Westinghouse W1603 TV Repair

[Monkeh]

Something connected to the 3.3VSB rail is either drawing excessive current, or the power supply is unable to handle the normal current it does want. The main 3.3V rail is generated by a 5A(!) capable LDO from the +5V rail, which itself is generated from the +12V rail by a buck converter. Clearly the LDO is stiff enough to handle whatever demand is placed upon it.

Find L215 (should be near IC204, the LDO) and measure the voltage across it. It's not exactly a current shunt, but it may serve the purpose. It's rated for 2A at best, so if you see upwards of 20mV across it, that's a pretty clear indicator of a fault. If it's a very low value I'd suspect a weakness in the power supply.

The main 3.3V is only generated after the 3V3SB is sent back on the Power ON line and the reg 12VDC is sent from the power supply board to the main board.
I'd think it's something on the standby voltage circuit that's pulling the voltage down, like maybe C209 or C210 ?

If C209 or C210 were at fault the rail would most likely stay down. It apparently maintains fairly normal voltage once the supply is started and the TV running (I'm not sure how the TV could operate if it didn't, seeing as it powers the main oscillator and holds the supply on..), which means either it's being held up by the main rail or switched out in favour of the main rail (internally to the MT5386). Either way, the main rail will show the current loading if that's the issue.

[Gyro]

Well, isn't the world a calmer place this morning...

Just reading back through the last page or so - post deletions have made it look as if people have been making  type responses to perfectly reasonable suggestions. 

New readers of the thread need to be aware that a large number posts have been deleted and so there is some loss of context! (Applies to the Dumpsterdive TV repair thread too).

[aquamon]

http://forum.allaboutcircuits.com/threads/sony-kdl-32l5000-will-not-turn-on.130583/#post-1075476
This hasn't been fixed from September...

[KhronX]

You just had to jinx it, didn't you? 

Well, isn't the world a calmer place this morning...

Just reading back through the last page or so - post deletions have made it look as if people have been making  type responses to perfectly reasonable suggestions. 

New readers of the thread need to be aware that a large number posts have been deleted and so there is some loss of context! (Applies to the Dumpsterdive TV repair thread too).

http://forum.allaboutcircuits.com/threads/sony-kdl-32l5000-will-not-turn-on.130583/#post-1075476
This hasn't been fixed from September...

[pyroesp]

http://forum.allaboutcircuits.com/threads/sony-kdl-32l5000-will-not-turn-on.130583/#post-1075476
This hasn't been fixed from September...

I don't see why that matters. Someone came here because of an issue. As an electronic forum we try to help the best we can (at least that's my vision).
Only OP knows what happened between then and now.
The fact is he's still with non-working TVs and doesn't want to and might not be able to spend money to buy 3 new TVs.
If it were just one, maybe I would agree to buying a new one. But it's not one, it's 3 new TVs.
I can't complain about my job, but even with it, buying 3 new TVs would set me back quite a bit too.

Anyways...

Let's see what OP can find by doing what Monkeh's suggested.

[cheeseit]

This is the first troll I've encountered on this board. Was kinda fun but I'd rather be without so in the spirit of Christmas and all, please just stop. All those post deletions also ruins the flow and gives the wrong impression of this forum so I hope the mods just ban/delete the user and leave their posts in the future.

[Fisher77]

This is the first troll I've encountered on this board. Was kinda fun but I'd rather be without so in the spirit of Christmas and all, please just stop. All those post deletions also ruins the flow and gives the wrong impression of this forum so I hope the mods just ban/delete the user and leave their posts in the future.

I agree. Just love his signature to. He is a real class act

[KhronX]

"Welcome to the club"... 

This is the first troll I've encountered on this board. Was kinda fun but I'd rather be without so in the spirit of Christmas and all, please just stop. All those post deletions also ruins the flow and gives the wrong impression of this forum so I hope the mods just ban/delete the user and leave their posts in the future.

I agree. Just love his signature to. He is a real class act

[Fisher77]

From the schematic the power on goes through transistor Q210. There's a test point TP001 you might want to measure.
If it's high then the transistor should put the 3.3V (minus the Vce) on the power on.

Voltage on TP001 with the 3.3V jumped to ps_on is 0.5V, without the jumper it is 42.3mV.

Something connected to the 3.3VSB rail is either drawing excessive current, or the power supply is unable to handle the normal current it does want. The main 3.3V rail is generated by a 5A(!) capable LDO from the +5V rail, which itself is generated from the +12V rail by a buck converter. Clearly the LDO is stiff enough to handle whatever demand is placed upon it.

Find L215 (should be near IC204, the LDO) and measure the voltage across it. It's not exactly a current shunt, but it may serve the purpose. It's rated for 2A at best, so if you see upwards of 20mV across it, that's a pretty clear indicator of a fault. If it's a very low value I'd suspect a weakness in the power supply.

As far as loading the standby rail goes, somewhere in the 20-50ohm region should be enough to determine if the supply is weak - it should have no problem with supplying such a load with no notable droop. Be warned typical small resistors will get quite hot, quite fast, but they'll do the job.

With the 3.3V jumped to ps_on, L215 has 14.4mV across it. Without the jumper, L215 has 0.00V across it.
I loaded the 3.3V with a 39ohm resistor. The voltage remained at 3.3V. Never dropped. The resistor did not get hot, just a little warm, I could hold it between my fingers and barely feel it was getting warm. Dont know if that means anything.

[Monkeh]

With the 3.3V jumped to ps_on, L215 has 14.4mV across it.

At least 1.4A. That's enough to at least make me suspicious.

I loaded the 3.3V with a 39ohm resistor. The voltage remained at 3.3V. Never dropped.

I'd call your power supply healthy enough.

So the problem is most likely a component on the +3V3SB rail being faulty - there's not much there. A couple LEDs, the switch board, and.. the main processor.

If you happen to have a power supply with some gusto (a spare PC PSU perhaps), feed the 3V3SB rail with it (no need for the main power supply board) and see what sort of current is drawn and what gets hot. Money's on IC401.

[Fisher77]

I have a spare PC supply. I will hook it up when I can, and post back. Thanks for all the help guys.

[Fisher77]

With the 3.3V jumped to ps_on, L215 has 14.4mV across it.

At least 1.4A. That's enough to at least make me suspicious.

I loaded the 3.3V with a 39ohm resistor. The voltage remained at 3.3V. Never dropped.

I'd call your power supply healthy enough.

So the problem is most likely a component on the +3V3SB rail being faulty - there's not much there. A couple LEDs, the switch board, and.. the main processor.

If you happen to have a power supply with some gusto (a spare PC PSU perhaps), feed the 3V3SB rail with it (no need for the main power supply board) and see what sort of current is drawn and what gets hot. Money's on IC401.

Just to make sure I am on the same page, you want me to feed the 3V3 stby pin on the main board with the CPU PS 3V3 output. Is that correct?
If that is correct, the IC401 got warm, I would not call it hot, just enough to tell there was a temp change. The current draw was .55 amps.

[Monkeh]

With the 3.3V jumped to ps_on, L215 has 14.4mV across it.

At least 1.4A. That's enough to at least make me suspicious.

I loaded the 3.3V with a 39ohm resistor. The voltage remained at 3.3V. Never dropped.

I'd call your power supply healthy enough.

So the problem is most likely a component on the +3V3SB rail being faulty - there's not much there. A couple LEDs, the switch board, and.. the main processor.

If you happen to have a power supply with some gusto (a spare PC PSU perhaps), feed the 3V3SB rail with it (no need for the main power supply board) and see what sort of current is drawn and what gets hot. Money's on IC401.

Just to make sure I am on the same page, you want me to feed the 3V3 stby pin on the main board with the CPU PS 3V3 output. Is that correct?
If that is correct, the IC401 got warm, I would not call it hot, just enough to tell there was a temp change. The current draw was .55 amps.

I don't have any numbers for that chip, but to run an oscillator and wait for a startup command, that seems hugely excessive. I'm willing to bet it's broke.

If anyone can figure out a current path outside IC401, though..

[Fisher77]

I pulled the main board out of the tv. Laying on my bench I fed 3v3 to the stby pin of CN201. I was just probing around checking voltages and decided to check the voltage on CN4201 that goes to the button module on the side of the tv. I noticed I have 2.7 volts on pins 5,4 and 3 of that connector. Now pin 5 looks to be the 3.3 volt supply to the module. Pin 4 is for the power button. And pin 3 is the ADC_IN2(whatever that is). Now is there supposed to be voltage on pin 4, without pressing any button? ( Pic attached)

The reason I ask is that I also noticed that the ps_on pin of the CN201 connector that goes to the PS board has 2.7 volts when there is nothing telling the main board to power on the tv.

Is this conformation that IC401 is toast?
And if the ps_on pin is constantly being fed voltage, why is the tv not just turning on when it is plugged in?

[Monkeh]

The power on signal is active low, it expects it to be taken down to ground.

2.7V is strange, that should be at 3.3V.

[pyroesp]

Pin 4 is connected to +3V3SB through pull-up resistor R4202.

[Fisher77]

The power on signal is active low, it expects it to be taken down to ground.

2.7V is strange, that should be at 3.3V.

I thought 2.7v was strange to.

[Fisher77]

Pin 4 is connected to +3V3SB through pull-up resistor R4202.

Missed that this morning. Tired eyes I guess.

[Fisher77]

I was checking some more on this main board and found something else that seems odd to me, but it could be normal. When I am feeding the stby with 3.3 volts I still have the 2.4 to 2.7 volts on the P ON ping. But I also noticed I am seeing 1.4 volts on the regulated 12V pins as well.  Is that normal?

Something else I noticed is when I have the meter on continuity(buzz) and probe the 3.3V stby pin and the ground pin the meter buzzes away, never stops. I know that setting pretty much gets you from point A to B, but curious if that should be happening. Certainly dont happen on the PS_ON pin,  REG 12V pins, or the UNREG 15V pins.
I did ohm from the stby pin to ground and it measured 23.4 ohms.

[Monkeh]

No, it really should not measure that low.

Something, almost certainly IC401 (there's pretty much nothing else connected directly to the rail) has a major internal fault. It's likely not repairable.

[Fisher77]

I do beleive you are absolutely right Monkeh. Looks like the only fix is to get another main board. Shopjimmy has none. Found plenty on ebay, but getting one off of ebay that is good can be a challenge in itself. I have read the stories of it taking 3 or 4 boards before a person gets a good one.

A big thanks to everyone who has helped mo out with these two tv's!!

I will post back with the resuslts when I get the part installed for the Westinghouse.

Next will be an HP computer, but I figure the mobo is probably toast. Only way to find out is to crack it open and see. I will start a new thread for that one when I get to it.

[Fisher77]

Ok, on the second tv, its a Vizio that I found a blown FET and Diode on, I also found a blown resistor. It is a 0.27 ohm resistor. I have found a 0.24 Ohm resistor on another scrap board I had lying around.

Will 0.24 ohms be close enough to 0.27 ohms, or do I need to order the 0.27 ohm resistor? They are 5% resistors.

I have also located a 0.35 ohm, if more would be better than less.

[KhronX]

That would depend entirely on where it is, on the schematic / what role it has in the circuit.

Let me guess - it's on the primary side, between the source of the flyback switching MOSFET and ground?
With the blown FET, that makes sense.

I'd also expect a potentially blown PWM controller chip, so be mentally prepared for that too.

Either one would be fine, although i'd lean towards the 0.24 one.

[Fisher77]

That would depend entirely on where it is, on the schematic / what role it has in the circuit.

Let me guess - it's on the primary side, between the source of the flyback switching MOSFET and ground?
With the blown FET, that makes sense.

I'd also expect a potentially blown PWM controller chip, so be mentally prepared for that too.

Either one would be fine, although i'd lean towards the 0.24 one.

You are correct KhronX. It is between the source ans ground. Guess I should have pointed that out .

One other option is to parallel a 1.5ohm with a .35 ohm for 0.28 ohms. Plenty of room on the board for it.

I am sure your prolly right about the PWM controller chip. Wouldnt surprise me on bit.

[KhronX]

I wouldn't lose any sleep over that. With 5% tolerances, the 0.24 one could actually be as high as 0.252, and the 0.27 could be as low as 0.257 

And besides, i quite doubt the tv's (normally) running anywhere near what the PSU can provide, so there's some leeway there, as well.
These things are rarely (if ever) designed "right on the edge" - unless we're strictly talking cost