Westinghouse W1603 TV Repair

[Fisher77]

Ok, here is the rub. The power line going into my parents house got zapped by a lighting bolt. It knocked out 3 tv's, a satellite box, satellite dish components, 1 computer, 1 light fixture, 1 light switch, 2 GFCI socktes, and threw just about every breaker in the house. In other words, it did a number on the house. My dad compared the ensuing thunder crack to the sound of a 155mm Howitzer shell impacting the earth. He would know(1st Calvary Division '66 to '67). I am hoping to get some help with this tv, and possibly the other 2 tv's to help take the burden of my parents pocket book. I figure the mobo got zapped on the computer, so it is probably toast, but well, I'll crack it open anyhow to take a look.

This Westinghouse is the first of the 3 tv's. Here are the voltages on the power supply output:

+12V = 0V
+12V = 0V
GND
GND
+3V = 0V
+5V = 0V
GND
GND
On/Off = 0V
DIM = 0V

With those voltages listed I am pretty sure this power supply is graveyard dead. I have checked everything I know how to check on it. There is one diode, D909, that I am getting .018 both ways when I check using the diode check on my DMM. With that being said, I assume it is a Zener by the way it looks.  But I may be wrong,  It is in the red box in the pic. I have checked all of the resistors, and the diodes, and caps on the bottom that I could without pulling them out of circuit. I have really come to hate most smd components because unless you work with them alot, then 3/4's of the time you dont even know what the hell it's value is. The resistors are usually marked well, why they cant do the same with the caps and diodes is beyond me. The MOSFET Q901 has voltage to the drain. I pulled it off of the board, and checked it. It is switching as it should. That is about all I can do up to this point. Any help with this would be greatly appreciated!

[Fisher77]

Here are the pics of the power supply board:

Third pic shows the diode I was talking about.

https://i.imgsafe.org/21fc437702.jpg
https://i.imgsafe.org/21fc86dcc7.jpg
https://i.imgsafe.org/21fcb47858.jpg
https://i.imgsafe.org/21fcfd2808.jpg
https://i.imgsafe.org/21fd442c6e.jpg

[pyroesp]

Hello Fisher77,

Well that sucks... Hopefully more knowledgeable people than me will be able to help you out.
From the looks of the components on the underside of the PCB, D909 is a "simple" diode. Look all the way left, right next to the connector CN902, there's a diode labelled ZD920, which I guess stands for zener diode.

You mention that you have power on the drain. The next step should be to "chop" the voltage (see block diagram below). An optocoupler (IC903) should be used to drive the gate of the MOSFET as a feedback for a PWM IC which drives the MOSFET gate. Does the optocoupler still work ? Does it receive a PWM (or other square wave) signal ?

(from wikipedia)

EDIT1:
It might be interesting for you to find and watch some SMPS repair videos. They're always helpful and might point you to the right direction.

EDIT2:
If you can not get it to work, you might be able to find one on ebay or aliexpress.
Let's just hope it's only the power supply that blew up and the main processor of the TV is ok.

[Fisher77]

The optocoupler is still good, I pulled if from the board and tested it a little bit ago. The collector of the optocoupler is connected to pin 2 of IC901. Pin 5 of IC901 is connected to the gat of the MOSFET. IC901 is a LD7575PS.

As far as the PWM to the optocoupler, I do have a scope. Its a older crt that I am still learning to use. If you can tell me where/how to connect it, I will check for the signal.

Edit: I noticed I have continuity between all the pins on the T901. Also have continuity between the positive side of C930 and all the pins on T901. Is this normal? Dont seem right to me.

I have outlined all the pins in the pic https://i.imgsafe.org/2eefae445a.jpg

[pyroesp]

What model oscilloscope do you have ?

T901 is your output transformer, which is basically a wire.

[Fisher77]

Tektronix 2205

[pyroesp]

My bad I said something stupid. The optocoupler is just used as a feedback of the output voltage to the PWM IC, it does not drive the mosfet. 
You should be able to measure the voltage on the LED side of the optocoupler with a multimeter.

If you want to know how to use your oscilloscope:
Here's a video Dave made on a Tektronix 2225, which is almost identical to the 2205:

Here's another one on how NOT to blow your oscilloscope up:

[Fisher77]

Thanks for the videos. I will definitely watch them, prolly more than once. As for the optocoupler, it has 0V on the LED side, and 0V on the emitter and collector.

[pyroesp]

IC901 looks like it's the mosfet driver. Try to find it's datasheet and see how it works/turns on. Can't see the part number of IC901 on the pictures.

[Fisher77]

It is a LD7575PS. Here is a link to the datasheet, if you would like to have a look: https://lib.chipdip.ru/923/DOC000923326.pdf
I traced the tracks, and it is definitely looks like it is supposed to drive the mosfet.

Here is what I am measuring on the IC:

1:0V has resistor to ground
2:0V
3:0V
4:GND
5:0V
6:11.6VDC
7:NC
8:145VDC

[pyroesp]

Pin 5 should send a PWM signal to the gate of the MOSFET for it to turn on and off, which will generate an AC voltage on the transformer.
Something you could check is the resistor to ground on pin 1 (RT). From the datasheet, this resistor selects the frequency, see p.10. But also, if it were to short (RT to ground) or break (RT floating), then the IC goes into fault protection.

Other than that, I'd guess it blew up. You could find one on ebay for cheap.

[Fisher77]

Resistor is good. I guess I will order a new LD7575PS , and see if that does it.

[Fisher77]

Thanks for the help pyroesp. I ordered a new LD7575PS today. Be a couple of weeks before I see it. When it gets here and I get it in, I will post back.

[pyroesp]

Glad to help, altough I would have liked someone else to pitch in and correct my stupid mistake(s?)  or give other tips.

In the mean time, let's see what's wrong with the 2 other TV's. You should be able to apply the same troubleshooting.

[Fisher77]

On the second tv I found a blown MOSFET, and a blown Diode. I had to order them as well. Hopefully that will be all that is wrong with that one. The third tv I have yet to find a problem. I will post pics of the PS as soon as I get a chance.

[Fisher77]

Here are pics of the third tv's PS board. It is a Sony Model KDL-32L5000

Here are the voltages:
P ON = 0V
AC DET = 3.3V
STBY = 3.3V
UNREG 15V = 0V
REG 12V = 0V


https://i.imgsafe.org/70006bb981.jpg
https://i.imgsafe.org/7001003596.jpg
https://i.imgsafe.org/6fffd634ea.jpg
https://i.imgsafe.org/70022d3371.jpg
https://i.imgsafe.org/7002916035.jpg
https://i.imgsafe.org/701d1871f9.jpg

Now what would happen if I jumped the 3.3 STBY to the P ON?
Is it possible that would turn the PS on and I would see the other voltages indicating a problem on the main board of the TV?

[pyroesp]

I think I found the schematic while googling a bit (click the download button): http://www.electronica-pt.com/esquema/func-startdown/29241/
Check if the PCB matches the schematic, always helpful for troubleshooting if it is.

The fact that the Power On comes from the controller board, means there's probably something wrong there.
Maybe you could check the controller board to see how it sends the Power On signal (probably from CPU).
I think you can try to bypass the controller board, but try to check the components on the Power On circuit first to make sure you have no short to GND.

[Fisher77]

Ok, I checked the PS over. I found nothing wrong. I finally jumped the stby 3.3v to the ps_on pin on the power supply while I had my meter connected to the 12V regulated output. The power supply kicked on and the meter was reading 12.3V. I then checked the 24V output on the other side of the power supply that supplies voltage to the back light inverter, and it read 24.4V. Looks like the power supply is good. I will have to do my best to trace out the ps_on, and stby circuits on the main control board. I will post some pictures of it in a bit.


Here are the pics:
https://i.imgsafe.org/8a34203af3.jpg
https://i.imgsafe.org/8a346e936e.jpg
https://i.imgsafe.org/8a347b8547.jpg
https://i.imgsafe.org/8a34bb9083.jpg

[KhronX]

Aaaaand where's someone supposed to get the content of whatever (E)EPROMs and flash chips, hmm?

I doubt anything's gonna start without something to boot (from) 

Never been a fan of the shotgun approach...

The fact that it got zapped by lightening, I would not waste my time or $$$ on it.

Replace ALL I.C's [including (E)Eproms]--->start.

[Fisher77]

Aaaaand where's someone supposed to get the content of whatever (E)EPROMs and flash chips, hmm?

I doubt anything's gonna start without something to boot (from) 

Never been a fan of the shotgun approach...

The fact that it got zapped by lightening, I would not waste my time or $$$ on it.
Replace ALL I.C's [including (E)Eproms]--->start.

And will a EEPROM prevent the TV from turning on?

I know one damn thing, I can jump the 3.3V stby to the ps_on, and turn the tv on with the on/off button on the side of the tv.

[Fisher77]

What's happening now?

Got "snow" on screen?

No snow. It powers on the the startup screen with "no signal" on the screen. I will have a look at the 5v rail and post back. Thanks auqamon.

And will a EEPROM prevent the TV from turning on?

This TV?
YES!

But I am "not supposed to know anything about these TV's"...

You need to start on the 5 Volt rail.<-----START.
Which comes after the 12V.

Didnt intend to step on your toes. I was simply asking if the eeprom will keep a tv from turning on. I dont know what all the eeprom does. I have fixed a few tv's in the past, but they were always a power supply issue, mostly blown caps. This is the first time I have dealt with an issue on the main board. I would like to be able to fix it for my parents, and at the same time learn a little more about how all this works.

[KhronX]

If it gets as far as driving the LCD panel and backlight enough to say "no signal", at least to me, means that most of the essential blocks are working just fine, including the main processor.

Does it say that, regardless of the selected input? Or only on the TV/cable input?

What's happening now?

Got "snow" on screen?

No snow. It powers on the the startup screen with "no signal" on the screen. I will have a look at the 5v rail and post back. Thanks auqamon.

Most (if not all) LCD TV's are basically an all-in-one (stripped-down) computer nowadays. They have a processor, and they boot an operating system from an on-board memory chip (usually flash-based) - in some cases a version of Linux, in the case of some smart-tv's it's a flavour of Android, etc.

The EEPROM is another form of electronic data storage, but more often quite small in size, and it usually holds stuff like calibration data, or system ID stuff - small-sized but occasionally essential data for the functioning of the whole system

I was simply asking if the eeprom will keep a tv from turning on. I dont know what all the eeprom does. I have fixed a few tv's in the past, but they were always a power supply issue, mostly blown caps. This is the first time I have dealt with an issue on the main board. I would like to be able to fix it for my parents, and at the same time learn a little more about how all this works.

[Fisher77]

Thanks for the explanation of the eeprom KhronX. I had seen people talking about it on forums, but never knew what it did.

Does it say that, regardless of the selected input? Or only on the TV/cable input?

I just checked, and it does say that on all inputs. I hooked a dvd player to all the inputs, with the exception of the HDMI inputs of course, and it showed the movie I had in the dvd player.

[KhronX]

Ok, now i'm getting confused

On one hand, "it does say that on all inputs", but on the other hand, "it showed the movie I had in the dvd player" on the s-video / scart / composite (?) inputs.

So which one is it? 

[Fisher77]

Ok, I went through all the inputs, AV, composite, hdmi, tv/cable, and PC and it had the "no signal" on all of those selections.


Then I hooked up a dvd player and checked the AV, composite, and tv/cable inputs with a movie playing in the dvd player, and saw the movie on the screen.