Dell Q14228W 0.8 sec to black

[senderj]

Thank you for the "2 sec to black" post which encourage me to fix my failed mon. Very old (2007) Dell model but the layout is very similar to other Dell in this site. It works for <1 sec and than black. Re-power it gives me another <1 sec and black again. But shining a light on the screen doesn't seems to show any image of the display, not even the OSD. Without connecting to other board, just power up the psu and checked the psu board all +5V and +12V are working when without loading, but there is no high voltage from the inverters.

I have a few questions about the post. I would ask them in the sequence of the attempts that I would try to fix it.

1. Whole recap: while the caps look good but will do this, afterall, it is a 7 years old mon. But at the same time I would like to know which one causes the problem. I labelled the caps in the pic and hope that somebody could tell me what sequence should I replace them so that I can locate the fault faster.

2. Transformer: there is not label on the transformer. How do I find the right replacement? Can I simply rely on size and resistance?

3. CCFL: is physical size the only spec required to find a replacement? Read other post and people seems just find one from other mon and put it in.

Any other advises would be much appreciated. Please help.

[budm]

Re: Dell Q14228W 0.8 sec to black

First, I hope you are not trying to measure the high voltage out on the lamp connectors, you will damage the meter.
To save troubleshooting times, you should build two test lamps to help you narrow down the problem. You can solder the test lamp wires directly to the solder pads of the lamp connectors, you should have two lamps connected to each pair of the lamp connectors, then move to another pair if the lamps do not stay on.
https://www.badcaps.net/forum/showthread.php?t=19987
Also show the picture of the bottom side of the board, so we can trace the high voltage windings. You can try measuring the resistance between those two pins of the transformer which have the black thick circle around the pins.

[budm]

Re: Dell Q14228W 0.8 sec to black

BTW: here is the guide on 2-second to black:
https://www.badcaps.net/forum/showthread.php?t=10419

[senderj]

Re: Dell Q14228W 0.8 sec to black

Thanks. I read the guide before posting the questions.

These are the photos of the back side of the board.

I also measured the R of the transformers still on the board (with DMM at 2K/20M). Unlike most of the photos in this forum, the transformers only has 6 legs. Leg 1-4 at one side and 5-6 at the other.
All are open except
1-2 and 1-4 1M, 1-6 1K except T801 at 725 Ohm
2-4 shorted, 2-6 raising
4-6 risiing
I also have a photo on the label of the transformer 80GL20T-23-DN, but couldn't find in in eBay or lcdparts. There are ...-35-DN and ....-41-DN but the outlook is totally different. I don't know what spec I should loook for.

Will work on the lamps this weekend. Just to check my English. Am I right that I only need 2 lamps and I can test the upper 2 HV output first then the lower 2? The connector between the psu and the video board has a pin labelled "on/off". Does it means I need to connect them for the testing, not just the psu board? Please help.

[budm]

Re: Dell Q14228W 0.8 sec to black

OK, pin 6 and 1 is the high voltage winding, so the one that shows 725 Ohms should be removed and inspected.
You should also read this thread, your values are not the same, but the bottom line is that one of your transformer DC resistance is way off compared to the other transformers, the delta alone is showing that you do have transformer problem.

[senderj]

Re: Dell Q14228W 0.8 sec to black

If one transformer is down, I would assume 3/4 of the screen would still on. Doesn't it work this way?

[stj]

Re: Dell Q14228W 0.8 sec to black

if one transformer OR TUBE is bad the invertor will shutdown for safety reasons.

[senderj]

Re: Dell Q14228W 0.8 sec to black

OK. removed the transformer and measured the secondary to be 710 Ohm and primary 0.3 Ohm. Hunting for replacement. Will update. Thanks for all the help here.

[senderj]

Re: Dell Q14228W 0.8 sec to black

Not able to find this transformer. There are some close to it but the shipping is far more expensive. Ended up buying a replacement board. Checked the resistance of T801, 985 ohm, still lower than the other 997-1003 ohm. Put the board in and the mon lighted up again. Thank you all for your help to make it a success.