sharp 80" LC-80LE632U no power

[sputnikoff]

I have 80" sharp ith strange symptom its blowing diode 7200 a and b.I replaced and did same thing.I dont have diagram so its hit and miss with misses winning lol.It does the 2 short 2 long flashes of power light but no combination of button pressing changes that,because its power related.The power supply is a dsp-285bp.Any input would be great.

[budm]

Re: sharp 80" LC-80LE632U no power

For us to help we will need good clear pictures of the whole backside of the TV showing all the boards, and the straight shot pictures of the whole top and bottom side of the power supply board so we can read the printed texts on the board.
It is hard to do long distant troubleshooting without seeing what we are dealing with.
What is the history of the TV? Any works were done to the TV before?
The more details we get the better chance of finding the cause of the problem.

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

Here is power supply pic.A guy previously worked on it but did nothing. Apparently just too remove back cover and said it was out of his league.Seen replacement board on a couple of sites but its blowing diodes so something in general area causing problem.Bit hard without schematic.

[CapLeaker]

Re: sharp 80" LC-80LE632U no power

There is nothing much I can see on that picture like that. We need to be able to see the details. Also what diode is blowing? So you replaced the PSU and it blew again? How do you know it is blowing diodes? Did you replace them?

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

Yes replaced them and they shorted.here better pic.

[budwich]

Re: sharp 80" LC-80LE632U no power

You should probably start by looking at all the "three legged components" and checking them for short conditions ... mostly with reference to the middle leg.

then potentially, if you have more diodes (for repair / replacements) while testing, you can try disconnecting the cables going to the back lights and see if you get different results. Similarly at the tcon, try disconnecting tcon to panel cabling to see if those results differ. It might help isolate any sources of "more draw" than component spec.

[budm]

Re: sharp 80" LC-80LE632U no power

What resistance do you get when tested D700A and B off the board in Both direction?
What resistance do you get when check the resistance between the Cathode pad of D7200A and the negative leg of C7200B?
I have doubt that the diodes are bad due to the fact that there are bleeder resistors R7200A ~ D connected to the output of the rectifiers.
Pictures provided by shopjimmy, DELTA DPS-285BP A.
At this point you must report the DC Voltage readings of ALL 3 connectors on the cold side, you MUST put down the pin name and number and then follow by the Voltage reading for each pin so we can easily see what you have and what you do not have, failing to do so will make it hard for you to get help.

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

i removed d 7200 a and b shorted both ways.Im not sure about 3 connectors on cold side what your referring to?The cold side from what i can tell feeds power to hot via t7601.Then various levels of voltage sent to different sections.On left side seems run through those 4 diodes and then drives l1 and l2 connector.Those 16 transistors drive leds i would assume.

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

Also with respect to ground q7291 ,7288,7283 etc 3 of them don't read same with respect to ground. Most are around 5 megs but q7256 ,7260 and 7263 are 1.5 megs.

[dick_barton]

Re: sharp 80" LC-80LE632U no power

What were the original two diodes part number as written on them and what part number did you replace them with?

[budm]

Re: sharp 80" LC-80LE632U no power

i removed d 7200 a and b shorted both ways.Im not sure about 3 connectors on cold side what your referring to?The cold side from what i can tell feeds power to hot via t7601.Then various levels of voltage sent to different sections.On left side seems run through those 4 diodes and then drives l1 and l2 connector.Those 16 transistors drive leds i would assume.

So the diodes show <1 Ohms in both directions.
Those D7200A ~ B formed bridge rectifier circuit, so it does not look right to have just those same two diodes go out without the other 2 get damaged also.
My post #7 request:
"What resistance do you get when check the resistance between the Cathode pad of D7200A and the negative leg of C7200B?"

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

mur420g are diodes.The resistance .3ohm both directions.They were 200v 4a I only had 1000v 6a so i tried them.I like ur schematic budm.

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

With Connector L1 and L2 unplugged it doesnt blow diodes.Must be field shorted.

[budwich]

Re: sharp 80" LC-80LE632U no power

you can measuring some of those cable pins to see which are in trouble... maybe but i would have thought that there would be some shut down circuitry to prevent any overdraws. doing a led. replace on an 80 will be fun.

[CapLeaker]

Re: sharp 80" LC-80LE632U no power

mur420g are diodes.The resistance .3ohm both directions.They were 200v 4a I only had 1000v 6a so i tried them.I like ur schematic budm.

It's not only about the voltage and amp reading of the diode. It needs to be an ultrafast rectifier diode in this circuit. If you just put a regular recovery diode in there, it will pop.

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

ok i have em on order.The ones i used are pretty close in specs ,especially just for momentary test.

[budm]

Re: sharp 80" LC-80LE632U no power

"What resistance do you get when check the resistance between the Cathode pad of D7200A and the negative leg of C7200B?"
I still do not see the answer on this one, BTW with and without connector L1, L2.

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

Update 7200 b keeps shorting on power up,with l1 and l2 connected.The resistance between cat of d7200a and c7200 b was 3.7 k but with new diode is in megohm reading.

[budm]

Re: sharp 80" LC-80LE632U no power

https://www.badcaps.net/forum/attach...1&d=1523995536
Please measure the resistance between the two leg of R7200A.

[sputnikoff]

Re: sharp 80" LC-80LE632U no power

Update budm.I found 1 mur460 and not the required mur420 and tried it apparently diodes are CRITICAL to be 25 nanosecond.The unit fired up ok.I will have to wait for diodes to arrive.So bottom line diodes 7200a and b were gone causing 2 short and 2 long flashes on chevron power light in front.Thanks for help again budm.