Planar PL1700-BK - backlights go out

[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

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

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.

[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

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

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

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.

[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.

[alexanna]

Re: Planar PL1700-BK - backlights go out

got through checking J906 and J903 and all 4 ccfl's were dim.

Then I saw this(I didn't think about this either DUH!!)


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

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

[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???

Transformer appears to be okay with the 581 ohms reading.

[De3rcr]

Re: Planar PL1700-BK - backlights go out

I'd say 5 seconds or less. You want to be able to say 'Bright', 'Dim', or 'none'. You still might get 'two seconds to black', the resistances are a little low (120K ohm would be better).

I'd say little chance of blowing the board. The Radio Shack resistors are underrated for this, they will get warm.

What I'm hoping is you will find one of the two sides will be noticeably dimmer for all CCFLs (bad transformer), OR one CCFL will be noticeably different (bad CCFL or wiring).

PlainBill

got through checking J906 and J903 and all 4 ccfl's were dim.

Then I saw this(I didn't think about this either DUH!!)

I don't know why it didn't click before, but the LG Flatron 1718S-BN that you repaired can be used as "good" ccfl.

You don't take out the ccfls in the LG. Just drag the LG LCD close enough to the Planar and stretch out the connector (don't let the two LCDs touch).

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

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

Unfortunately I don't have any spare parts to check the ccfl's.

I don't know why it didn't click before, but the LG Flatron 1718S-BN that you repaired can be used as "good" ccfl.

You don't take out the ccfls in the LG. Just drag the LG LCD close enough to the Planar and stretch out the connector (don't let the two LCDs touch).

[De3rcr]

Re: Planar PL1700-BK - backlights go out

I'd say 5 seconds or less. You want to be able to say 'Bright', 'Dim', or 'none'. You still might get 'two seconds to black', the resistances are a little low (120K ohm would be better).

I'd say little chance of blowing the board. The Radio Shack resistors are underrated for this, they will get warm.

What I'm hoping is you will find one of the two sides will be noticeably dimmer for all CCFLs (bad transformer), OR one CCFL will be noticeably different (bad CCFL or wiring).

PlainBill

Well, I put resistors across J903, J904 and j905 and tested J906 with the ccfl that was originally in J905 and it was dim, I left it on a little too long(15-20 secs) and smoked the resistor on J905, going to replace that and try again.

[PlainBill]

Re: Planar PL1700-BK - backlights go out

I got the resistors, you say a "short period" would that be about 30 seconds or less. I just want to make sure I don't fry this board.

I'd say 5 seconds or less. You want to be able to say 'Bright', 'Dim', or 'none'. You still might get 'two seconds to black', the resistances are a little low (120K ohm would be better).

I'd say little chance of blowing the board. The Radio Shack resistors are underrated for this, they will get warm.

What I'm hoping is you will find one of the two sides will be noticeably dimmer for all CCFLs (bad transformer), OR one CCFL will be noticeably different (bad CCFL or wiring).

PlainBill

[De3rcr]

Re: Planar PL1700-BK - backlights go out

This means that disconnecting one bulb of the pair is not a valid test UNLESS some provision is made to pass current through the open socket. The best way would be to use a resistor. Radio Shack 271-1131 is a 5-pack of 100K ohm .5 watt resistors. They should work FOR A SHORT PERIOD, and are normally stocked in the stores.

This is going to be crude, but what I would suggest is soldering one resistor across each unused socket (I've circled the pins of each socket in matching colors.), then plugging a CCFL into one socket, turning on the monitor briefly and evaluating how bright the CCFL lights. For the first test, I would suggest trying all four CCFLs in turn in the same socket. For the second test, I would suggest testing one CCFL at a time in each socket, with the other sockets jumpered by a resistor. Yes, this will require unsoldering and resoldering resistors. Be careful, the resistors may get hot.

PlainBill

I got the resistors, you say a "short period" would that be about 30 seconds or less. I just want to make sure I don't fry this board.

[PlainBill]

Re: Planar PL1700-BK - backlights go out

This inverter transformer uses a newer design. Early designs had one CCFL per transformer. One end of the secondary fed the CCFL, usually through a capacitor. The other end of the secondary was either tied to ground or to a current sensing circuit. Later designs coupled the output to two CCFLs by using two capacitors.

This design uses two CCFLs driven from opposite ends of the secondary windings. The return lines from the CCFLs either go to current sensing circuitry or to ground. There are usually a few capacitors to sense voltage, and to tune the circuit.

The best way I can illustrate the difference is the old way was like two flashlight batteries, each with a flashlight bulb connected to the top and bottom. In that design, each battery and bulb set is independent of the other.

The analogy for the newer design would be two batteries in series, and two light bulbs in series. and the light bulbs connected from the bottom of one battery to the top of the other. In this case, they are dependent on the other.

This means that disconnecting one bulb of the pair is not a valid test UNLESS some provision is made to pass current through the open socket. The best way would be to use a resistor. Radio Shack 271-1131 is a 5-pack of 100K ohm .5 watt resistors. They should work FOR A SHORT PERIOD, and are normally stocked in the stores.

This is going to be crude, but what I would suggest is soldering one resistor across each unused socket (I've circled the pins of each socket in matching colors.), then plugging a CCFL into one socket, turning on the monitor briefly and evaluating how bright the CCFL lights. For the first test, I would suggest trying all four CCFLs in turn in the same socket. For the second test, I would suggest testing one CCFL at a time in each socket, with the other sockets jumpered by a resistor. Yes, this will require unsoldering and resoldering resistors. Be careful, the resistors may get hot.

PlainBill

[smason]

Re: Planar PL1700-BK - backlights go out

Here I just finished shoveling snow and it is piled about 2 feet on one side. Anyone still playing Beach Volleyball on Daytona Beach?

You must be near me. I'm SO tired of shovelling already, and it's only November....

[De3rcr]

Re: Planar PL1700-BK - backlights go out

If you plug in the 3 other ccfls one at a time to the connector J906 that does not light the ccfl,
Do you still get no light, or do any of the other bulbs light up dimly?
Al.

no , the lights do not come on in J906, they light dim and then go out in J903

I also resoldered J906 and J903 same results

[alexanna]

Re: Planar PL1700-BK - backlights go out

OK,
Taking the middle lights and pluging them into the outer sockets, the left(J903) one came on really dim and then shut off and the right(J906) one didn't come on at all. I plugged the outer lights into the inner sockets and they came on bright and then shut off. So when the either light is plugged into the inner sockets(good ones I hope) they all come on bright and then shut off.

I didn't know you could switch the lights around like that(add that to my troubleshooting notebook).

If you plug in the 3 other ccfls one at a time to the connector J906 that does not light the ccfl,
Do you still get no light, or do any of the other bulbs light up dimly?
Al.

[retiredcaps]

Re: Planar PL1700-BK - backlights go out

Sorry,
J906 far right
J903 far left

Yes, and J903 comes on but not as bright as J904

I have to run off for about 5 hours, but try resoldering the 4 backside connectors on J906 and retest. If that doesn't work, then we will have to trace out J906 and see which component(s) is bad (on the backside).

The good news is that J905 is working so we have a known good circuit for comparison.