LNK420 failure - cracks in the body what can I do?

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When we use LNK420 with power supply 75 W we have got cracks in the body. The photos are attached. Does it happen often with LNK420? What is the solution?

This is unusual. Can you provide more info about the test conditions? Is the failure repeatable on all parts tested?

I apologize. I will be brief, i will clarify the situation.

This is not regular. At the moment is sporadic failure. It was noticed to me that this failure occurs duren transient processes:

- cyclic switch on/off power supply

- powerfull surge transients (this it indicated by a destroyed varistor, Y2 capasitor and fuse)

So, i`m inclined to think that the engineer made a lot of mistakes when developing a power supply:

- PCB. Design is bad. Does not even meet your recomendation. Reality, is not possible to obtain power above 45 watts, system is not stable. The situation is corrected by adding С18?

- BOM. No logic. 100V shottky diode (VS-12CWQ10FN), under doubt transformer configuration (ETD29 0,7mm gap N87 Pri: 81T Sec: 20T Bias: 13T), clamp network (1.5KE250), wide range of regulation current (30V 45-75W), C18 in parallel FB pin (Kirchhoff`s circuiit laws ?)

- As a result we have: low PF (about 0.9), unstable current regulation (more 5%), switch off PS if input voltage under 175 VAC (OVP triger), flickering 30-50% 

Files of project attached. This design copy of RDR-290.

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