Norcent LT-3250 need help to identify a resistor

[woaimi]

With the momentum of getting an LCD fixed for a friend, I decided to try another LCD. This one I picked up for myself from an e-waste place for $30. I plugged in the wall and I heard a small crack and that was it, standby led was off.
I was sort of expect to see something cracked open or burnt but couldn't find one so I disconnected everything and plugged it in again hoping that I could get some voltage at the outputs.
I found no noise and also no voltages at the outputs. The main filter cap measured 163v and got 16v to the small transformer and end there. I didn't realized until the guy at work told me that sometimes it requires a load to be functioning.
I plugged everything back and powered it up. The standby led was on steady, I heard that hissing noise as it was trying to come on and then a loud cracking noise, standby led immediately gone on blinking mode.
I inspect the board again and found the resistor that goes behind the filter cap is cracked open.
The PS is made by Delta Electronic and the model is DPS-180TP, this PS is also being used in an ACER tv but only sold in Europe. Now the questions:
1. Could someone help me to identify that resistor; resistance and wattage?
2. What might be causing that resistor to crack like that?

I appreciate every comments or suggestions. I'm here to learn and will try my best.

[tom66]

Re: Norcent LT-3250 need help to identify a resistor

That is a fusible resistor, it's exact value is not critical, it needs to be 10 to 33 ohms at 1/2W to 1W, but -must- be fusible type.

The only way that could burn is the chip being powered off it is shorted - ICE380...xxx

[woaimi]

Re: Norcent LT-3250 need help to identify a resistor

thanks Tom66, I'll see if I can find those on the spare parts. But if it was the ICE3B0565 chip was shorted then it should have been blown open even when I had the PS on without any loads, right? in fact I played with the PS without loads quite a lot (tried to find out why I had no voltage at the output) and I was getting around or higher 14v at the Vcc pin, datasheet suggested from 8.5v -21v. It's only blown as other boards connected.
thanks again

[tom66]

Re: Norcent LT-3250 need help to identify a resistor

Hmm, it may be OK then. Try replacing it, then connecting a 10 ohm, 10W resistor to the output, if you can easily get one. If the PSU copes with that, then it should be OK with the main board. That's assuming it has short circuit protection, which it might not, so there might be a short on the main board.

[mariushm]

Re: Norcent LT-3250 need help to identify a resistor

I'm not sure but it looks more like a 39 ohm resistor to me.

[budm]

Re: Norcent LT-3250 need help to identify a resistor

It looks like 0.3 Ohm 5% MOX Fusible resistor, cannot tell what that resistor is feeding. cannot see the whole bottom side of the board.

[woaimi]

Re: Norcent LT-3250 need help to identify a resistor

"Hmm, it may be OK then. Try replacing it, then connecting a 10 ohm, 10W resistor to the output, if you can easily get one. If the PSU copes with that, then it should be OK with the main board. That's assuming it has short circuit protection, which it might not, so there might be a short on the main board."

I have some 7.5 ohm at 5W do you think that'll work

"It looks like 0.3 Ohm 5% MOX Fusible resistor, cannot tell what that resistor is feeding. cannot see the whole bottom side of the board."

I'll get a full underside photo of the board when I get home tonight.

thanks guys

[tom66]

Re: Norcent LT-3250 need help to identify a resistor

If you have three 7.5 ohm, tie two in series and parallel one with it - this makes an 11.2 ohm resistor. If you only have two, tie two 7.5 ohm in series to make 15 ohms. Both will represent typical standby loads. As the resistors are only 5W, do not do this for too long (max 30 seconds every minute should be fine) to limit the risk of overheating the resistors.

[woaimi]

Re: Norcent LT-3250 need help to identify a resistor

I took a couple photos of the back, hope they are clear enough for use. I'm gonna see if I can find any 10W resistor from my spare parts.

[tom66]

Re: Norcent LT-3250 need help to identify a resistor

The 7.5 ohm 5W will work.

[budm]

Re: Norcent LT-3250 need help to identify a resistor

7.5 Ohms will be way too high since it is used for the 12V/24V MOSFETs Half bridge drive circuits. You need to check the two MOSFETs I redlined for shorts.

[woaimi]

Re: Norcent LT-3250 need help to identify a resistor

wow! my hat's off to you guys.
The mosfets are K3569 and the readings from measuring off circuit are (meter set at 200):
mosfet #1: 1-2 = 2.0 ohm / 1-3 = 1.7 ohm / 2-3 = 0.5 ohm
mosfet #2: 1-2 = 0.6 ohm / 1-3 = 0.5 ohm / 2-3 = 0.3 ohm
i think these are gone; I spoke with sale reps at digikey and was told these are discontinued and they offered an equivalence mosfet instead. I found a few sellers offer them on ebay but they are all from china.

[budm]

Re: Norcent LT-3250 need help to identify a resistor

That makes sense, that fusible resistor is there to protect the circuit from blwoing up in smoke, you can replace that resistor with slo-bloe fuse but you will need to measure the current draw. You should also replace that SMP IC which drives the MOSFETs, it will usually get damaged when the MOSFET shorted not, now worth blwong you new MOSFET due to damaged IC. Also need to check the reistor/diode network that are connected to the GATE of the MOSFET.

[Jerry7591]

Re: Norcent LT-3250 need help to identify a resistor

all smd's with 0 in pic are in a sense fuses in case you didn't know. Just trying to help. Should read 000.ooo LOL

[Jerry7591]

Re: Norcent LT-3250 need help to identify a resistor

http://www.hobby-hour.com/electronics/smdcalc.php

[woaimi]

Re: Norcent LT-3250 need help to identify a resistor

"You should also replace that SMP IC which drives the MOSFETs, it will usually get damaged when the MOSFET shorted not, now worth blwong you new MOSFET due to damaged IC"

I'm not sure if I understand you correctly, is SMP IC is the ICE3B0565 ic that got mentioned earlier?

Jerry7591, I have trouble following your suggestion, can you explain more?

[budm]

Re: Norcent LT-3250 need help to identify a resistor

The one on the left with 16 pins as shown in my post11

[woaimi]

Re: Norcent LT-3250 need help to identify a resistor

Well, with other stuffs that I have going in life this tv set has been collecting dust in a corner. I recently found a ps on fleebay, bought it, put it in place. Now I have the indicator LED come on red then green as I push the ON/OFF button. However, nothing appeared to be on. I tested all outputs from the ps and they provide the exact voltages as indicates on the board, except the PS_ON was at 4.5V (a little low I think) and remain unchanged as I turn the set ON and OFF.
Where do I go from here? The screen is completely dark, I can hear a really soft humming noise from the speakers.

thanks

[woaimi]

Re: Norcent LT-3250 need help to identify a resistor

may be I should start a new thread since it's completely different issue from this thread headline.