About Dell ST2220L power card problem

[SamH]

Dear BG members, I have been using this monitor since 2011. A couple of months ago, suddenly, the monitor is exhibiting power supply problem & dead after few days. Unlike today's monitor, this have the card housed inside the main panel, and, I dismantled this & checked to confirm, the problem is indeed in the power module, not in the LCD Panel. So, the repair of this monitor is possible if replace this (power card/module) with a good one. Below snaps are posted for references.



Dell ST2220L 21.5-inch FHD




Power Card: 4h.17B02.A00

Therefore, I'm requesting your support to know, where can I get a new/compatible power card for the above? Or, anybody knows, who repairs faulty SMPS power module of monitors/pcs.

Thanks in advance.

[Swapnil]

I actually have a dead SMPS board of HP LE1851W sitting right here on my desk. You can find replacement boards online, but the cost including shipping would be more than the price of monitor itself. And repairing a SMPS without proper testing tools and expertise would be next to impossible. I don't know any shop has either of those.

On the other hand, I suspect in my case, the board's CCFL inverter is still working. I have separated the inverter part and SMPS part of the circuit, and actually planning to plug in a computer power supply's 5v and 12v line to the appropriate points of the circuit. If you want, I can post here how my experiment goes.

Warning: Don't go probing with a multimeter when plugged in. Actually, don't even plug the board in when open. That big capacitor holds 322 volts even after unplugging the power cord.

[redwan hasan]

I actually have a dead SMPS board of HP LE1851W sitting right here on my desk. You can find replacement boards online, but the cost including shipping would be more than the price of monitor itself. And repairing a SMPS without proper testing tools and expertise would be next to impossible. I don't know any shop has either of those.

On the other hand, I suspect in my case, the board's CCFL inverter is still working. I have separated the inverter part and SMPS part of the circuit, and actually planning to plug in a computer power supply's 5v and 12v line to the appropriate points of the circuit. If you want, I can post here how my experiment goes.

Warning: Don't go probing with a multimeter when plugged in. Actually, don't even plug the board in when open. That big capacitor holds 322 volts even after unplugging the power cord.

Have you seen the 3rd leg of IC601? Seems normal to you?

And by the way most SPMS actually has issues with capacitor, often times replacing them solves the issue.

[SamH]

Thanks Swapnil and redwan hasan for your response.

@Swapnil
This is a LED back-lit panel, so don't have CCFL inverter, but have a LED driver unit in a separate PCB. I have checked both the HV & LV side, and found voltages till the big capacitor (c605). That is, its okay till the full wave bridge rectifier. It's possible, the switching circuit for the ferrite core transformer is gone, or the transformer itself is gone. But, there is no way to test in-house all of these. Here I labeled the snap for better understanding.

That big capacitor holds 322 volts even after unplugging the power cord.

Yes, thanks, I know that. So for handling I discharge this with a flat screwdriver always.


@redwan hasan

IC601 is TOP258PN (35Watt power supply IC), and its pin layout is okay; I mean, manufactured in that way. Datasheet link is below.
http://www.farnell.com/datasheets/5827.pdf

[Swapnil]

Have you seen the 3rd leg of IC601? Seems normal to you?

And by the way most SPMS actually has issues with capacitor, often times replacing them solves the issue.

Looks like TOP258 doesn't have a pin there. And also it looks like there is a odd 90 degree bent jumper wire down there, which seems to be corroded somehow. Similar thing under the ceramic caps. Could be the reason for the problem, could be not.

Thanks Swapnil and redwan hasan for your response.

@Swapnil
This is a LED back-lit panel, so don't have CCFL inverter, but have a LED driver unit in a separate PCB. I have checked both the HV & LV side, and found voltages till the big capacitor (c605). That is, its okay till the full wave bridge rectifier. It's possible, the switching circuit for the ferrite core transformer is gone, or the transformer itself is gone. But, there is no way to test in-house all of these. Here I labeled the snap for better understanding.

Yes, thanks, I know that. So for handling I discharge this with a flat screwdriver always.

You can try replacing all the electrolytic capacitors on the board. You can find another thread I've opened about a Samsung monitor. I got that one fixed by replacing all the caps. If the big bulk cap is holding charge, then no need to replace that as it might be very costly, but replace the smaller 1000uf ones and see if it helps. Also, if those jumper wires look corroded, try replacing them too. And finally, if all fails, try to find the service manual on the web. You can find circuit diagrams or at least block diagrams there, find out the pinouts of the LED driver board and mainboard connection, and see if you can replace this whole board with a ATX computer power supply. The main issue would probably be power on signal, or if the dimmer signal is passed through the SMPS board to the LED driver board. If that works, the setup will look like crap, but who cares about that if it works?

[redwan hasan]

Capacitors look okay to me, can't see the 68uF capacitor's top however but the thing is I'm not seeing much on this board that can be damaged or sign of damage except for the corrosion and as the datasheet suggest the 3rd pin is not even been used so I think its well and good there.

You might wanna download the PCB diagram and check voltages on different points and compare it to the original design to see if you can figure out the damaged section, that's how I fixed my TV couple months ago, fortunately TV circuit diagrams are easier to find.

[SamH]

Thanks both of you for your good intent to help me. Today, I visited Stadium market, got IC TOP258PN for BDT80.00, replaced in the board and problem solved.

But, by this time, I already bought another Full HD dell monitor (22") from computer source. So, I have a penalty of BDT 12,000.00 for the incident.

[Swapnil]

Capacitors look okay to me, can't see the 68uF capacitor's top however but the thing is I'm not seeing much on this board that can be damaged or sign of damage except for the corrosion and as the datasheet suggest the 3rd pin is not even been used so I think its well and good there.

You might wanna download the PCB diagram and check voltages on different points and compare it to the original design to see if you can figure out the damaged section, that's how I fixed my TV couple months ago, fortunately TV circuit diagrams are easier to find.

Sometimes electrolytic caps can still be dead when looking physically OK. That's what happened with my Samsung. And about probing for voltages in different point, that's how I blew up half of my HP's SMPS board. I was little bit careless though.

[redwan hasan]

Thanks both of you for your good intent to help me. Today, I visited Stadium market, got IC TOP258PN for BDT80.00, replaced in the board and problem solved.

But, by this time, I already bought another Full HD dell monitor (22") from computer source. So, I have a penalty of BDT 12,000.00 for the incident.

now sell me the FHD monitor for 5k
anyway good to hear that.

- - - Updated - - -

Sometimes electrolytic caps can still be dead when looking physically OK. That's what happened with my Samsung. And about probing for voltages in different point, that's how I blew up half of my HP's SMPS board. I was little bit careless though.

yeah I know or maybe the capacitance goes to point where it is not enough for the power supply. Good that you didn't blow up the entire grid.

[SamH]

I only gone to repair the board after posting here in BG. Before that, I searched many places where I could get a replacement board, but failed. As SMPS usually non-repairable due to use of many Surface Mounted components. But, I'm lucky, only the switching IC was damaged in this case.

BTW, both are FHD monitors. Older is TN panel, the newer is IPS panel. And I'm going to keep both.