Please help me find 7 pin smd ic 901 part number in Delta DPS-300AB-76 LED Display Power Supply

[Gentian]

I have a 5V 55A led Delta power supply with no output. I found this 7 pin IC 901 damaged as in the photo. All other elements look ok. I checked and every other surrounding componets diodes, resistors and capacitors look ok. I have 2 identical power supplies removed from a led wall which have the same defect with this ic burned but not a working one for reference. I founded by measurements that pin 7 goes to positive hot 450V 220uF electrolytic capacitor primary side. Pin 1, 2, 3, 4 connected together to pcb cooper trace. These four pins goes to negative side of 10uF 50V electrolytic capacitor numbered C903. They goes also to cathode of black diode numbered D902 (diode anode to HOT ground of 450V 220uF capacitor). The D902 cathode side is also connected to pin 6 through paralelled 2 kOhm 1% tolerance resistor numbered R901 and a small smd capacitor in the range of nF I suppose (not able to measure on circuit through RLC meter). Also from the cathode joint a 120nF smd capacitor numbered C902 with the other side connected to pin 5. Pin 6 goes also to positive of C903 capacitor through 16.5kOhm resistor numbered R902. The positive pin of C903 connected to cathode to another diode numbered C903. I found a 65 Ohm resistance from pins (1,2,3,4) and pin 5. Removed IC901 this resistance disappeared from the circuit of pcb. IC 901 exploded and no numbers can identified. Please help me find the IC type to replace it. Power supply has no output 5V 55A and fuse not blown and also I see a 320V DC voltage in the 450V capacitor.

[R_J]

Look inside the case to see if you can find the top of the ic, sometimes you can find it.
are you sure about pin 1? it might be a TinySwitch-III TNY-280G

[Gentian]

Dear R_J thanks very much for your help. I checked the tinyswitch datasheet and I am not sure this is the IC i am trying to identify. In the description i am refering pinouts as in the photo attached. I see pin 7 directly connected to positive of DC big capacitor. In the datasheet I see a network beetween this pin and positive HV DC. Also in the board are two photocouplers but seems not resistance from any pin of IC 901. to them. I don't know maybe another type of IC?

[R_J]

I think I found it...
It won't be a tny-xxx, it might be a Power integrations LinkSwitch-TN LNK302/304-306 The D package (SO-8C)

No switching transformer or opto's required, also the layout seems to work

[CapLeaker]

Also an LNK364pn has that pin out like the TNY.

[Gentian]

Dear R_J thanks a lot. Yes I am checking and think TN LNK302/304-306 is IC901. I see you added L1 in the schematic which I didn't take into account in the first survey. I measuret the path and since its dc resistance is very low it looked like a simple short wire. Based on your very well explained photo of the Power supply board, I used a LCR meter and it shows a value of 1.14mH. Very close to that of the buck converter example in the datasheet for L1.
So I will try to order a LNK306 D sop-8c IC and make the replacement.

I have some LNK564PN, TNY264, TNY266 PN but I think they are not a candidate for replacement or if someone has an experience to use them as buck converter please suggest me.

Also I want to ask, based on the photo of the exploded IC 901 (probably LNK 306 D), what could have been the reason of such violent damage? Since I found a 65 ohm resistance between source and BP pin and open circuit Drain-Source?

I will take a short period since receive the lnk306 and after replacement I will write again here.

Thank you very much!

[R_J]

The ic is connected to the raw dc produced from the ac line and the main filter. a spike on the power line may have caused it I really don't know. I can only see into the future not into the past.