Testing a transformer

[stephkre]

Re: Testing a transformer

Here are some more pics.
I tested the transistors. Tell me if this is correct I turned my digital multimeter to the diode sign (the one with the arrow) and I measured my
1+2 .854V on Q6 .854V on Q5 when pos. terminal was on 1 (1 being the leg to the left when looking at the back three legs). The other way they would rise all the way until I got a 0L on my meter.
1+3 .667V on Q6 .667V on Q5 stayed steady. switched leads measured both at .603V.
2+3 both measured .281V when pos. terminal was on 3 and went to 0L when terminals where switched.
Does this mean they are good or bad.

[ratdude747]

Re: Testing a transformer

your board looks burnt

maybe thats a hint that you overheated somthing

[Bobdee]

Re: Testing a transformer

Here are some more pics.
I tested the transistors. Tell me if this is correct I turned my digital multimeter to the diode sign (the one with the arrow) and I measured my
1+2 .854V on Q6 .854V on Q5 when pos. terminal was on 1 (1 being the leg to the left when looking at the back three legs). The other way they would rise all the way until I got a 0L on my meter.
1+3 .667V on Q6 .667V on Q5 stayed steady. switched leads measured both at .603V.
2+3 both measured .281V when pos. terminal was on 3 and went to 0L when terminals where switched.
Does this mean they are good or bad.

You can take those readings as good because as I mentioned before one had to be working for backlights to come on for the 2sec on power up, so as they read the same that says they are both good
I am now suspicious of those CCFLs but before going there I think you should check your solder joints with about a 10 x magnifiying glass looking for bad solder joints and ring cracks, pay paticular attention to the Inverter transformers, if you find anything resolder all the joints on transformers, also check the 2 transistors that you just measured and those jumpers JP7+8 then have a browse over all solder
Then it would be worth trying again if you find any bad solder joints
BTW so there is no confusion for newbies those readings you made are OHMs not volts
bob

[stephkre]

Re: Testing a transformer

Ok I havent looked at my solder joints yet but I will do that when I get home. I was wondering if you could give me information on how to check if my CCFL tubes are the problem. Is there a way to check if the tubes are causing it? Thank You.

[stephkre]

Re: Testing a transformer

I just resoldered my joints and the monitor still shuts off. So I opened my lcd screen and pulled out the ccfl tubes it looks as though they are the problem. One set shows a reddish tent which I read means they are going out. The other set has one half shining and the other one dead. Now can anyone tell me where I can find the best deal for these tubes. I dont know what amperage they are all I know is they are 42 cm.
thank you

[Bobdee]

Re: Testing a transformer

I just resoldered my joints and the monitor still shuts off. So I opened my lcd screen and pulled out the ccfl tubes it looks as though they are the problem. One set shows a reddish tent which I read means they are going out. The other set has one half shining and the other one dead. Now can anyone tell me where I can find the best deal for these tubes. I dont know what amperage they are all I know is they are 42 cm.
thank you

Nice one
the reddish ones are on there way out so it may pay to replace the four,
Here is a link that gives another link to where you can buy them,
dont know if they are cheapest thou
https://www.badcaps.net/forum/showpo...5&postcount=57
bob

[PlainBill]

Re: Testing a transformer

I just resoldered my joints and the monitor still shuts off. So I opened my lcd screen and pulled out the ccfl tubes it looks as though they are the problem. One set shows a reddish tent which I read means they are going out. The other set has one half shining and the other one dead. Now can anyone tell me where I can find the best deal for these tubes. I dont know what amperage they are all I know is they are 42 cm.
thank you

That is very significant. It sounds like the output of one side of the inverter is low. Swap connections at the inverter to see if it's the set of CCFLs or the inverter.

PlainBill

[stephkre]

Re: Testing a transformer

One of the ccfl tubes was broken on the side that had one half glowing and the other dead. The glass seems to have came loose from the connection.

[stephkre]

Re: Testing a transformer

Does anyone know where I can find ccfl tubes that are 2 mm X 415mm I cant seem to find any.
Thanks

[PlainBill]

Re: Testing a transformer

Does anyone know where I can find ccfl tubes that are 2 mm X 415mm I cant seem to find any.
Thanks

How sure are you about the diameter? I've had problems getting a consistent measurement when I've tried. This could be either a problem with the gauge or the user - which works out to the same thing.

In any case, the best source I've found for CCFLs seems to be this guy. http://stores.ebay.com/Laptop-LCD-Parts-Direct (check out his auctions). Caveat - I have never purchased anything from him.

PlainBill

[kc8adu]

Re: Testing a transformer

i have 2 proview here with bad cffl's
2.2mm x 413?
i need to find my good ruler to double check.
dia is 2.2 for sure.

[EGuevarae]

Re: Testing a transformer

i have 2 proview here with bad cffl's
2.2mm x 413?
i need to find my good ruler to double check.
dia is 2.2 for sure.

I will go for 413 ones. 2mm short is nothing, but 2mm longer and you'll have problems getting the panel back together.

[stephkre]

Re: Testing a transformer

I got my ccfl tubes in and replaced my old ones and now it is working great thank you everyone. It was a pain in the butt replacing the ccfl tubes but I got it done.

[PlainBill]

Re: Testing a transformer

I got my ccfl tubes in and replaced my old ones and now it is working great thank you everyone. It was a pain in the butt replacing the ccfl tubes but I got it done.

Congratulations.

PlainBill

[EGuevarae]

Re: Testing a transformer

I got my ccfl tubes in and replaced my old ones and now it is working great thank you everyone. It was a pain in the butt replacing the ccfl tubes but I got it done.

Great. It feels good to bring a unit back from the death, right?

[tglenchur]

Re: Testing a transformer

Please help.

After replacing bad capacitors and failing CCFL's, my LT1919WDB has suffered a relapse during a local lightning storm surge. It was on a surge suppressor but the surge was enough to require rebooting my computer. The computer was OK. But the monitor was rendered unresponsive to the power button.

I've checked diodes and such but haven't found anything to explain or fix. I did check D203 out of circuit, after a suspicious in-circuit reading; but it seems fine. Large fuses and some the small SMD fuse are still conductive.

I attach the power and control board photographs with hope that you might have some helpful suggestions. Is there anything else to check?

[tglenchur]

Re: Testing a transformer

Hi,

I think the fault might be on the power/inverter board because after applying AC through the three prong connection, the ten-pin connector between the two boards reads zero volts among all the pins. At this point, are there any suggestions? TIA.

[tglenchur]

Re: Testing a transformer

Hi,

I missed a slow-blow T3 15A fuse that was open. I didn't know they could look like little terra-cotta colored blocks. I will update if a replacement is found and works. I feel like such a fool.

[PlainBill]

Re: Testing a transformer

Hi,

I think the fault might be on the power/inverter board because after applying AC through the three prong connection, the ten-pin connector between the two boards reads zero volts among all the pins. At this point, are there any suggestions? TIA.

Yes, we are going to use a technique I call 'Divide and conquer'. Since you provided a good picture of the bottom of the power supply / inverter board in it's shield, we will start there.

Step 1. Referring to the picture, plug in the power cord, and measure the voltage across C201 (upper edge of board, just to the right of center). It should read about 1.4 times your line voltage.

Step 1A. If the voltage was correct, measure the voltages at all 8 pins of IC201 (just to the right of C201). I believe pin 1 is in the lower right corner of the IC, the pins are numbered counterclockwise so pin 8 is on the lower left. Also, what is the part number on IC 201. Go to step 2.

Stem 1B. If you read 0 Volts across C201, unplug the power cord. Switch to the ohms scale, and measure the resistance across F201. It is the red 'box' mounted diagonally just to the left of the power cord receptacle. If it reads 0 ohms, go to step 1B1.

We have to determine why the fuse blew. Measure the resistance on BD201. It is the 4 pins in a straight line just to the left of C201. Pin 4 is at the top, pin 1 at the bottom. Measure the following resistances: 1-2, 1-3, 1-4, 2-3, 2-4, 3-4. If any pins read less than 10 ohms, they are shorted. If they read greater than 1Kohm, they are good. A reading which starts low, then increases to over 1K is considered good. If there is a short between any pins, what is the part number on BD201? Go to step 2.

The bridge rectifier was good. Now we check the power FET. It is Q201, just below IC201. It has three legs with a slot cut in the circuit board between pin 2 and the other two pins. Measure the following resistances: 1-2, 1-3, 2-3. If there are no shorts, go to step 2. If any pins are shorted, what is the part number of Q201? Go to step 2.

Step 1B1. You are not getting power, but the fuse is good. Unplug the power cord from the wall, plug it into the power receptacle on the power supply / inverter board. With the ohmmeter set on a low ohms scale, hold one probe on one flat prong of the power plug. You should get continuity to one side terminal of the power receptacle. If you don't try the other side terminal.

For the left side terminal, continue checking continuity through the jumper to the left, through the fuse, back to the right, through the second jumper, through one side of NF201 (squiggly line) through one side of NF201 (second squiggly line), through NTC201, and up to pin 2 of BD201

Now start at the OTHER flat prong of the power plug and check continuity to the right side contact of the power receptacle, through the other side of NF201, the other side of NF202, and to pin 3 of BD201

Where did you lose continuity?

Step 2. Report the results you found, then relax with the beverage of your choice.

PlainBill

[PlainBill]

Re: Testing a transformer

ARRGGGHHH!!!!

Better check WHY the fuse blew. See above post.

PlainBill