atec 37 inch lcd psu faulty?

[clean-machines]

i love getting into component level i got this tv the other day it shows an orange light upon putting ac mains into the psu,
the standby 5 volts is there and sends out to the main board but im only getting 1.44 volts back from the mainboard to turn on the psu.

thought it must be being dragged down and sure enough if you remove the 5 volt logic between main board and psu the psu on signal from main board is a steady 4.98 volts ? this is pointing me toward the psu faulty

also its making a funny quiet squealing noise sounds about 13khz (maybe well off) but its not stable you can hear variations in the audio squeal which makes me think its caput

i think iv done the obvious (not great on switch mode) checked the rectifier transistors all check ok only thing i didnt check was the

[clean-machines]

Re: atec 37 inch lcd psu faulty?

pwm controller anyone got a manual for this ? how does the 5 volts from the main board switch on the psu on this one? im not with the psu right now but i will take a look later on , cheers any help apreciated

[tom66]

Re: atec 37 inch lcd psu faulty?

Post a picture of your main board. I've repaired the 42" version of this.

[clean-machines]

Re: atec 37 inch lcd psu faulty?

hi tom i will do that as soon as i read your post its the same excat board as far as i can see il try upload them tomoro if i can work out how lol

[clean-machines]

Re: atec 37 inch lcd psu faulty?

here we go then heres some piccys

[URL="http://*************/photo/my-images/232/06072012361.jpg/"]
[URL="http://*************/photo/my-images/689/06072012360.jpg/"][URL="http://*************/photo/my-images/820/06072012359.jpg/"]
ics are 7601 628 , top middle of pic , loc ic12
13002L 604 top left of pic , LOC IC2
290g12 bottom right of pic loc , ic4

ok so the 7601 is a fairchild fan7601 green currentmode pulse width modulation contoller
the 13002L havent a clue what this is ???
the 290 g12 looks like a ritchtek RT8290GSP dc-dc step down converter (adjustable)
right so iv got 5 volts coming out of stb-5v and 4.98 v coming back in on the motherboard however this is open circuit to the psu ,
as soon as i put that steady 5 volts back onto the psu it drops to 1.48v?
also there is a squealing noise audible not mains ac much quicker just within the audible range and it sounds slightly unsteady ?
any help?

[tom66]

Re: atec 37 inch lcd psu faulty?

Sorry, not my power supply. Mine was different. What is the model of your TV?

13002 is an NPN power transistor - rare to see one of those on a TV power supply, ancient technology!

I would replace the 5V cap. It could fail without bulging.

[budm]

Re: atec 37 inch lcd psu faulty?

That 1.44V reading may be fine due to the voltage dividing of the pull up resistor on the main board and the Base resistor plus Vbe of the transistor.
Since this power supply has PFC circuits, you should check the DC voltage on th at main DC filter cap (the 450V cap), when the TV is off, it should have about 325VDC (230V x 1.414 = 235), and when the it receives PS_ON, the voltage should go up to around 400VDC, if it does then, that 1.44V is enough to turn on the transistor on the power supply board.
See example of the PS_ON receiving side on the power supply board.

[clean-machines]

Re: atec 37 inch lcd psu faulty?

thanks budm and tom , clearly i need to go back to school!

il check that is actually recieveing the signal by checking the dc filter cap

also tom i cant find a 5v cap could you point me in the direction, i esr`d most of the caps but il esr all of them on monday and get back , cheers

[tom66]

Re: atec 37 inch lcd psu faulty?

thanks budm and tom , clearly i need to go back to school!

il check that is actually recieveing the signal by checking the dc filter cap

also tom i cant find a 5v cap could you point me in the direction, i esr`d most of the caps but il esr all of them on monday and get back , cheers

It'll connect through a diode to the standby transformer.

[budm]

Re: atec 37 inch lcd psu faulty?

Did any one work on this board before? I can see the circuits areound the 12/24V power supply primary side has a lot of flux around the two MOSFET's.
By the way, we do need higher resolution pictures so we can easily zoom in and look at the details, pitures of the connectors taht we can read the labels will help also.

[clean-machines]

Re: atec 37 inch lcd psu faulty?

my uncle said the board was repaired 1 year ago and failed again after 1 year so he brught a new tv
so on posting pics i posted these 9 megapixels on a site , how are you putting them as thumbnails onto the thread?
never been on a thread before sorry guys , i assume they will be better quality as the hosting site has resized them even tho i told them not to ?

iv also done some soler re work myself on dry looking joints and i put the jumper in looks like the repair guy last time did the easy bit (replaced bad caps and replaced a large transistor and the smaller drive transistor as i guess that must have blew along with the larger one

right so il do those checks and il try uploading some better pics

http://*************/photo/my-images/207/dscf0182i.jpg/

http://*************/photo/my-images/43/dscf0183p.jpg/

these are a bit better sorry about the flash guys its nearly time to stop feeding the mugwai i think

[tom66]

Re: atec 37 inch lcd psu faulty?

When uploading your pics resize them to 2000x2000 or smaller and under 1.8MB.

[retiredcaps]

Re: atec 37 inch lcd psu faulty?

so on posting pics i posted these 9 megapixels on a site , how are you putting them as thumbnails onto the thread?

For the 9 megapixel, see

https://www.badcaps.net/forum/showthread.php?t=19629

Follow the instructions in my sig file exactly.

[budm]

Re: atec 37 inch lcd psu faulty?

I down load those pictures from your link, and they came out as less than 100K size.

[clean-machines]

Re: atec 37 inch lcd psu faulty?

okey dokey this is honestly the first time iv ever up loaded a picture onto a hosting web site
somebody better slap me into the year 2012 !

il report back on monday evening thanks again for your help

[selldoor]

Re: atec 37 inch lcd psu faulty?

Currently on vacation but thought Id just redo the pics and test the the uploading.- back late next week.
I'd resolder a few joints.

[clean-machines]

Re: atec 37 inch lcd psu faulty?

thanks guys il make sure they are no more than 2000x2000or under
quick update had a quick look last night dont have my scope at the mo just a multimeter ! just had the psu board on the kitchen table after making a bit of toast mmm,
powered it up and gave it a small pulse on the ps on tab to try switch it on, i heard a change in note of the buzzing , got slightly slower ,

it looks like the ic12 fairchild green current mode pwm controller is pulsing ok for the standby transformer,
however the chip on top left (the one that has a part number of the old transistor) loc ic 2 with number 13002 (8pin ic sm) seems to die,,,
ok so when the psu is not recieving ps on (standby mode) this illusive chip seems to have an 8 volt supply between two legs and 5.5 on another when i give it the on command this chip seems to die the 8 volts dissapear there is no output , but if im honest im not entirely sure how this setup works the ic 2 seems to do someting with a IR21571 chip ballast control chip iv also tested this and it seems that vdc pin 1 on this chip also dies i think it had 7 or 8 volts and when i sent ps on signal it dies to 0.3 volts
i know this board is worth nothing its an old tv with no hdmi input but come on if i dont find out why this thing aint working i wont be able to sleep at night ,,, yeah im one of those .
so on monday i will re work the entire board for solder to make sure and esr all the smaller caps like tom said il see if i find anything , thanks again

[tom66]

Re: atec 37 inch lcd psu faulty?

Does 5VSTBY stay stable when PS is plugged into main board?

[clean-machines]

Re: atec 37 inch lcd psu faulty?

well when ps is fully plugged into main board if i probe 5v stanby i get 5 v to the main board an orange standby light and 1.48v on pson however if i remove the ps on cable i get 5v from mainboard but budm explained this to me its a normal voltaged drop

tom should i be able to power up the psu on its own using ps on? iv tried and i get nothing from any outputs

[clean-machines]

Re: atec 37 inch lcd psu faulty?

budm

as the ps on goes high there is no change on the dc filter cap its 327v
and goes up (twitchy) to 328v when ps on is activated something is happening tho as you can hear it the tone changes
also tried tricking the opto isolators to switch it on and does the same thing so im sure it is TRYING to turn on when ps on is recieved by the ps?
i think the ic 2 is a current mode power factor control so il have to re test that but i think its not a problem it should still work if this is faulty right as all it does is reduce harmonics in the supply? or am i wrong? i usually am

could i ask what purpose does the large 16 pin ic have its a ir21571 saw a datasheet on it its a ballast control ic are they using it as part of the power supply or is it for the lighting ballasts?
i wouldnt think so as there is just a plain 24 volt out on the psu to the ccfl ballasts (one on the right and one on the left)
im at a bit of a dead end now might try replacing the ir2157 as according to the datasheet it has a lot of failure shutdown detection built in ?
this board will work again even if i have to replace every component untill it works at least then we`l know what it was i might even get another scope (mine is rubbish) cheap monotone 12mgz scope it brings me back to playing a gameboy trying to ge the angle just right so you can get half a decent contrast in the display

cheers again guys any ideas?