Hi,
I am looking for help to fix a dead ATX SMPS.
Background; I bought a new NorthQ 4001AT 400Watt SMPS. The unit was DOA, and the seller replaced it immidiately and didn't want the defect one in return. So I want to fix it - as all components in it are new it may just be a minor fault and it may serve me for a long time, besides I would be very satisfied if I could manage to fix it. The SMPS is dead - when PS_ON (green wire) is connected to earth I hear a small 'tick' from the SMPS and the fan blades moves half an inch. There is no voltages on any of the outputs. When doing these tests I load the +3,3 +5 and +12 Volt outputs with minimum loads (as read on the box) in the form of power resistors. When testing there is over 300 V across the two HV capacitors, and half the voltage between the two. There is 3 power transistors in the primary circuit 2 pcs J13009 and 1 pcs C5027-R. When testing these with an DMM all junctions seems fine. There is +5V between pin 5 and 9 on the ATX power connector.
I would like to ask for help to continue troubleshooting from here. At least parts of the primary seems to be OK. I have read somewhere that a possible fault can be the startup resistors of the primary transistors, and that these resistors usually have quite a high value. But I cannot find any resistors with large values around these transistors. I have some experience with electronics, but little with SMPSs. I have experience with tube amplifiers so I am used to watch myself from B+.
The semiconductor components I have located in the SMPS are;
Primary;
2 x J13009 NPN Power BJT 1 x C5027-R Hi-Volt BJT diodesSecondary;
2 x SB3040PT Schottky Barrier Rectifier 4 x component TO-220 3-pin 1 x LM 339N Quad comparator 1 x KA7500B 5V reference 1 x 4-pin DIP component 8 x small 3-pin BJT or similar lot of diodesThank you for helping me. marty