Noobie with Viewsonic N2750W Problem (2 Secs to Black)

[jrw8778]

Hi everyone!

My friend gave me a n2750w after a "computer guy" looked at it for him and told him it cannot be fixed.

It apparently has what you folks here dub the "two seconds to black" problem. It powers on OK, screen flashes up (for less than 2 seconds) and then the backlight turns off. The LCDs still work, if I move a mouse across the screen it is vaguely visible.

I just did a simple online search for the problem and discovered that bad electrolytic capacitors (whatever they are) may be the problem. I went to a third party vendor who sold me a kit that would replace the bulk of the capacitors on the power supply board. I examined the board prior to swapping out the capacitors and could not find any that were bulging, broken, askew or otherwise obviously bad. Nevertheless I changed out all the capacitors, with no results.

At this point I was going to next change the fuse (labeled T4AH250v), and that's when I discovered your forum. I read up a little here and decided to see if you can give me further advise.

Please keep in mind the level of my noobishness (I do not have a background in EE, I own a soldering iron but I do not own a multi-meter, I haven't had a math class in over 20 years). As far as the fuse goes, I've contacted numerous local TV / computer repair shops (believe it or not we do not have an electronics store in my beautiful burg) but none will sell me a replacement fuse. Can you folks recommend somewhere online I may find such a part? I believe it to be a time-lag 4 Amp 250v fuse, is that correct?

Although I would love for the fuse to fix the problem, I'm anticipating it will not, and thus I will be forced to move on to the next step. What do you experts recommend next?

Thanks for any response, really. I searched the forum and found the service guide for this model and have already downloaded it and I'll look through that today.

[PlainBill]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Hi everyone!

My friend gave me a n2750w after a "computer guy" looked at it for him and told him it cannot be fixed.

It apparently has what you folks here dub the "two seconds to black" problem. It powers on OK, screen flashes up (for less than 2 seconds) and then the backlight turns off. The LCDs still work, if I move a mouse across the screen it is vaguely visible.

I just did a simple online search for the problem and discovered that bad electrolytic capacitors (whatever they are) may be the problem. I went to a third party vendor who sold me a kit that would replace the bulk of the capacitors on the power supply board. I examined the board prior to swapping out the capacitors and could not find any that were bulging, broken, askew or otherwise obviously bad. Nevertheless I changed out all the capacitors, with no results.

At this point I was going to next change the fuse (labeled T4AH250v), and that's when I discovered your forum. I read up a little here and decided to see if you can give me further advise.

Please keep in mind the level of my noobishness (I do not have a background in EE, I own a soldering iron but I do not own a multi-meter, I haven't had a math class in over 20 years). As far as the fuse goes, I've contacted numerous local TV / computer repair shops (believe it or not we do not have an electronics store in my beautiful burg) but none will sell me a replacement fuse. Can you folks recommend somewhere online I may find such a part? I believe it to be a time-lag 4 Amp 250v fuse, is that correct?

Although I would love for the fuse to fix the problem, I'm anticipating it will not, and thus I will be forced to move on to the next step. What do you experts recommend next?

Thanks for any response, really. I searched the forum and found the service guide for this model and have already downloaded it and I'll look through that today.

I have several recommendations:

1. Don't bother replacing the fuse.

2. You WILL need a DMM. If you were going to work full time repairing electronics I would suggest you spend $200 or more on a Fluke. For what you are going to do, Harbor Freight #37772 or this DMM from (Faraday forgive me) Walmart makes more sense.

3. Even before you start shopping for a DMM, supplying a few pictures will help. I am particularly interested in one of the inverter.

PlainBill

[jrw8778]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Hi Bill, thanks for the response. I figured I'd need to upload some photos, but I wanted to make sure I uploaded the correct ones.

Here's a couple pictures of the Power Supply Board. I think I saw online that this model also has a backlight inverter, I don't think I've uncovered that board yet, so if that's what I need it's going to have to wait until tomorrow (when I will also get my multi-meter. I have high res originals, so if there's part you want to see in detail, I can get that for you.

[PlainBill]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Hi Bill, thanks for the response. I figured I'd need to upload some photos, but I wanted to make sure I uploaded the correct ones.

Here's a couple pictures of the Power Supply Board. I think I saw online that this model also has a backlight inverter, I don't think I've uncovered that board yet, so if that's what I need it's going to have to wait until tomorrow (when I will also get my multi-meter. I have high res originals, so if there's part you want to see in detail, I can get that for you.

Most of the testing will be on the inverter, so uncovering that will be useful.

PlainBill

[jrw8778]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Ok, folks. These are not perfect pictures. I see nothing obviously wrong (charring or burst / bulging capacitors). Any thoughts?

[jetadm123]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

What brand/series are those 8 green caps at the bottom of the board?

[PlainBill]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Ok, folks. These are not perfect pictures. I see nothing obviously wrong (charring or burst / bulging capacitors). Any thoughts?

Take a look at the first transformer. Note the white dot on the lower right corner. That is pin 1. Numbering goes counterclockwise, so the pin at the upper right corner is pin 4. Pin 5 is the top pin on the left, and pin 8 is the bottom pin on the left.

When you get your DMM, measure the resistance between pins 1 and 8, and between 4 and 5. Write down those numbers, you are going to need them. Do the same with the remaining transformers. Each reading should be about 980 ohms.

Now compare the readings. You are looking for an 'outlier' - a reading that is lower or higher than the rest. Report the readings.

PlainBill

[jrw8778]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

jetadm123: I will check the capacitor brand name when I get home and post it.

PlainBill: Should I remove the board prior to testing it with the DMM, will it matter if it's still connected to the TV?

Thanks again folks, I know it's a PITA to baby step a new guy through this stuff.

[jrw8778]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Ok. I went to Radio Shack and bought a cheap DMM. I got home and realized it had a billion settings, I knew Bill was looking for resistance so I set it to "200K" under the Ohm settings and started taking measurements. Here's the readings I got:

1. 1-8: 102.1. 4-5: 101.9
2. 1-8: 101.5. 4-5: 101.7
3. 1-8: 101.9. 4-5: 102.1
4. 1-8: 102.4. 4-5: 102.4
5. 1-8: 102.9. 4-5: 187.8
6. 1-8: 103.3. 4-5: 103.4
7. 1-8: 103.6. 4-5: 103.7

Obviously the outlier is the 4-5 pin on number 5. Unless my method of measurement was faulty. I checked it like 4 times because it was so far off. So, what do you guys think now?

Regarding the capacitors, they're very small and I'm having trouble reading them. I'll post as large a photo as I can of them in a bit.

[jetadm123]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Ok. I went to Radio Shack and bought a cheap DMM. I got home and realized it had a billion settings, I knew Bill was looking for resistance so I set it to "200K" under the Ohm settings and started taking measurements. Here's the readings I got:

1. 1-8: 102.1. 4-5: 101.9
2. 1-8: 101.5. 4-5: 101.7
3. 1-8: 101.9. 4-5: 102.1
4. 1-8: 102.4. 4-5: 102.4
5. 1-8: 102.9. 4-5: 187.8
6. 1-8: 103.3. 4-5: 103.4
7. 1-8: 103.6. 4-5: 103.7

Obviously the outlier is the 4-5 pin on number 5. Unless my method of measurement was faulty. I checked it like 4 times because it was so far off. So, what do you guys think now?

Regarding the capacitors, they're very small and I'm having trouble reading them. I'll post as large a photo as I can of them in a bit.

Looks like PlainBill made the right call. Transformer #5 looks way off with 188 ohms. Does the transformer have a part number stamped on it?

[jrw8778]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Looks like PlainBill made the right call. Transformer #5 looks way off with 188 ohms. Does the transformer have a part number stamped on it?

Yes, the part number is visible in the photos above (I think its the part number anyway):

4006A530 028 GP

Do I just need to find a replacement and solder it onto the board?

EDIT: Looks like any transformer labeled 4006A will work, correct?

[PlainBill]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Looks like PlainBill made the right call. Transformer #5 looks way off with 188 ohms. Does the transformer have a part number stamped on it?

The part number is visible in the first inverter picture; it is a 4006A. There are a number available on eBay; search for 4006A 070-001.

PlainBill

[jrw8778]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Thanks for the advice. I'd like to get this project wrapped up in the next few days. Would this part suffice:

http://www.lcdparts.net/TransformerD...ProductID=2749

Or am I better off ordering from somewhere in China. I really don't want to wait a month to get this done.

[jetadm123]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Funny, but if you search Ebay under N2750W, you'll find a seller selling the entire inverter board. Just verify it's the same model/revision number.

[jrw8778]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Wow, great find. If you look at my third picture of the inverter board you'll see it's the same as this one for sale. I'm going to get it...but let me ask a question: If this board fails for whatever reason, can I just use one of the transformers from this board and replace the faulty one on the board I have? Is that shady or "not recommended" or anything?

Also thanks to everyone for helping.

[jetadm123]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

No harm in swapping parts between boards, especially if the part is hard to find or obsolete. Just make sure it's the same part number.

[mh1723]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

I had to say thanks for all your help as well. I recently picked up a used N2750w as well with the same issue and this was insanely helpful. Many thanks to all!!!

Matt

[jwp616]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Hopefully someone from this thread is still paying attention and can help me. I came across this post because I am experiencing the same issue with the same TV. I have followed the discussion above and have the TV apart down to the inverter board. However, after using my multimeter on all the pin connections, I did not find one that was out of line. They all came in very close to 1000 ohms give or take a needle width or two on my meter.

Since none of the pins seem to be outliers, would you still suggest replacing the inverter board or is there something else you would recommend trying to troubleshoot the issue?

[PlainBill]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Hopefully someone from this thread is still paying attention and can help me. I came across this post because I am experiencing the same issue with the same TV. I have followed the discussion above and have the TV apart down to the inverter board. However, after using my multimeter on all the pin connections, I did not find one that was out of line. They all came in very close to 1000 ohms give or take a needle width or two on my meter.

Since none of the pins seem to be outliers, would you still suggest replacing the inverter board or is there something else you would recommend trying to troubleshoot the issue?

First, many of us regulars scan new posts several times a day. Reopening an old thread is not a problem.

Next, an analog DMM may not have sufficient resolution to detect a bad transformer. I had one where the bad transformer was only off by 5% - right at the limit of an analog VOM.

Retiredcaps has written an excellent tutorial on troubleshooting 'Two seconds to black'.

PlainBill

[jwp616]

Re: Noobie with Viewsonic N2750W Problem (2 Secs to Black)

Thank you! Very helpful.