Planar PL1700-BK - backlights go out

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

If you haven't already try re soldering the inverter coil and anything else that's thru hole around J906
Al.

I could be totally off base, but I can't shake the feeling that this might still be possibly thermal related since the ccfl stay on as long as 30 seconds. Thermal could also mean possibly bad solder joints on the transformer, blue high voltage caps, and resistors R930 and R921.

PlainBill is the expert in the current sense circuitry area and that might be the next area to investigate.

[De3rcr]

Re: Planar PL1700-BK - backlights go out

If you haven't already try re soldering the inverter coil and anything else that's thru hole around J906
Al.

Already resoldered all the J connectors

I could be totally off base, but I can't shake the feeling that this might still be possibly thermal related since the ccfl stay on as long as 30 seconds. Thermal could also mean possibly bad solder joints on the transformer, blue high voltage caps, and resistors R930 and R921.

PlainBill is the expert in the current sense circuitry area and that might be the next area to investigate.

I will resolder the transformer and surrounding caps and resistors.
I gotta go out for a few hours, will report when done.

[PlainBill]

Re: Planar PL1700-BK - backlights go out

Already resoldered all the J connectors



I will resolder the transformer and surrounding caps and resistors.
I gotta go out for a few hours, will report when done.

Referring to the picture I attached to post #33, I was going to suggest resoldering every point above the yellow line, plus the three points I have circled in yellow below it.

Perhaps I wasn't clear. I'm interested in the relative brightness of a CCFL tested at each connector. If a CCFL is noticeably brighter at J905 and J906 than it is at J903 and J904, that is significant.

Retiredcaps, the 30 second delay before turning off is significant, but there are multiple possible causes. One LCD TV I dealt with had a history of running for several hours before the CCFLS went off. This time gradually reduced to less than a minute. While in my possession it once ran perfectly for about 10 minutes. Then would shut down within a second. The cause was a bad transformer.

The cause could also be a leaky diode in the voltage sense circuitry that eventually causes the OVP to shut the inverter down. As a matter of fact, the results of using substitute CCFLs would tend to suggest that as the probable cause.

One more thing to try. Trace pin 2 of U901 to a point where you can solder a jumper to it. Jumper it to ground. Test the monitor with all four CCFLs hooked up.

PlainBill

[De3rcr]

Re: Planar PL1700-BK - backlights go out

Referring to the picture I attached to post #33, I was going to suggest resoldering every point above the yellow line, plus the three points I have circled in yellow below it.

Perhaps I wasn't clear. I'm interested in the relative brightness of a CCFL tested at each connector. If a CCFL is noticeably brighter at J905 and J906 than it is at J903 and J904, that is significant.

Retiredcaps, the 30 second delay before turning off is significant, but there are multiple possible causes. One LCD TV I dealt with had a history of running for several hours before the CCFLS went off. This time gradually reduced to less than a minute. While in my possession it once ran perfectly for about 10 minutes. Then would shut down within a second. The cause was a bad transformer.

The cause could also be a leaky diode in the voltage sense circuitry that eventually causes the OVP to shut the inverter down. As a matter of fact, the results of using substitute CCFLs would tend to suggest that as the probable cause.

One more thing to try. Trace pin 2 of U901 to a point where you can solder a jumper to it. Jumper it to ground. Test the monitor with all four CCFLs hooked up.

PlainBill

Sorry Plainbill, I didn't mean to circumvent your diagnosis by using the other panel.
I did go back and test the other J connectors when trying each ccfl on at a time in J903, J905 and J906 they all came on dim, but when I did J904 one of the ccfl's went "2 secs to black"(the ccfl that in normally pluged into J906) and the other 3 were dim.
I'm going to resloder everything above your yellow line and check it.

[PlainBill]

Re: Planar PL1700-BK - backlights go out

Sorry Plainbill, I didn't mean to circumvent your diagnosis by using the other panel.
I did go back and test the other J connectors when trying each ccfl on at a time in J903, J905 and J906 they all came on dim, but when I did J904 one of the ccfl's went "2 secs to black"(the ccfl that in normally pluged into J906) and the other 3 were dim.
I'm going to resloder everything above your yellow line and check it.

Using the other panel was a good test, but it now seems to be confusing the results. The other panel resulted in '5 seconds to black'. That suggests a problem either with the inverter output, or the feedback circuitry. Three of four CCFLs in the original panel appearing dim, one giving 'two seconds to black' would indicate a problem with that CCFL!!!

PlainBill

[De3rcr]

Re: Planar PL1700-BK - backlights go out

Using the other panel was a good test, but it now seems to be confusing the results. The other panel resulted in '5 seconds to black'. That suggests a problem either with the inverter output, or the feedback circuitry. Three of four CCFLs in the original panel appearing dim, one giving 'two seconds to black' would indicate a problem with that CCFL!!!

PlainBill

It is confusing, I resoldered everything and I still get about 5 seconds to black. The thing is, is that ccfl only went 2 seconds to black in that 1 connector J904, it stayed on longer in the other connectors.
I noticed something on the board when I was resoldering, it's circled in red. There is some solder on that R811 resistor that is connected to a C811 capacitor.

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

and took apart the LG and hooked it up and the ccfl's shut off after about 5 secs. Transformer???

Since there is some confusion here, can you describe how you did the LG ccfl test?

Did you test one LG ccfl at a time to the Planar? Or did you test all 4 LG ccfl to the Planar?

Also, during the testing, did you have a computer hooked up to it?

[De3rcr]

Re: Planar PL1700-BK - backlights go out

Since there is some confusion here, can you describe how you did the LG ccfl test?

Did you test one LG ccfl at a time to the Planar? Or did you test all 4 LG ccfl to the Planar?

Also, during the testing, did you have a computer hooked up to it?

I only plugged the all 4 LG ccfl's into the Planar ps/inverter board, I had to keep the Planar logic board attached so it would turn on, did not have a computer hooked to the LG panel, I only saw the ccfl's come on for about 5 seconds then they shut off.

Here's a pic of the Planar

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

I only plugged the all 4 LG ccfl's into the Planar ps/inverter board, I had to keep the Planar logic board attached so it would turn on, did not have a computer hooked to the LG panel, I only saw the ccfl's come on for about 5 seconds then they shut off.

After you get done testing all of PlainBill's suggestions, can you retest with just one ccfl at a time following the instructions in section 5

https://www.badcaps.net/forum/showpo...1&postcount=14

For your situation, the LG would be the good/spare ccfl. Again, you don't have to remove the ccfl from the LG, just stretch the Planar ccfl cable to the LG. Please hookup a computer to the Planar so you can see a display.

[De3rcr]

Re: Planar PL1700-BK - backlights go out

After you get done testing all of PlainBill's suggestions, can you retest with just one ccfl at a time following the instructions in section 5

https://www.badcaps.net/forum/showpo...1&postcount=14

For your situation, the LG would be the good/spare ccfl. Again, you don't have to remove the ccfl from the LG, just stretch the Planar ccfl cable to the LG. Please hookup a computer to the Planar so you can see a display.

So swap it around and hook the Planar lcd panel to the LG?
I don't think I'm going to see any image because I 'm not going to have the ribbon cable from the Planar hooked to the LG panel

The only thing I haven't done of Plainbill's is to ground pin 2 on U901, to me it looks like it doesn't go anywhere.

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

So swap it around and hook the Planar lcd panel to the LG?
I don't think I'm going to see any image because I 'm not going to have the ribbon cable from the Planar hooked to the LG panel

Since the Planar is the one having the problem, we want to keep as much as the original Planar parts in the test loop as possible. Hope the following makes sense. If not, please ask.

LG = good/spare ccfl.

1) Connect a working computer to VGA port of Planar. Make sure the computer is on and it displays the wallpaper or your desktop. Turn off any screen saver/sleep mode on your computer.

2) TURN POWER OFF and unplug the Planar monitor and wait 1 minute

3) disconnect Planar J903 and plug in LG into J903, leave J904 into Planar ccfl #2, J905 into Planar ccfl #3, and J906 into Planar ccfl#4

4) plug in monitor and turn monitor on - note if "2 seconds to black" occurs - if all ccfls stay lit for more than 2 minutes, move on to the next test

5) TURN POWER OFF and unplug the Planar monitor and wait 1 minute

6) disconnect Planar J904 and plug in LG into J904, leave J903 into Planar ccfl #1, J905 into Planar ccfl #3, and J906 into Planar ccfl#4

7) plug in monitor and turn monitor on - note if "2 seconds to black" occurs - if all ccfls stay lit for more than 2 minutes, move on to the next test

8) TURN POWER OFF and unplug the Planar monitor and wait 1 minute

9) disconnect Planar J905 and plug in LG into J905, leave J903 into Planar ccfl #1, J904 into Planar ccfl #2, and J906 into Planar ccfl#4

10) plug in monitor and turn monitor on - note if "2 seconds to black" occurs -if all ccfls stay lit for more than 2 minutes, move on to the next test

11) TURN POWER OFF and unplug the Planar monitor and wait 1 minute

12) disconnect Planar J906 and plug in LG into J906, leave J903 into Planar ccfl #1, J904 into Planar ccfl #2, and J905 into Planar ccfl#3

13) plug in monitor and turn monitor on - note if "2 seconds to black" occurs - see if all ccfls stay lit for more than 2 minutes

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

If you already tested the procedure outlined in post #51, please retest it again (after the resoldering - something might have changed).

[De3rcr]

Re: Planar PL1700-BK - backlights go out

OK, I get it now.

[De3rcr]

Re: Planar PL1700-BK - backlights go out

If you already tested the procedure outlined in post #51, please retest it again (after the resoldering - something might have changed).

OK,
This is getting crazy, I followed post #51 rather then explain it I put it in a spreadsheet(attached).

The thing is that after I did the last 2 I put it back to normal it stayed on for 15 minutes(even heated it with a blow dryer while it was on) then I uplugged it and let it sit for 5 minutes then plugged it back in and it stayed on for about 5 minutes then the ccfl's shut off.

[alexanna]

Re: Planar PL1700-BK - backlights go out

Could this be a possibility?
This is what is I think maybe going on, If I understand things correctly this is like a series circuit, But this an AC voltage source so I am not sure if this correct way to explain it.
J905 bulb has a return wire that's just hanging on by a couple of strands of wire.
I am thinking the design of the inverter transformer circuitry allows more voltage available to overcome the added resistance when the ccfl is in one position, but when it's installed in the other connector there is less voltage available to properly light the ccfl causing shut down.
Please correct me if I am wrong.
Al.

[De3rcr]

Re: Planar PL1700-BK - backlights go out

I plugged the LG panel into the Planar inverter board and the ccfl's stayed on for 2 hours. So I took apart the Planer lcd panel and one of the ccfl's on the bottom had black ends.

Where's a good place to order new bulbs and should I replace both?

This will be my first time replacing ccfl's any advice? I'm getting better with my soldering so I think I can get the wires onto the bulbs.

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

So I took apart the Planer lcd panel and one of the ccfl's on the bottom had black ends.

Where's a good place to order new bulbs and should I replace both?

See this thread as it talks about a supplier ...

https://www.badcaps.net/forum/showth...lwarehouse.com

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

So I took apart the Planer lcd panel and one of the ccfl's on the bottom had black ends.

BTW, which J90 connector was that ccfl with the black ends connected to?

[PlainBill]

Re: Planar PL1700-BK - backlights go out

So swap it around and hook the Planar lcd panel to the LG?
I don't think I'm going to see any image because I 'm not going to have the ribbon cable from the Planar hooked to the LG panel

The only thing I haven't done of Plainbill's is to ground pin 2 on U901, to me it looks like it doesn't go anywhere.

Based on the latest results, that isn't necessary.

PlainBill

[De3rcr]

Re: Planar PL1700-BK - backlights go out

BTW, which J90 connector was that ccfl with the black ends connected to?

It was J905. The other bulb looks a little discolored, Should I replace both?