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]

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]

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

[clean-machines]

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]

here we go then heres some piccys

[URL="http://imageshack.us/photo/my-images/232/06072012361.jpg/"]
[URL="http://imageshack.us/photo/my-images/689/06072012360.jpg/"][URL="http://imageshack.us/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]

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]

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]

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]

Originally Posted by clean-machines

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]

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]

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://imageshack.us/photo/my-images/207/dscf0182i.jpg/

http://imageshack.us/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]

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

[clean-machines]

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]

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.

[retiredcaps]

Originally Posted by clean-machines

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

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

Follow the instructions in my sig file exactly.

[budm]

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

[budm]

IC2 is for the PFC/Voltage booster circuits, if it does not work (voltage on the main DC cap did not go up), the other power supply will not function (it will not affect the Standby power supply). So you will have to figure out why the PFC is not working.

[clean-machines]

thanks bud m well so far iv re worked the board (all the solder sm and thru hole also esr all the caps i had two that were not getting s reading due to being in circuit took them out and they teste fine

well bud m as we dont seem to be able to find the datasheet on this (i cant ) im not sure on pin outs but i did find potential of 5 volts and 8 volts accross the chip

this is when in standby and booster is off

when however the ps attempts to power up / boot , those potential differences i have accross certain pins die to almost nothing 0.1 and 0.27

so am stuck again for now, unless the ic is faulty

bud m if the pfc chip is faulty would it stop the power supply booting up? i was under the impression this was just a filter for new regulations to stop interference with the supply line i,e not inside the telly but the wiring of the house and power lines etc ?
but i could be so wrong tho!?!?

[tom66]

Try replacing the tiny cap across Vcc, the startup cap. It can cause this kind of issue.

[budm]

Without the IC pin out it will be real difficult to troubleshoot the problem, this power supply looks so familiar to me, it looks the same as used in some Philips TV.
Can you get the P/N as printed on the board?
If the booter circuits not working the 24v will not be working either.