Samsung 204t Blinking Green Light

[theonetrueace]

I replaced the cap that looked the worse, although I don't think it was the actual problem with this board. It's outputting 5v on the 13v output pins. Can you spot the problem component.

[selldoor]

Re: Samsung 204t Blinking Green Light

Which cap did you replace and with what?

Carefully test the voltage on the big cap, Meter on vDC 600

Picture of the back of the board.

Picture of the Main/logic board

[theonetrueace]

Re: Samsung 204t Blinking Green Light

Well prior to your reply I figured it's got to be something simple do to the fact that I'm getting any voltage at all. I went through and replaced the 300uf 25v caps with some I had. Low and behold I get 13v on the output. I'm then all happy thinking I fixed it, reassembled the monitor and go to test it a final time before putting it in storage. Boom, blink led again. I rage a little, disassemble it, and test it to find out I'm getting just under 4v on the output. The caps I replaced were a little bigger in diameter than the ones I replaced them with. I didn't think it would matter since I got these caps as part of a "kit" I bought off eBay previously to fix this very issue. So I ordered some Panasonic caps that are the same size as the originals. When I get them in and replace the ones I replaced I'll let ya know how it goes.

Just for my knowledge, what's the difference between two caps of different sized with the same ratings?

[selldoor]

Re: Samsung 204t Blinking Green Light

Whilst ebay caps can be risky, if they were the correct voltage and uf they usually work at least for a period. I have to ask - did you have them the right way round?

When you say ratings do you just mean Voltage and uf? often as the can size changes the esr and the ripple values change.

Different sizes for different positions eg short fat for under heatsinks or on boards that fit in narrow tvs. Long thin ones where you have the height but you need to place caps close together -eg in a pc psu

You also may have different temperature ratings on different shapes.

[theonetrueace]

Re: Samsung 204t Blinking Green Light

All the info listed was the same; 330uf 25v 105c. The cans were about the same height but the originals were visibly fatter (larger diameter). As far as having them in backwards, I'm 99% sure I installed them correctly. As I stated I got the correct voltage and the LED was back to correctly functioning prior to reassembly. That's why I figured it had to be the caps I installed. The combination of different sizes and working then not working indicated to me that they have failed. I could be wrong though. Its been known to happen.

[selldoor]

Re: Samsung 204t Blinking Green Light

As I stated I got the correct voltage and the LED was back to correctly functioning

I may have misunderstood -are you saying you had 13v and your only "test" before putting it back together was to see that the power light stayed on? did the backlights come on? or even flash? This is going to need more troubleshooting if not.


All the info listed was the same; 330uf 25v 105c.
That is not usually considered enough info to replace caps - you need to get the datasheets for the original caps and match with new. Getting similar or better ESR and Ripple.

New caps (at least good ones) have tended to reduce in size due to better manufacturing techniques.

[theonetrueace]

Re: Samsung 204t Blinking Green Light

I may have misunderstood -are you saying you had 13v and your only "test" before putting it back together was to see that the power light stayed on? did the backlights come on? or even flash? This is going to need more troubleshooting if not.

You are correct, prior to reassembling I tested the voltage on the output to the logic board and looked at the LED on the power button. Previously it was blinking, then at the point where I had 13v out it was on solid. I didn't check to see if the backlight was working, no. I was more interested in getting it hooked up and I couldn't do that without reassembling it and moving it closer to my workstation, due to my cable management situation. I'll mess with it more and update the thread when they other caps come in.

That is not usually considered enough info to replace caps - you need to get the datasheets for the original caps and match with new. Getting similar or better ESR and Ripple.

New caps (at least good ones) have tended to reduce in size due to better manufacturing techniques.

Oh, woops. I'm a software developer diving into the world of hardware so I'm out of my element. We'll see what happens. Worst case scenario I'm out an additional $25 for a replacement power board.

[theonetrueace]

Re: Samsung 204t Blinking Green Light

So I finally got back around to looking at this power supply today. I tested some points trying to track down the problem and found something curious. It's a ceramic cap which has different voltage readings on the two sides. Tell me what you think of this... image attached...

[budm]

Re: Samsung 204t Blinking Green Light

The one on the right of the X/Y safety cap is the primary side (hot) so you do not use Safety ground or chassis ground as the ground ref point for taking the Voltage, yo use the negative leg of the main filter cap as the circuit ground ref point.
The secondary side (the left side of the safety X/Y Blue cap) you can use the chassis as the ground ref point because the secondary circuit ground is tied to the chassis.

[theonetrueace]

Re: Samsung 204t Blinking Green Light

Forgive my ignorance. Can you please circle the "negative leg" of the "main filter cap" on one of the photos. Thanks in advance.

[budm]

Re: Samsung 204t Blinking Green Light

I cannot see the band on the side of the cap, but all your have to do is to measure the DC Voltage right at the two legs of the cap, it should have 165~170VdC, but at this point you power supply is working otherwise you will not have any LED indicator on the monitor.

[theonetrueace]

Re: Samsung 204t Blinking Green Light

Well I'm at the end of my hardware diagnostic ability. Any suggestions on what to check? I've replaced the caps again to no change in functionality.