KDS K717 Turns on, flickers, then dies

[naterose77]

I have a KDS k717 LCD. It will turn on and work for about 1 minute. It starts to flicker and then the screen goes black. The power light is still green. I can power off and on and the image will appear again for around 5 seconds before the backlight goes dark again. I disassembled the LCD and looked for any signs of bulging capacitors. I wasn't able to find one. I am attaching pictures of the power supply and inverter boards. I was able to repair my viewsonic thanks to the advice on this forum and was hoping to fix this one as well.

Thank you for any help you can give.

[retiredcaps]

Re: KDS K717 Turns on, flickers, then dies

I have a KDS k717 LCD. It will turn on and work for about 1 minute.

A few suggestions.

1) It could be a poor solder joint somewhere.

2) One or more of CCFLs are slowing dying. As the CCFL age, they draw more power. If you see any pink or redish hues, that is a sign that your CCFLs are dying.

I have a LCD that has the similar symptoms with shutting down after some time and I have narrowed it down to the CCFLs.

3) See if your monitor stays on longer by lowering the brightness and contrast to 40/20. Usually most monitors are at 90/30 for the settings.

4) See if a cooling fan point at the back of the unit makes the LCD stay on longer.

[Rtech]

Re: KDS K717 Turns on, flickers, then dies

The PCB is very like the one used in Proview 700P and 900P monitors, as well as others.
One of the standard faults with those, is failure of one or both of the capacitors next to the output transformers,and in all cases I have seen,although they regularly fail, they never bulge,and you must measure ESR with them out of the Board, due to where they are in the circuit.The latter would be my first task.If you do not have an ESR meter, then would change them anyway and see if that fixes your problem.

[jetadm123]

Re: KDS K717 Turns on, flickers, then dies

Hello! Your board looks very similar to the board used on a Mag Innovision LT916s manufactured by Mirage Electronics. There's quite a lengthy thread here:

https://www.badcaps.net/forum/showthread.php?t=5220

Like Rtech said, it could be caps c10 and c11 that are causing your problem. Are they 100uf? Who are the caps made by? If they are all made by the same company you might consider replacing them all except fot the large 400-450V cap. Should cost under $10 (including shipping) if you order from digikey.com. I recommend Pansonic FM or FC series. Select USPS First Class shipping for lowest rate.

[naterose77]

Re: KDS K717 Turns on, flickers, then dies

A few suggestions.

1) It could be a poor solder joint somewhere.

2) One or more of CCFLs are slowing dying. As the CCFL age, they draw more power. If you see any pink or redish hues, that is a sign that your CCFLs are dying.

I have a LCD that has the similar symptoms with shutting down after some time and I have narrowed it down to the CCFLs.

3) See if your monitor stays on longer by lowering the brightness and contrast to 40/20. Usually most monitors are at 90/30 for the settings.

4) See if a cooling fan point at the back of the unit makes the LCD stay on longer.

1) That is entirely possible
2) The color of the screen was normal. There were no hues.
3) I tried reducing the brightness and there was no change. the flicker persisted until the screen went black.
4) I didn't think about heat issues. What are the chances of discharging a capacitor into my finger while feeling around on them after i unplug the monitor?

[naterose77]

Re: KDS K717 Turns on, flickers, then dies

The PCB is very like the one used in Proview 700P and 900P monitors, as well as others.
One of the standard faults with those, is failure of one or both of the capacitors next to the output transformers,and in all cases I have seen,although they regularly fail, they never bulge,and you must measure ESR with them out of the Board, due to where they are in the circuit.The latter would be my first task.If you do not have an ESR meter, then would change them anyway and see if that fixes your problem.

I don't have an ESR meter. I only have a digital multimeter. I think I'll the sizes off of them when i get off work tonight and order a whole new set.

[naterose77]

Re: KDS K717 Turns on, flickers, then dies

I found all the sizes of the caps on this board. They are all HEC brand rated at 105 degrees. I saw this brand on the bad brands list on this forum. I am attaching the picture with colored circles around each. the key is as follows

red: 25v 220 uF
yellow: 25v 470 uF
orange: 25v 680 uF

what is a good ripple current value for these? I looked these specs up on digikey and i'm not sure which ripple current mA to get. Can someone point me in the right direction? (the 680 only has one choice, 1.22A but the others range from mA to A)

[Wrog]

Re: KDS K717 Turns on, flickers, then dies

I found all the sizes of the caps on this board. They are all HEC brand rated at 105 degrees. I saw this brand on the bad brands list on this forum. I am attaching the picture with colored circles around each. the key is as follows

red: 25v 220 uF
yellow: 25v 470 uF
orange: 25v 680 uF

what is a good ripple current value for these? I looked these specs up on digikey and i'm not sure which ripple current mA to get. Can someone point me in the right direction? (the 680 only has one choice, 1.22A but the others range from mA to A)

In order to match up ripple, you would need to provide the series of the HEC brand caps so that the specs can be looked up. Usually this is a two or three letter code on the cap itself.

[retiredcaps]

Re: KDS K717 Turns on, flickers, then dies

Can someone point me in the right direction?

If you really want to know more about how to compare HEC and Panasonic, see

https://www.badcaps.net/forum/showpo...47&postcount=3

Follow PlainBill's instructions on how to order caps

https://www.badcaps.net/forum/showpo...33&postcount=2

The Panasonic FM or FC series as described in the URL above will work fine with the KDS.

[naterose77]

Re: KDS K717 Turns on, flickers, then dies

Here is all the info I was able to read off the caps. Thought i was going to have to desolder a couple at first.

HEC 25v 220 uF ZP 105° CU

HEC 25v 470 uF CU28 105°

HEC 25v 680 uF CU28 105°

Where can i find the ripple for these series so i can make sure Panasonic's FM are high enough?

[naterose77]

Re: KDS K717 Turns on, flickers, then dies

digikey has fast shipping. i opted for the cheaper first class mail and my new panasonic caps arrived today. i will put them in when i get home from work.

[naterose77]

Re: KDS K717 Turns on, flickers, then dies

I replaced all nine capacitors on the power supply board with panasonic CF's. the same problem still persists. it will power on initially and run fine for about a minute. then it flickers and the backlight goes out. the power light is still green. if i cycle power or plug/unplug the vga cable from the pc, the backlight comes back on for a couple of seconds before dying again.

any suggestions?

[Rtech]

Re: KDS K717 Turns on, flickers, then dies

The next thing to eliminate are the Backlights themselves,and to do that you really need a spare one,to substitute in turn for your own ones in the screen.You can soon determine which if any is faulty.

[jetadm123]

Re: KDS K717 Turns on, flickers, then dies

I replaced all nine capacitors on the power supply board with panasonic CF's. the same problem still persists. it will power on initially and run fine for about a minute. then it flickers and the backlight goes out. the power light is still green. if i cycle power or plug/unplug the vga cable from the pc, the backlight comes back on for a couple of seconds before dying again.

any suggestions?

I take it that if you let the monitor cool down for 15-30 minutes, then turn it on again, it will run for a minute, then flicker? Maybe a heat related problem? Maybe you can use a preheated blow dryer to accelerate the process to try and isolate the area that causing the shutdown. When you first turn on the monitor, blow one area continously to see if it causes problems. If not, after cool down repeat process in a different area.

[retiredcaps]

Re: KDS K717 Turns on, flickers, then dies

Maybe you can use a preheated blow dryer to accelerate the process to try and isolate the area that causing the shutdown.

The opposite approach is to take the cover off, shields off, and run it with a fan blowing directly across the boards and seeing if it stays on for more than 1 minute. If it stays on for 5 minutes, I would suspect the transistors on the backside of the board next to the transformers. I would resolder them.

You can see a bit of browning on the PCB board on the front next to the transformers. If this board is RoHS lead free, I would check all the soldering.

BTW, you haven't posted pictures of the backside. Some sharped eyed readers might be able to spot poor solder joints IF you provide sharp clear in focus pictures.

[naterose77]

Re: KDS K717 Turns on, flickers, then dies

i will find the 10MP kodak tomorrow and try to get some close-ups of the solder on the back that aren't blurry. Thanks for the advice. I will have to figure out a way to extend the wires or run both the ps and inverter cards sitting on the table with the screen held above them. there's not a lot of room to work with.

[retiredcaps]

Re: KDS K717 Turns on, flickers, then dies

I will have to figure out a way to extend the wires or run both the ps and inverter cards sitting on the table with the screen held above them. there's not a lot of room to work with.

If I wasn't clear, I mean reassemble your monitor with screws in, everything in its place, etc. Just don't put the back cover on so that the fan can blow across the components to keep them cool. You just need to run it for about 5 minutes to verify it is a temperature problem.

See this youtube video ...

http://www.youtube.com/watch?v=rePrm...eature=related

[Rtech]

Re: KDS K717 Turns on, flickers, then dies

Although all the suggestions have a lot of merit,UNLESS you eliminate the CCFL's as the problem,you are maybe chasing shadows.

[PlainBill]

Re: KDS K717 Turns on, flickers, then dies

Although all the suggestions have a lot of merit,UNLESS you eliminate the CCFL's as the problem,you are maybe chasing shadows.

I agree. There are two possible scenarios here. One is that there is a thermal problem, either the power supply, or the logic card. This includes either a chip overheating, or a bad solderjoint opening as it heats up.

The second scenario is you have one or more CCFLs that are drawing too much or too little current. It takes a minute or more to reach the point where it trips the protection circuitry on the inverter. That flickering certainly points to the second scenario.

A quick way to a solution is figuring out if the problem is a CCFL acting up and triggering the shutdown, or an interruption in the circuit powering the CCFL.

PlainBill

[retiredcaps]

Re: KDS K717 Turns on, flickers, then dies

Although all the suggestions have a lot of merit,UNLESS you eliminate the CCFL's as the problem,you are maybe chasing shadows.

The only reason I suggested the cooling first is that it seems that many members don't have a spare ccfl lying around for test purposes.

Especially if these members are not in the industry where they have piles of spare equipment on hand.