Samsung 266BW - blue power light stays off

[montreal]

Hello, this is my first post and any feedback on my problem will be greatly appreciated.

My neighbor gave me his 2 year old Samsung 226BW after it died completely on him a few months ago. Having been an electronics hobbiest for some time, I welcomed the chance to try to give it a new life.

I found that the monitor would have a black screen even though the blue power light was on.

If I disconnected the computer video cable (DVI) and left the monitor attached to the 120 volt AC, then after about 30 minutes I would finally get that moving message on the screen requesting an analog or digital connection. Once the video connection was made, then the monitor worked fine until it fell into Power Save mode and eventually cooled down.

Once cool, the monitor would not wake up and the blue light continued to flash. The screen would stay black. The blue power light eventually went off and would only come back on if I disconnected the video cable (DVI). Reconnecting the video cable would make the light go off again.

If I permanently disconnected the computer cable and plugged the monitor back into the 120 Volt AC source, then eventually it would warm up enough to work again.

Once I stopped using the Power Save option, the monitor continued to work OK in screen saver mode. I found that if I had to reboot the computer, my monitor was OK as long as I restarted everything quickly.

Last night I had to shut down the PC to clean the CPU fan. The delay getting the monitor back on-line was too long and this time, the monitor's blue power light never came back on.

So after discovering this web site, I opened up the monitor and determined that three 25 volt capacitors on the power supply board were bulging. I changed these 3 caps as well as 3 other 25 volt types which were not bulging.

Unfortunately that did not change anything for the better.

What I do know is that apart from producing the high voltage for the backlamp, the power supply board produces 14 volts DC for the display (logic) board.

From what I can tell, the logic board receives the 14 volts DC via a 9 wire flat cable and the logic board converts this 14 volts to a number of lower voltages including 1.8 volts, 3.3 volts, and 5 volts. The logic board sends 3 signals back to the power supply board (DimA, DimB, and ON/OFF). I conclude that the DimA/DimB signals tell the lamp's inverter to set the backlight level and the ON/OFF signal orders the lamp inverter to go into Power Save mode.

My problem is that I have no 5 volts appearing on the display logic board at any of the locations marked as 5 volt test points. The high voltage 170 volts DC, and 1.8 Volts DC and 3.3 Volts DC are all OK.

The 5 volts that the video board needs does not appear to be produced on the power supply board as is the case with other Samsung models.


So I would conclude that locating where the 5 volts is created on the video board might be the first step to solving my problem.

As well I am trying to discover where the actual blue power light comes from. When I disassemble the power switch, I see no additional blue LED.

Any advice?

Thanks

[Rtech]

Re: Samsung 266BW - blue power light stays off

Suggest you supply some photos,the method being described in many of Plain Bills entries,and you will probably get some help.

[PlainBill]

Re: Samsung 266BW - blue power light stays off

Retiredcaps must be taking the afternoon off. He's earned the break. Note the links in my signature. First, verify you used the proper caps. That's a common error.

Next, follow the links on taking pictures and take pictures of both the bottom and top of the power supply and the logic card. Attach them to your next post.

PlainBill

[montreal]

Re: Samsung 266BW - blue power light stays off

Thanks for your encouragement on my problem. Since posting, I have examined the video board and identified the DC to DC converter chip that transforms 14 VDC to 5VDC. Next week I will have a chance to see exactly where the 5 volts is not coming through.

As for the missing blue LED power light, there appears to be two surface mounted LED diodes the size of pin heads soldered to the small circuit board that carries the ON/OFF pushbutton. Much smaller than a typical LED, these compact structures are a minimalist solution.

I'll post followup reports next week. Happy labor day.....

[retiredcaps]

Re: Samsung 266BW - blue power light stays off

I'll post followup reports next week. Happy labor day.....

If "montreal" is actually a Canadian from Montreal, that person, like me today, is probably trying to enjoy what is left of summer here in Canada.

PS. Great detailed description of your problem. A refreshing change from some of the other recent posts.

[PlainBill]

Re: Samsung 266BW - blue power light stays off

If "montreal" is actually a Canadian from Montreal, that person, like me today, is probably trying to enjoy what is left of summer here in Canada.

Meanwhile, here in Phoenix we are hoping Summer relents enough to allow us to enjoy the Labor Day holiday. High today of 111°F, but only 102°F on Monday.

PlainBill

[smason]

Re: Samsung 266BW - blue power light stays off

If "montreal" is actually a Canadian from Montreal, that person, like me today, is probably trying to enjoy what is left of summer here in Canada.

PS. Great detailed description of your problem. A refreshing change from some of the other recent posts.

Summer? I think we missed it this year. 6 degrees C here, but might make 21 this afternoon.
That's 43F and 72F for you Americans.

[PlainBill]

Re: Samsung 266BW - blue power light stays off

Summer? I think we missed it this year. 6 degrees C here, but might make 21 this afternoon.
That's 43F and 72F for you Americans.

Those temperatures remind me of growing up in Minnesota. You know the climate - 9 months of Winter, three months of poor sledding.

PlainBill

[Wrog]

Re: Samsung 266BW - blue power light stays off

Those temperatures remind me of growing up in Minnesota. You know the climate - 9 months of Winter, three months of poor sledding.

PlainBill

Or like in Chicago, there's two seasons: winter and construction.

To the OP: Great details, but as PB always says: A picture is worth a thousand words! Hopefully you're able to provide them so that it will be easier to provide troubleshooting steps.

[montreal]

Re: Samsung 266BW - blue power light stays off

Suggest you supply some photos,the method being described in many of Plain Bills entries,and you will probably get some help.

Please note that my monitor is the 226BW, my typo incorrectly said 266BW.

Thanks for the prompt to post photos.

I took some photos today of the front side and rear side of both the power-inverter board and the video board.

After digging up some Samsung schematics for closely related monitors, I confirmed that the only voltage produced by the IP board is 14 volts DC and the video board is correctly generating the 5, 3.3 and 1.8 volts DC. All these voltages are available at the various test points on the video board.

I tested the voltage across the power-on button and it is OK (1.8 volts). As well the blue LED glows slightly if I feed it some current from my multimeter.

However I suspect that my main scaler chip on the video board (SE758MRH-LF) may not be working properly as it is failing to send more than 1.8 volts to the blue power-on LED. I think the LED needs a few more volts to turn on.

While I do have another schematic diagram for a similar monitor (the SE85AMH scaler chip also has 128 pins like my own chip), without the full board diagram identical to my video board, it is hard to trace any further.

So I think I may have to bite the bullet on this one and say that whatever is wrong with my monitor is much more complicated than replacing some bulging electrolytic capacitors, which I did anyway.

Thanks again for your participation in this thread.

[Solder Boy]

Re: Samsung 266BW - blue power light stays off

You may have other capacitors that are bad.. if you don't have an ESR meter then you won't have any idea. I'm finding with fixing LCD's that you start off with the easiest solutions first before you look for other culprits.

If you look at my thread re the LG Flatron Widescreen, I replaced the obvious bad caps and it still wouldn't turn on.. I have an ESR meter so I went hunting for other bad caps.. sure enough I found 2.. one was completely shot the other cap read 6 which is bad bad.

Having a capacitance meter would help too.. but depending how often you plan on doing this..might be hard to justify the cost.

As stated elsewhere the blue light gets its power from the logic board.. the logic board gets it's power from the inverter board. so if a cap is bad that will stop voltage.

Hope this helps.

[montreal]

Re: Samsung 266BW - blue power light stays off

You may have other capacitors that are bad.. if you don't have an ESR meter then you won't have any idea.........

......Having a capacitance meter would help too.. but depending how often you plan on doing this..might be hard to justify the cost............

As stated elsewhere the blue light gets its power from the logic board.. the logic board gets it's power from the inverter board. so if a cap is bad that will stop voltage.

Thanks Solder Boy for the reply.

My blue light gets its power from the logic board. It actually gets 1.8 volts directly from the scaler chip (pin number 123). The scaler chip is fed at many pins by two sources providing 1.8 and 3.3 volts. 1.8 volts is not enough to make the blue light glow. I suspect it needs closer to 3 Volts.

There are 6 push buttons on the front panel including the power-on switch. These buttons are connected to two quad state lines which connect directly to pins 119 and 120 of the same scaler chip. These two lines normally idle at 1.8 volts. Pressing any one of these 6 buttons will set the state on these two lines to 0.0, 0.5, and 1.0 volts. The scaler chip sees a unique combination of these levels on the two lines and then decodes what button must have been pushed. All my buttons appear to be generating the correct voltages when pushed.

So if my pressing of the power-on button does not cause my blue light to come on, it may be that the scaler chip is not cycling because the crystal clock is not generating the 14.31818 Mhz. frequency needed by the chip. However my scaler chip has nevertheless managed to turn off the BL-EN signal to the inverter and the PANEL_EN signal to the panel. To do this, the scaler chip had to set pin 109 to -0.2 volts and pin 3 to 1.72 volts. I believe this suggests that the scaler chip is functioning to some degree.

The only low voltage source on the IP board is 14 volts and I am reading 15 volts on my DVM. I have changed the axial caps (there were 4 caps in parallel for a total of 3X820 and 1X330 microfarads).

Let us assume that there is no ripple on the IP board and the logic board is receiving good quality 15 volts DC.

From the photos attached to my previous post, you can see that all caps on my logic board are surface mounted ones, most of them at 10 microfarads 16 volts. None are bulging. All have the proper voltage of 1.8, 3.3, 5, and 15 measured across them. Because I don't have an ESR nor a capacitor testing meter, I cannot speak for the quality of the voltage across each cap, only the quantity. Unlike the IP board, these caps which look a lot like TO5 transistors (top hats) run relatively cool as they don't handle a lot of power.

I am reluctant to unsolder any of these surface mounted caps and if I did, I would only have axial types available to substitute. I have not seen surface mounted caps sold in my local industrial electronics store.

What I need is a scope to see if I am getting some ripple across any of these caps.

Before my monitor completely failed, I already knew that chassis heat was a factor that sustained the operation of the monitor. It needed an hour plugged into the wall on its own before the pop-up message would appear on the screen requesting a connection to the PC. And it needed to be left with an image constantly on and not allowed to fall into power-save mode, else it would fail to come back on.

I will continue to investigate.

Has anyone ever changed a surface mounted cap on a logic board and found that doing so made the repair a success?

[montreal]

Re: Samsung 226BW - blue power light stays off

As a last effort before giving up, I temporarily soldered a 100 microfarad capacitor in parallel with each electrolytic cap on the logic board in order to provide extra filtering in case any one cap was marginal.

That did not improve things so I came to the conclusion that whatever is wrong with the logic board, it is probably within the scaler or one of the two eeproms or with the flash memory.

I could never find the perfect schematic for my particular version of the 226BW. The best I could do was find a diagram for the 206/226 general series and that was a poor match to my circuit board. It turns out that the 940BW diagram has more in common with my own board except that the IP board of the 940BW furnishes the 5 volts along with the 14 volts.

Since my monitor was built in October 2007, Samsung has agreed to honor the 3 year warranty and I will be shipping it to them in the next few days.

Even though I hit a dead end on the logic board in spite of the power supply caps being bad, I did learn a lot about the design of flat screen displays and that experience alone will help me to deal with any breakdowns which may occur with my future flat screen purchases.

Thanks again to all who helped me along on this problem.

[jetadm123]

Re: Samsung 226BW - blue power light stays off

Since my monitor was built in October 2007, Samsung has agreed to honor the 3 year warranty and I will be shipping it to them in the next few days.


Thanks again to all who helped me along on this problem.

Hopefully, you didn't void the warranty by opening it up and soldering the circuit boards. The company may use the excuse that you "tampered" with it and won't honor the warranty.

[montreal]

Re: Samsung 226BW - blue power light stays off

Hopefully, you didn't void the warranty by opening it up and soldering the circuit boards. The company may use the excuse that you "tampered" with it and won't honor the warranty.

Samsung has authorized a number of agencies around the world to repair their products, not just their own warranty service depot. Any authorized service depot could have temporarily replaced the bulging caps in my monitor before determining that the caps were not the cause of the continuing fault.

I put back all the original Samsung capacitors on my IP board and the Samsung warranty technician will readily observe that they are bulging and therefore their product is suspect.

Different jurisdictions have consumer laws concerning the legitimate repair of products while under warranty. Car manufacturers once insisted that the oil be changed only by an authorized dealer in order to maintain the warranty. The consumer courts where I live have ruled that an owner can change the oil him/herself and the engine warranty will be enforced as long as a proof of purchase of the oil can be provided in order to prove that the oil was changed at the prescribed service interval.

I design and build computer interface boards as a hobby and I am confident that my 45 years of electronic handywork will stand up to any scrutiny.

[cadillacman]

Re: Samsung 266BW - blue power light stays off

my boss has one of these in his office and it just died. It will power on to a light grey screen for about a second or two then go black. blue light stays on. Going to tear into it tonight.

[cadillacman]

Re: Samsung 266BW - blue power light stays off

Here we go again with a not to simple issue even though i thought it was heh..

Ok so again this would power on to a grey screen for about 2 secs then shit off, blue power led still on.

Took it apart, apparently the sales manager at work had it apasrt, the t-con cable was disconneced. Reconnect, now i get a picture for those 2 seconds before it shuts off. 2 seconds to black kind of issue going on here...

SO i pulled the powerr supply/inverter board. Found one obious bad cap, rest are some no name krap. Replaced all caps on the power supply, fixerd some krap solder, recheck- SAME... ugh.. ive ohmed the inverters and theyre not open and read the same between each other... the backlights are not pink or flickering, it powers up to a nice pic and backlights just shut off.



WHere do i go from here? anyway to mod this to make backlights just frickin stay on?

[PlainBill]

Re: Samsung 266BW - blue power light stays off

Here we go again with a not to simple issue even though i thought it was heh..

Ok so again this would power on to a grey screen for about 2 secs then shit off, blue power led still on.

Took it apart, apparently the sales manager at work had it apasrt, the t-con cable was disconneced. Reconnect, now i get a picture for those 2 seconds before it shuts off. 2 seconds to black kind of issue going on here...

SO i pulled the powerr supply/inverter board. Found one obious bad cap, rest are some no name krap. Replaced all caps on the power supply, fixerd some krap solder, recheck- SAME... ugh.. ive ohmed the inverters and theyre not open and read the same between each other... the backlights are not pink or flickering, it powers up to a nice pic and backlights just shut off.



WHere do i go from here? anyway to mod this to make backlights just frickin stay on?

The best way to make the backlights stay on is to fix the problem.

Disconnect one of the backlight connectors, then turn on the monitor. Do the backlights come on? Now reconnect the first connector, disconnect the other, and turn on the monitor again. Do the backlights come on with the same brightness?

PlainBill

[cadillacman]

Re: Samsung 266BW - blue power light stays off

ok i have 4 backlight connectors... are you saying power it on with one connector at a time to see if i have a odd man out?

[PlainBill]

Re: Samsung 266BW - blue power light stays off

ok i have 4 backlight connectors... are you saying power it on with one connector at a time to see if i have a odd man out?

Yes. Although the CCFLs may not work unless both of a pair are hooked up. I could tell more by looking at a picture of the bottom of the power supply, but SOMEONE posted 7 pictures and didn't include the one I needed. (The picture of the bottom of the signal card is exceptionally useless.)

PlainBill