen would dim...mind you the back is off and things are not all connected solidly, but it might be related to a power draw...
Other than that the screen looked really good but changing the backlight in the menu did nothing...+/- had no affect......Leave a comment:
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Re: Sharp LC-40LE550U no backlight
This looks identical to my TV (which I picked up for $25.00 on CL) but mine is a Sharp...rebranded ...China will get our money one way or another......Leave a comment:
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Re: Sharp LC-40LE550U no backlight
So wait...help me understand...if I have 340 volts does that mean its 8 volts to low and I have an open in the LED string still?
By shorting to ground am I simply by-passing the open short somewhere?Leave a comment:
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Re: Sharp LC-40LE550U no backlight
I'm wrong if you are looking down on transistor the way the data sheet shows the cathode would be pin 3...which is where I get 2.45v
Pin 1 I get 4.34v (if pin is grd ref)...Leave a comment:
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Re: Sharp LC-40LE550U no backlight
Yes 340.8...I had the same issue with the LED solder strip but I'm fairly certain it is fixed....just for testing last night I shorted pin 13 to ground popped a USB stick in with a movie and watched a little to see what it would do...the back light seems on full with no option to change it (remote changes nothing)...my point is the screen looks to be full back light so I'm fairly sure the connection issue with the light strings is gone...but what do I know?...Leave a comment:
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Re: Sharp LC-40LE550U no backlight
Testing the negative of C115 and pin 1 I get 2.45......Leave a comment:
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Re: Sharp LC-40LE550U no backlight
By the way thanks for your input...I am learning...slow to process this stuff though...I appreciate your advice.Leave a comment:
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Re: Sharp LC-40LE550U no backlight
Ok upon closer inspection I am wrong...the last part of that resistor chain does not go "end to end"...the 332k ties into the top end of the 1204 (1.2Mohm) but then the trace swings around it and connects to the bottom end of the 390k which goes on to the top of itself to the 10k>>>to the cap .756nf...
A continuity test between the bottom end of the 1.2M and the top of the 390k indicates they ARE connected...so they are connected in parallel...and their end point goes on to the 10k...Leave a comment:
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Re: Sharp LC-40LE550U no backlight
ok from what I can tell...the positive lead of the cap goes to that string of resistors...
Starts with "3323" (332KoHms)>>>3323>>>3323>>>1204 (1.2MoHms)>>>3903 (390k)...
then it goes to a 1002 (10k) and splits into a trace that looks simply like a test point (no connection to anything) and the other side to a smd cap that measures .756nF>>>then into the far right leg of the UL1032 (looks to be an AS431)...which if I am correct is the cathode leg of a shunt regulator......Leave a comment:
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Re: Sharp LC-40LE550U no backlight
Thanks budm, I will try to follow the (+) side and see how it lands, it goes through a string of resistors that seem to be in parallel with the outputs CN202/203...the RL series (about 5 immediate) on the far bottom left side of img.3...they all seem to head to UL103 a transistor...I'll see if I can get values tommorow......Leave a comment:
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Re: Sharp LC-40LE550U no backlight
ok the second possible path is through three resistors all marked "O" smd...measuring .3 Ohms each then into a smd capacitor with no marking but measuring .182 nFLeave a comment:
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Re: Sharp LC-40LE550U no backlight
The first resistor FB hits is a 4703 smd that measures 470k out of circuit......Leave a comment:
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Re: Sharp LC-40LE550U no backlight
Pins 8,9,10,11, and 14 all connect and join up to the (-) of the large 450v47uF capacitor...Leave a comment:
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Re: Sharp LC-40LE550U no backlight
Well my quickest reply is the back light does NOT come on when shorting 13>>>12
ONLY when shorting 12>>>Ground or 13>>>ground...makes no difference which one...
9/10 are soldered to the ground plane they have no other connection they are all connected to the ground pin (8) on the same plane...I am pretty sure after inspecting this board it is only using outputs 13/12...
My voltage readings on the Cn202/203...
340>>>drops to 339
287>>>>drops...Leave a comment:
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Re: Sharp LC-40LE550U no backlight
So this is where I am at...the FB pin (1) was getting 12.28 volts...waaay to much as far as I can tell...by jumping pins 13/12 to ground it dropped the voltage on FB to 1.9 which is below the high tolerance set (3.3) basically I forceed the FB to low and everything works...now I need to figure out if it is the UD101 or the circuit from the FB pin ...Leave a comment:
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Re: Sharp LC-40LE550U no backlight
So further testing...
By jumping pins 13>>>10 and 12>>>9 o the UD101 I was able to get the backlight to light up...
I have 13.58 volt on 13/12 and none on 9/10
9/10 are not connected to anything except ground, so basically forcing 13/12 to ground turns on the back light...Last edited by Markpixley; 09-18-2016, 07:25 PM.Leave a comment:
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Re: Sharp LC-40LE550U no backlight
P/N for UD101 is RT8300
[url]http://www.richtek.com/en/Products/LED%20Driver/DC_DC%20Lighting%20LED%20Driver/RT8300[/url]Re: Sharp LC-40LE550U no backlight<b...r/RT8300[/url]...Leave a comment:
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Re: Sharp LC-40LE550U no backlight
Thanks, budm, so now that I think about it, he had 3 volts there PRIOR to finding his short and his was off? I have <3v which means it is on...?
Or am I backwards?
I get what you mean about the supply voltage but is it possible that the ricoh chip (UD101) drops the current when it find a led fault/short/open to below "strike" threshold for the lamps? (I know thats not what happens here but its the basic idea)
"On most sets, BL_ON (backlight on) going high (> 3) means...Leave a comment:
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