Issue with Westinghouse 19" LCD Monitor (large pics)

[PlainBill]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

What cap did you mean? I looked at the circuit but i did not see a cap connected to that transistor.

Your questions seems very plausible but i just dont know the answer......wish my electronics was better.

Look at the attached picture. The controller IC (U200), everything within the blue outline, and the two power FETs (solder points circled in black) are the driver circuit for the inverter transformer. Pin 8 of U200 drives the gate of the lower transistor directly. The gate of the other transistor is driven by Q208, driving through R210. The drive to the transformer is coupled back through C234. Without a schematic (or maybe even with one ), I'm having trouble figuring out just what is happening in this circuit.

PlainBill

[dondrusco]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

I still haven't tried to generate a schematic, but I notice there is a capacitor in that circuit. Could it be that it is holding enough charge to turn the FET on?

PlainBill

Hi,

I found only paid sites with schematics. This power board is the same, as in Acer AL1916W (probably you know about it)

http://www.s100-manuals.com/search.asp?q=AL1916W

[Welchs101]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Question: Regardless of if a cap is in the circuit........should there be a low resistance of several kilo-ohm between gate and drain?

[PlainBill]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Question: Regardless of if a cap is in the circuit........should there be a low resistance of several kilo-ohm between gate and drain?

Maybe. Notice there are a number of resistors in the circuit. Now if the resistance is there OUT of circuit, that's a problem.

I'm hoping you can find a problem with a component, because the alternatives are to pull the transformer and try powering up the inverter to see if anything blows, or to map the interconnections between 30+ points so it is possible to create a schematic.

PlainBill

[Welchs101]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Do you think i should take the transistor out of circuit and measure it out of circuit?

What do you think of this: What if i were to replace fuse F200 with a "wire" and then power up monitor and try and find device that gets "hot" ........ i am afraid that by doing this something else will "blow" but i am really not sure what to look at to fix this problem.

I am stumped!

[PlainBill]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Do you think i should take the transistor out of circuit and measure it out of circuit?

What do you think of this: What if i were to replace fuse F200 with a "wire" and then power up monitor and try and find device that gets "hot" ........ i am afraid that by doing this something else will "blow" but i am really not sure what to look at to fix this problem.

I am stumped!

Well, I'm not stumped. The problem is there are several tests that you don't have the equipment for. Unless you have been holding out on me, and have a variable power supply, a ring tester, and an oscilloscope hidden in a closet?

The short summary of the dilemma is there are two likely causes of the problem. Cause 1 is a defective component is causing both power FETs to be on at the same time. Presto!!! Shorted FETs, blown fuse. Cause 2 is the inverter transformer has a short - possibly in the primary. Same result- the FETs overheat, short, and the fuse blows.

If you had a variable power supply, using the jumper wire would be a viable approach. The problem with hitting it with full power is that the part that smokes is probably NOT the defective part.

Here is an idea that should keep you out of my hair until after I get back from Hawaii. Hie thee off to ye friendly electronics store and buy a light bulb. Something rated for 12 volts and 1 amp or less. Maybe an automotive indicator light would work. One of the dash bulbs that always liked to burn out would be perfect. (No, I don't know the part number, look up the dash light for a 1969 Dodge Charger with the 426 Hemi). Hook that (the light, not the car) up in place of the fuse, then power it up. If the light bulb glows brightly for a few seconds, then goes out you are probably looking at a problem with the inverter transformer.

Next, remove the inverter transformer. Power up the circuit (using the light bulb instead of the fuse.) If the light bulb glows brightly, the problem certainly isn't the transformer.

PlainBill

P.S. For a Christmas present I am looking for the link to a schematic for the power supply for a LG Electronics DU-42PX12X plasma TV. It's LG part number 3501V00181B. Other numbers are DN-42PY10X AF044A MURATA MPF7413

Pass it on.

PB

[Welchs101]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Hi PlainBill,

No i have not been holding out on you.......i wish i had all that nice kind of equipment.

Hawaii! Can i go? Just kidding.

I will get the bulb and try what you suggested. Do you know where i can get a ring tester for cheap?

Have a nice trip! When will you be getting back?

[PlainBill]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Hi PlainBill,

No i have not been holding out on you.......i wish i had all that nice kind of equipment.

Hawaii! Can i go?

Sure. I'd offer to smuggle you in my luggage, but it's actually cheaper if you buy a ticket.

I will get the bulb and try what you suggested. Do you know where i can get a ring tester for cheap?

Anatek. www.anatekcorp.com

Have a nice trip! When will you be getting back?

It depends on how the surf is. Just kidding, it wouldn't be fair if I entered the contest.

We'll be back before the new moon.

PlainBill

[tanagra]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

[QUOTE=eguevarae]Congratulations. Another unit saved from the landfill ...

I agree, the power of the Internet. I too saved some trash from the landfill. After reading all the posts referencing all of the Westinghouse TVs going bad, I took apart the TV and sure enough I saw the bulge on the cap. I found a correct 2200uf cap installed in a 10 year old pc power supply that was in a box of junk in my closet. I replaces the cap and I actually fixed a junk TV power supply with junk parts. Somehow, that gives more satisfaction than going to Radio Shack! Works great! Thanks!

[kc8adu]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

[QUOTE=tanagra]

Congratulations. Another unit saved from the landfill ...

I agree, the power of the Internet. I too saved some trash from the landfill. After reading all the posts referencing all of the Westinghouse TVs going bad, I took apart the TV and sure enough I saw the bulge on the cap. I found a correct 2200uf cap installed in a 10 year old pc power supply that was in a box of junk in my closet. I replaces the cap and I actually fixed a junk TV power supply with junk parts. Somehow, that gives more satisfaction than going to Radio Shack! Works great! Thanks!

too bad the username junk parts is already taken!

[Welchs101]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Bill,

It has been sometime since i was working on this monitor but a friend of mine gave me a monitor that has the same (almost same board) as this one. I am hoping that between the two i can figure out what is going on with this one.

I took the transformer out of this board. Put a new fuse in. With just the power supply board, i plugged in the power.....fuse DID NOT BLOW! When i was taking the transformer out i did find that one of the blue caps had a cold solder joint. So i resoldered all the connection points of the blue caps near the transformer. Also, i put the transformer back in and power up the supply board. The fuse DID NOT BLOW!

So i decided to connect the supply board to the main board and connect the ccfls as well. This time however when i powered up the fuse DID BLOW.

Any ideas? I know its been a long time since my last post but i would really like to fix this monitor now that i have another monitor with a similar board which may not be working but at least it is not shorting.

[PlainBill]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Bill,

It has been sometime since i was working on this monitor but a friend of mine gave me a monitor that has the same (almost same board) as this one. I am hoping that between the two i can figure out what is going on with this one.

I took the transformer out of this board. Put a new fuse in. With just the power supply board, i plugged in the power.....fuse DID NOT BLOW! When i was taking the transformer out i did find that one of the blue caps had a cold solder joint. So i resoldered all the connection points of the blue caps near the transformer. Also, i put the transformer back in and power up the supply board. The fuse DID NOT BLOW!

So i decided to connect the supply board to the main board and connect the ccfls as well. This time however when i powered up the fuse DID BLOW.

Any ideas? I know its been a long time since my last post but i would really like to fix this monitor now that i have another monitor with a similar board which may not be working but at least it is not shorting.

Which transformer, and which fuse?

PlainBill

[Welchs101]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

The transformer that is just before the ccfl lamps.

The fuse is on the back of the board and it kept blowing. It has a "W" on it. i can send pics again if you like.

[PlainBill]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

The transformer that is just before the ccfl lamps.

The fuse is on the back of the board and it kept blowing. It has a "W" on it. i can send pics again if you like.

Got it.

I'm not going to go over the thread to get history of this board, but off the top of my head there are two possibilities. Shorted transistor, or shorted transformer.

As I indicated, this board is notorious for shorted transistors. With the logic card disconnected the inverter controller would not get the BL_ON signal. If both transistors were shorted, the fuse would still have blown. If only one transistor or the transformer was shorted the fuse would not blow. Then you added the logic board, which sent the BL_ON signal.

PlainBill

[Welchs101]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

I have another transformer from a similar type board/monitor. This monitor has a "different" issue, ie....fuse is not shorting.

1-I could swap transformers and see what happens.

Beyond this i am not sure what to do. The boards are almost identical if that helps with any ideas.

If you need additional pics or any info....let me know.

Thanks again for your help!

[Welchs101]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Would you like me to start a new thread. This one is kinda long. We can start over ......maybe the best thing anyway.

[PlainBill]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Would you like me to start a new thread. This one is kinda long. We can start over ......maybe the best thing anyway.

Well, I'm getting confused.

First you said:

Bill,

It has been sometime since i was working on this monitor but a friend of mine gave me a monitor that has the same (almost same board) as this one. I am hoping that between the two i can figure out what is going on with this one.

I took the transformer out of this board. Put a new fuse in. With just the power supply board, i plugged in the power.....fuse DID NOT BLOW! When i was taking the transformer out i did find that one of the blue caps had a cold solder joint. So i resoldered all the connection points of the blue caps near the transformer. Also, i put the transformer back in and power up the supply board. The fuse DID NOT BLOW!

So i decided to connect the supply board to the main board and connect the ccfls as well. This time however when i powered up the fuse DID BLOW.

Any ideas? I know its been a long time since my last post but i would really like to fix this monitor now that i have another monitor with a similar board which may not be working but at least it is not shorting.

Then you said:

The transformer that is just before the ccfl lamps.

The fuse is on the back of the board and it kept blowing. It has a "W" on it. i can send pics again if you like.

I gave some advice, next you said:

I have another transformer from a similar type board/monitor. This monitor has a "different" issue, ie....fuse is not shorting.

1-I could swap transformers and see what happens.

Beyond this i am not sure what to do. The boards are almost identical if that helps with any ideas.

If you need additional pics or any info....let me know.

Thanks again for your help!

Now in another thread you have a monitor with a similar power supply / inverter, but no CCFL action whatever. In this thread you said you have a power supply / inverter that blows the fuse. But now you say

fuse is not shorting

Aside from teh fact fuses very rarely short, one or more of us is very confused. Another thread isn't going to help that!

It seems to me you have two monitors, both with Delta power supplies / inverters. One blows the inverter fuse, one has no inverter output. I'm pretty sure I can keep track of which is which, in spite of the fact I'm repairing sprinkler lines, fighting off biting ants, wondering what to do about dinner, planting bushes, wondering how much it's going to rain, trying to decide what to do about the bees that are swarming, and planning a dinner good enough my wife won't be upset!

PlainBill

[gfgray]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Wow, you guys are hard core. Bill suggested earlier this could happen if both FETs are conducting. Can you check for a short between the gates of the two FETs?

[Welchs101]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

yes, there are two threads...........for two different monitors with two different issues. They do have the same (almost identical) power supply boards so i was hoping that i could use parts from one or the other to figure out what was wrong.

I dont want to confuse the threads anymore than i have already. I appologize for that but i was trying to be careful not to confuse anyone (believe it or not).

I will measure the FETS for the other monitor in that thread. But i can tell you that the fuse is not blowing because of the FETS........how do i know this......because the fets that were in the monitor that kept blowing the fuses are now in the acer monitor (ya know the one in the other thread) and they are not blowing the fuse...........

[gfgray]

Re: Issue with Westinghouse 19" LCD Monitor (large pics)

Yes, I am asking you to check for a short BETWEEN the gates of the two FETs (elswhere in the circuit).