Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

[Roktaal]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Hi guys.
If I may hijack this thread as I have same issue with Vestel 17IPS20 V6.
After a lightning storm, power board died burning D112 and D114 along with the FS100. After replacing those board was still dead. After reading in this thread about U202 I found out that pins 5 and 6 are shorted. D298 came out as ok as well as C296 but C295 appears to be dead. I removed all 3 yet pins 5 and 6 were still shorted so I assume U202 is dead.
Tomorrow I'll buy new FAN6300A as well as replacements for those condensers. My question is can someone confirm that both C295 and C296, according to schem provided by Dannyx, are 1uF 50V since the two I removed from the board differ in size.

[bolob]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Sorry for letting you wait long. I have been out for long weekend, hopefully today afternoon I can deal a bit with the TV again. I will attach the requested pictures soon.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Thanks for setting me straight on the backlight operation. It's sad, but I haven't worked on a TV for what seems like ages, so I forgot all the differences between models that I used to know by heart...

[budm]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

ST_BY pin is PS-ON pin, it should change state when power switch toggle on and off, in this TV the ST_BY (PS-ON) is active low.
So do you have switched 12VDC? Do you have PFC Boosted Voltage on the main filter caps (measure it between the two legs of the cap)?
Can we see good clear straight shots pictures of the whole power supply board and the whole backside of the TV showing all the boards?
Please note that the schematic shows all the parts for making the circuit board so your circuit board assembly used in your TV may not have all the parts as shown in the schematic.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

My best guess at the moment is that you have a bad mainboard with a short somewhere, though I must admit I haven't had a 17mb82S do this so far, but there's a first time for everything. This supply has no separate 5v standby output - it always supplies 12v to the main board which then handles standby on its own, if I remember correctly. Try testing your TV in "blocks". Here's what I do.

You can try feeding the board 12v from a separate supply to see what happens, ideally a bench supply so you can monitor the amps it draws. You won't have any backlight if you try it like this, but you should still see the TV coming on by looking at the screen with a bright light like I mentioned (IF the MB is functional !). Can't tell for sure how much current a functional board should draw, but if the amps start to go crazy and the supply shuts down or enters CC mode (if it's a bench-top supply set for a low current limit), you know you've got a problem somewhere on the MB and should dig deeper. Fortunately you can find schematics for Vestels relatively easy.

That 12v output can also be loaded with a 12v car lamp for testing purposes if you don't have an adjustable load. It should remain stable as the bulb comes on. A PC fan could also be used (or perhaps several of them, since they're pretty light loads).

[bolob]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Hi,

I did some measurement in the CN4 connector. 2,4,6,8 pins are DGN, on 10, 11, 12 pins I can measure 12.48V.
I also checked the pin 1 which has name in the schematic as PIN_1, only few millivolts I can measure which is not stable 1-3.5mV. After connecting the connector to the main board, the voltage on the 10,11,12 (all the three are sorted in the PCB) dropped by 0.02 Volt. So, seems there is no huge load from the main board.

ST_BY : remain close to 0V (actually 18mv) when the led blinking and after as well
BL_ON/OFF : Wile the led blinks almost 0V, when the LED went off this pin will have 5.2V.

PWM_DIMM : while the LED blinks 3.3V after 1.9V
On the backlight LED connector :
No voltage, except for few milisec. when the board swiching the 5.2V to the BL_ON/OFF pin I can see some change in the digital multimeter, 2-3V value, but shortly going to be 0 again, and stays as it is. (CN501, pin1 and 7 where the backlight is connected)

[bolob]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

HI Dannyx,

Thanks a million for your reply.
Before I am starting to measure some voltage in the connector, I want to make clear about some conditions.
Should I connect the main board to the PSU and make the measurement by that way, or, can I do it the main board disconnected status from the PSU as well ?
Also, I just wondering, might I can use the LM7805 linear regulator connected to the 12V VCC and give the ST_BY pin supply if it is necessary. ( Sorry I didn't went deep enough to understand the schematic fully, but I guess to start the PSU in full fuction way, I need to supply some voltage (might 5 V ?) to the ST_BY pin in the CN4 connector.
As I checked the pictures what you attached to your post, my board looks completely the same as you have/had. only difference my PCB is not that brown around the FET (Q301) . Also by analyzing the boar, this guy doesn't have the +5V stabilizer, so the pin +5_STBY in CN4 is not connected to anywhere in the PCB. The jumper and all the regulator parts are not installed. So, my expectation if I connect the PSU to the main, I supposed to measure the 12V in the connector, even it is not pugged into the main board socket. Right ? By the way, the main board is 17MB82S.
Regarding your question, about what was the behavior of the standby led whe the TV was operating, well..... we are not sure. As I remember the LED was on when the TV was off, so it was signing standby function. According to my wife it was on when the TV was on.... brrr... sorry, the TV was in the kids room, so we not really often were checking it. Also kids only 5 years old, they don't remember for it.
I will try to come back within today with some measurement result from the PSU connector directly without connected to the main board.
Thanks for your help in advance.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Can you see any picture on screen by shining a bright flashlight onto the screen ?

How was the LED behaving when the TV WAS functional ? Was it off when the set was on and red when off ?

Measure the voltages present at the connector between the main board and the power supply - there should be a pinout printed on the board to help you and some pictures of your board would also help.

[bolob]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Hi Guys,

I have a 40" Technika LED TV (Tesco brand) using the 17IPS20 -R6 PSU. Few days ago the problem started with the TV, no picture, but sound still it has. (I haven't seen this condition my wife told me) so I am not sure the backlight went off, or there was no video as well that time). She tried to power off and on, but after sound also disappeared. The current condition , after connecting the plug to the main, the red standby led flashing 7 times and after going to be off. It didn't try to switch on the backlight, also no electrical sounds coming form any transformers/coils. I was checking all the diodes, and transistors, I couldn't find any shorted or broken one. Any advice with this would be highly appreciated. In the above described condition, should the board supply any voltage for the LED strips ? Is there any sense to check the voltage in the connector of the backlight ? Or what is the easiest way to identify the problem with the board or with the backlight itself ?

Thanks in advance,
Br,
/bolob

[robertkendrick]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Just a note to say I also had the same problem with C397. It was reading about 250 ohms each way. Replaced and now TV up and running.
My 17IPS20 R6 board was pulsating on the first controller. Something was pulling it down.
The first IC controller is fed from VCC_Main while the other two from VCC. I found it convenient to remove Q216 (an ordinary transistor) from the board which isolated the other two controllers from VCC. This brought the first controller back to life with correct voltages on the secondary transformer windings. Then it was a question of finding where the problem could be. OP, thanks for all your help.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Yes, it is - time for a new board then.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

I did that also from my bench psu and the main chip got warm enough before it blew my psu 5Amp fuse.
I think its clear that the main chip is bad.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

A battery is not enough if something is shorted. You really need to pump that SOB full of amps to really get a feel for it - it's damaged anyway, so nothing to lose as long as you don't exceed that rail's nominal voltage, so if you're getting a short on the 3.3v line, you won't go higher than that.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

You can apply 1-2 volts on that 3.3 volt line using a battery or current limited supply, and look for what gets hot, just apply voltage for a few seconds at a time. It might just be a small ceramic cap.

I did that before and came up empty. I just shorted the battery.

I doubt it is a ceramic because ive checked pretty much all of them on the board. I suspect the Audio chip or the main chip that gets warm when i plug the psu in. Most probably the 2nd like you suggested "getting hot".

[petehall347]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

i have a habit of poking around from original found short to other places . if both places shows short to next suspect you are very close .

[R_J]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

You can apply 1-2 volts on that 3.3 volt line using a battery or current limited supply, and look for what gets hot, just apply voltage for a few seconds at a time. It might just be a small ceramic cap.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

I will short enough. As for the mainboard, there is a problem with the 3.3V. The 5V line is fine but the lm1117 reads short between the output and GND. The lm1117 is burned but it is not the only thing. after removing it the short was still there. ive checked all the chips i could and found nothing bad so the problem could be in many different places. So many circuits are powered from the 3.3_stby like audio, video etc. At this point i thought that i should order an other board.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Louis Rossmann got me into schematics and how to follow them. It helps in the realm of TVs as well - go check him out on Youtube if you haven't already.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Good day to all !
I am now investigating the Mainboard voltage supply chips. Afer following your guidelines i have realized how important it it to be able to read a schematic and understand it ! Ill keep you posted.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Ok, so what's the state of this project thus far ? I see you've edited your original reply.

You can use the trick I mentioned earlier with feeding 12v from an external supply, although you should've at least got the standby LED to come on if its PSU is functional and outputs something like you said.

Page 5 of the schematic is what you're interested in. Follow the power from the connector on the left (either CN2 or CN3 depending on your model) and see where it "stops". Does your connector correspond with CN2 or CN 3 ? Do you get 12v and 24v where it's supposed to according to that pinout ? If not, check to make sure those lines are actually populated, since often with Vestels the pin is there but the components are missing, therefore you'll have no voltage present there either. For instance this particular board also shows the option for a DC adapter at the bottom of the page, which I'm betting is not what you have, so you have to identify what you're working with first. Vestel service manuals are generic and apply to all the different variants of that board instead of having dedicated individual schematics for each model....most confusing...

12vSTBY should go into U9 where it gets converted to 5v on pin 7 (after coil L3) - see if you get 5v. If you don't, see if that output (after L3) reads a short. If it does, something running off the 5vSTBY bus is shorted. To identify it, remove L3, connect a variable supply to where L3 used to be and gently increase the voltage (and current) being careful not to exceed the 5v rail and feel for where the board gets hot. Crank the current up as much as possible without exceeding 5v. The part that gets hot is your culprit. Repeat the process of tracing the power lines like this, from the input to the nearest DC-DC converter until you can provide more data. Everything you need of interest is on page 5 - don't bother with others just yet.

Hello and thank you again. I had issues to attend these days so i have done nothing so far. Tomorrow i work all day so no time for troubleshooting the TV. On friday i will definetly give it a look and get back to you with more readings.

THANKYOU !