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TonyDuell · 25th Mar 2021, 4:54 pm

Oh bother...(that's the family-friendly version).

Turns out there's a mosfet in series with the chopper transistor emitter circuit. It's failed open-circuit. The markings are MPT5N06, which Towers tells me is an n-channel enhancement-mode device, 5A. 60V.

Now I can't find it at RS or Farnell, I can't even find a near-equivalent (although my bitter experience suggests that SMPSUs don't like 'equivalents). Any sane suggestions as to what to try?

I think it's unlikely the transformer has failed. My experience is that kills the chopper instantly at switch-on, not after half a minute or so. The supply was running in that time, the outputs (with no load) were all present and correct.

The regulation feedback is another transformer, the chopper current sensing yet another. No low-value resistors. The only electrolytics are the mains and output smoothing capacitors, I intend to replace the lot.

25th Mar 2021, 4:54 pm	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,222	Re: Weir HSS100/4 PSU blowup Oh bother...(that's the family-friendly version). Turns out there's a mosfet in series with the chopper transistor emitter circuit. It's failed open-circuit. The markings are MPT5N06, which Towers tells me is an n-channel enhancement-mode device, 5A. 60V. Now I can't find it at RS or Farnell, I can't even find a near-equivalent (although my bitter experience suggests that SMPSUs don't like 'equivalents). Any sane suggestions as to what to try? I think it's unlikely the transformer has failed. My experience is that kills the chopper instantly at switch-on, not after half a minute or so. The supply was running in that time, the outputs (with no load) were all present and correct. The regulation feedback is another transformer, the chopper current sensing yet another. No low-value resistors. The only electrolytics are the mains and output smoothing capacitors, I intend to replace the lot.