Samsung Model 731N No Display

[browork]

I have a Samsung Model 731N with No Display.

The power light does come on, green (does not go to amber).

No matter if a computer is plugged into the monitor the Green power light flashes (it stays on about 1 to 1.5 seconds, then goes off and immediately comes back on to repeat the cycle), but there is no display.

I am open to any ideas you may have.

Attached is pictures of the PSU.

[Wrog]

Re: Samsung Model 731N No Display

I have a Samsung Model 731N with No Display.

The power light does come on, green (does not go to amber).

No matter if a computer is plugged into the monitor the Green power light flashes (it stays on about 1 to 1.5 seconds, then goes off and immediately comes back on to repeat the cycle), but there is no display.

I am open to any ideas you may have.

Attached is pictures of the PSU.

Couple of quick things (going to try to sneak this reply in before PB gets here!):

1. Search for some of PlainBill's past posts for a problem called "two seconds to black"; there are a few common solutions that take care of the majority of these occurrences (transformers, inverters, CCFL wiring). These tests have been described in great detail in many other posts.

2. Take pictures with a little more detail. Here's a link to using macro mode for your camera: Photosmart M627 macro mode

[browork]

Re: Samsung Model 731N No Display

Sorry about the pictures. I take the pictures at 3040 x 2288, but have to resize them (down to 2000 x whatever) to post them. I had previously been working on some small pictures and only saving them 25% Quality for web page work. So when I did these I forget to change the settings. Either way I took a few more pictures and they are below. Much better quality as you can probably tell.

As for the "two seconds to black," I assume you mean the screen display. Nothing displays on my screen, only the power light flashes every few seconds. I will however still check them out. I was at a loss because this is the first model 731N on the forums and the 740N has a different PSU. I'm willing to try anything out that may help. Thanks for the quick reply.

[Wrog]

Re: Samsung Model 731N No Display

Sorry about the pictures. I take the pictures at 3040 x 2288, but have to resize them (down to 2000 x whatever) to post them. I had previously been working on some small pictures and only saving them 25% Quality for web page work. So when I did these I forget to change the settings. Either way I took a few more pictures and they are below. Much better quality as you can probably tell.

As for the "two seconds to black," I assume you mean the screen display. Nothing displays on my screen, only the power light flashes every few seconds. I will however still check them out. I was at a loss because this is the first model 731N on the forums and the 740N has a different PSU. I'm willing to try anything out that may help. Thanks for the quick reply.

Apologies, I mis-read the original post about the power light coming on versus the screen.

Have you replaced any caps or taken any measurements yet? Do you have test equipment handy (VOM or DMM)? Unless you've been able to troubleshoot and isolate a problem with particular component(s), generally the first step is to replace all of the electrolytic caps. Check for open fuses as well.

[MDOC]

Re: Samsung Model 731N No Display

I'd be interested in looking at this part (see circle). What's the part number?

But I'd start first with the fuses, and if OK, then replace all the Su'scon caps.

[browork]

Re: Samsung Model 731N No Display

Basically all I have is a DMM. I have other test equipment I inherited from a closed TV repair shop, but that stuff is in storage, uncalibrated and in unknown condition.

I do get a power light, but I tested the fuse anyway. It tests good.

The only other thing I can identify for sure is the Bridge Rectifier. As best as I can tell it tests good.

One thing PB mentioned in another post was to test the voltage at the big cap, saying it should be about 3x Voltage DC of my input (120V). Either that does not apply here or I am doing something wrong because I get nothing at that cap.

You say to replace the caps, that will take awhile as I live in the middle of nowhere Kansas. They look fine with no bulging that I can see above or below them.

Also when replacing the caps, you have the four brown ones, four small black ones, and one big blue one. Do you want all nine replaced?

Is there other things to look at while I wait for those parts to arrive?

I can follow instruction well and I am a good solderer, but I am truly a newbie when it comes to component level troubleshooting.

Attached is a better picture of that component you mentioned.

[PlainBill]

Re: Samsung Model 731N No Display

A couple of points pop up.

First of all, I'm concerned about the lack of a reading across the large cap. This should be 1.4 times your line voltage, or about 165 Volts DC.

Second, there is a multi-colored cable running to the logic card. There is a legend identifying the voltages on that cable. Check the readings from the Gnd pins to the other pins.

As far as replacement caps; if the voltage reading across the large cap is correct, I wouldn't replace it at this time. Definitely replace the other 8. Post the values, voltage, and dimensions of the existing caps if you would like help identifying replacements.

An excellent source of these caps is Digikey in Thief River Falls, MN. I won't say they are as isolated as you are, but they claim that on clear winter nights they look south to see the Northern Lights. Choose the First Class Mail shipping option for a fast (2 days), inexpensive (under $2.50) delivery.

One other thing to do is to post pictures of the logic card. Your symptoms sound like they might be due to a problem there.

PlainBill

[MDOC]

Re: Samsung Model 731N No Display

With the power to the monitor turned OFF, place a screwdriver blade across the cap leads momentarily to short out the cap. Then measure the big cap again, with the DMM set to measure ohms. If showing zero, you may have a shorted cap.

Yes, replace them all, because as I understand, those Su'scon caps are inferior caps even though nothing is physically wrong with them. I fixed a monitor recently by replacing caps that look perfectly good. Generally, if one cap is bad, you replace them all.

[browork]

Re: Samsung Model 731N No Display

Maybe I was on the wrong voltage level before. Or maybe shorting the cap out first did the trick.

I read 160.8V DC across the big cap now. So that should be good.


On the cable that runs to the logic card.

3/6 is ground
1/2 read 4.8V (board says 5V) so I guess thats good
4/5 read 0V (on/off and brightness) no clue if they should read anything
(the LCD is not currently connected if that matters)


As for the caps on the PSU...

1x Big Blue is 82uF 450V
4x Small Blacks are 47uF 25V
2x Small Browns are 470uF 25V
1x Med Brown is 1000uF 10V
1x Large Brown is 1000uF 25V


Caps on the Logic Board...

All Black, All Su'scon
1x 220uF 16V
2x 10uF 25V
5x 22uF 16V
2x 100uF 16V


Attached is pictures of the Logic Board

[MDOC]

Re: Samsung Model 731N No Display

Maybe I was on the wrong voltage level before. Or maybe shorting the cap out first did the trick.

Actually it's probably the former

I read 160.8V DC across the big cap now. So that should be good.

Yep...

[browork]

Re: Samsung Model 731N No Display

Actually it's probably the former Yep...

Hey, I can pretend I didn't mess up. Even if I do it only in my head.


I just noticed you asked for the dimensions of the Caps as well. Well I can give you my best guess based upon my standard first grade ruler. I probably have something more precise around here somewhere, but that will take digging. Either way both will wait until tomorrow, or later today now... I need sleep.

[MDOC]

Re: Samsung Model 731N No Display

No problem. Best tool to use is the dial (or digital) calipers, if you have them. McMaster Carr probably has them (I haven't checked, but I think they do).

[browork]

Re: Samsung Model 731N No Display

Yes caliper is what they are called. I think I have one in my toolbox, I'll just have to dig it up from the garage. I am fairly certain it is not digital though. It will be after I get back from town though.

Is there anything else I can check in the meantime?

[PlainBill]

Re: Samsung Model 731N No Display

Maybe I was on the wrong voltage level before. Or maybe shorting the cap out first did the trick.

I read 160.8V DC across the big cap now. So that should be good.


On the cable that runs to the logic card.

3/6 is ground
1/2 read 4.8V (board says 5V) so I guess thats good
4/5 read 0V (on/off and brightness) no clue if they should read anything
(the LCD is not currently connected if that matters)

4.8 volts is a little low. That could be an indication of bad caps. There are a couple of additional things to check, also. I've circled two voltage regulators on the logic card. Measure the voltage on each of the pins to ground (I've identified a point in the lower right corner of the board). Also, what are the part numbers of these regulators?

PlainBill

[browork]

Re: Samsung Model 731N No Display

Quick question...

While digging for my caliper I found a box of caps...

What is on the PSU is...

4x 47uF 25V
2x 470uF 25V
1x 1000uF 10V
1x 1000uF 25V

I have...

2x 1000uF 35V
2x 470uF 35V
4x 47uF 35V

Would those work as replacements...
They are all the same size as the others (except the 1000uF 10V is smaller then the replacement 1000uF 35V).

BTW, I found my caliper, but it is digital and needs batteries so I'll run back into town this afternoon and pick some up.

[browork]

Re: Samsung Model 731N No Display

As for the two voltage regulators.

Lets call the upper right one Number 1 and lower left one Number 2.

Number 1
Labeled
Line 1 A1
Line 2 AS1117L-18
Line 3 B0552

Voltages
Pin 1 0V
Pin 2 4.02V (unlabeled)
Pin 3 5.06V
Pin 4 4.02V


Number 2
Labeled
Line 1 A1
Line 2 AS1117L-33
Line 3 B0637 38

Voltages
Pin 1 0V
Pin 2 3.28V (unlabeled)
Pin 3 5.07V
Pin 4 3.28V

All voltages were measured to ground, in the lower left on the Monitor plug.

What's next....

[browork]

Re: Samsung Model 731N No Display

4.8 volts is a little low. That could be an indication of bad caps. There are a couple of additional things to check, also. I've circled two voltage regulators on the logic card. Measure the voltage on each of the pins to ground (I've identified a point in the lower right corner of the board). Also, what are the part numbers of these regulators?

PlainBill

As a side note I am reading 5.07V on those pins today. Not sure why it's different.

[MDOC]

Re: Samsung Model 731N No Display

Quick question...


I have...

2x 1000uF 35V
2x 470uF 35V
4x 47uF 35V

Would those work as replacements...
They are all the same size as the others (except the 1000uF 10V is smaller then the replacement 1000uF 35V).

Yep. Except the bigger cap for the 1000uF 10V might not fit, but if it does, then no problem.

Edit: Who's the manufacturer of those caps?

[browork]

Re: Samsung Model 731N No Display

All of those but two are XICON. The other two are nichicon (two of the 47uF 35V).

Are they any good quality? They have probably been in storage since I left the military. I have some monster caps too with screw terminals. No clue what I would ever do with them, but I am a little bit of a pack rat. You never know when I might use something, so if it is new or good I keep it.

For the smaller ones I also have some elgen, rubycon, jamicon and others. When I say I found a box, I mean I found about 300 small caps in several models and sizes.

Edit: And they all should fit fine. The biggest one is the 1000uF 35V, which is the exact same size as the 1000uF 25V that it is replacing. The one with the only size difference is the 1000uF 10V, but it sits next to the 1000uF 25V so it should not be any issue.

[PlainBill]

Re: Samsung Model 731N No Display

As for the two voltage regulators.

Lets call the upper right one Number 1 and lower left one Number 2.

Number 1
Labeled
Line 1 A1
Line 2 AS1117L-18
Line 3 B0552

Voltages
Pin 1 0V
Pin 2 4.02V (unlabeled)
Pin 3 5.06V
Pin 4 4.02V


Number 2
Labeled
Line 1 A1
Line 2 AS1117L-33
Line 3 B0637 38

Voltages
Pin 1 0V
Pin 2 3.28V (unlabeled)
Pin 3 5.07V
Pin 4 3.28V

All voltages were measured to ground, in the lower left on the Monitor plug.

What's next....

Bad news. The AS1117L-xx chips are voltage regulators, supplying critical voltages to components on the logic board. The xx in the part number indicates the output voltage. -33 indicates 3.3 volts, -18 indicates 1.8 volts. Severach had encountered a similar problem in this thread. Note in that case the overvoltage had fried the video chip on his monitor. At this point I wouldn't bother replacing the caps. If a voltage regulator becomes available, I'd try it before replacing the caps. An equivalent part by STMicroelectronics (497-6868-1-ND) is available from Digikey (497-6868-1-ND) for $.75 each.

PlainBill