HSPY-400-01 Bench PSU blows fuse every time switched ON.

[ocset]

Hello,
Does anyone have a schematic for this HSPY-400-01 power supply?
https://www.aliexpress.com/item/32596957736.html?spm=2114.search0302.3.81.ccbb53d65TzmOP&ws_ab_test=searchweb0_0,searchweb201602_0,searchweb201603_0,ppcSwitch_0&algo_pvid=c7aae6c6-d073-4ea2-9d64-8d3c64182897&algo_expid=c7aae6c6-d073-4ea2-9d64-8d3c64182897-10

…ours blows the fuse with a loud bang every time its switched ON. It worked fine till three weeks ago.
Whilst I am disassembling it, and taking photos so I can re-assemble afterwards, does anyone know if there  is a common failure mode with this PSU?

I am wondering  if it has a inrush relay which has failed with locked contacts. Its going to take me a while to  disassemble as it has common mode chokes swinging in the gap between upper and  lower main boards, and I am photo’ing it all so I know how to re-assemble it. So I am just  planning ahead.

This shows another post abotut this PSU
https://www.eevblog.com/forum/testgear/hspy-power-supply/

[CDaniel]

That should be a SMPS , many components can fail , from input bridge rectifier to power transistors ... if it blows the fuse , the shorted component shoudn't be very hard to indentify .

[rvalente]

Start measuring the obvious components, just like our friend suggeted.

After that, you can add a 60-100W lamp in series, the lamp will glow but, you can now poke around with your multimeter and check for shorts.

[nctnico]

For this price I'd buy a new one. And... a power supply specialist shouldn't have a problem diagnosing a switching PSU.

[Kleinstein]

At low weight and 400 W is must be a switched mode supply. So chances are there is something broken - if not obvious visible or with experience in such repairs one would probably just buy a new one and not spend much time / money on a repair.

One could do a few in circuit tests on the diodes and power transistors. But even if finding a bad one (e.g. shorted) does not help much as chances are there are more faults.

[nctnico]

In my experience it is usually the rectifier and/or switcher mosfet if the fuse blows in the primary side. There usually isn't much else which can go wrong. I suspect that mains transient events are the main cause to deteriorate these components so other fault sources are not likely.

[ocset]

Thanks, I took a deeper look today, and indeed, it was the two switching FETs that had  gone totally short from gate to drain to source. I took them out and  was told to order new ones and then I was moved  off this job. This is a shame as I was going to analyse  this SMPS more.....

This PSU contains a top board which has a linear regulator output  stage on it. A bottom board which has the offline isolated SMPS on it. Also a front board (which I haven’t unscrewed yet) and presumably this contains the microporcessors etc. There is also a little Fan PSU board. This PSU must have given its assemblers a few nervous breakdowns.  I had to take 30 dis-assembly photographs.

The offline SMPS  bit is unusual for a 400V, 1A PSU..... It has no PFC stage. Instead there is the AC filter, and then the rectifier bridge…then a 330uF, 400v  electrolytic capacitor. Then there is the transformer isolated SMPS. This appears to be a half bridge  LLC converter (but possibly a series resonant converter of course) . It does comprise a current transformer. It does appear to have rail splitting film capacitors (each 200nF) which are supposed to protect LLC converters from startup transient damage etc. The Resonant capacitor  appears to be  1 inch long 6.8nF film capacitor.
The  68uF  electrolytic output capacitor of the LLC converter is only 400V rated…and 400V is  a bit tight for a 400v output PSU…the unit has a linear regulator output stage, so presumably the LLC SMPS is outputting a little more than 400V when the unit is outputting 400V.

The LLC  converter  ( I  believe it is that, after my short allotted time with it) looks very sparse on componentry. I cannot see a controller chip for it…….other than a IR21531S chip on a little daughter board which is a “self oscillating half bridge driver”...

IR21531S datasheet
https://www.infineon.com/dgdl/Infineon-IR21531-DataSheet-v01_00-EN.pdf?fileId=5546d462533600a4015355c8d26316b3

This is a cause for some concern, since LLC converters have failure modes which really need either a custom microcontroller solution, or a custom LLC converter IC.
Please  may I ask if anyone has a schematic for this PSU?.  I believe its very common as its so cheap, and there is another post about it here on EEVBLOG (but doesn’t go into details about the SMPS bit or any failure modes) I am beginning to suspect that its not very robust at all.

[nctnico]

Ofcourse it doesn't have a PFC stage. It is cheap from China where they don't require PFC (yet). 

[CDaniel]

When the power transistors short you should replace the controller ( IR21531S in your case ) even if it seems good ... and of course checking the rest of semiconductors for posible fails .
Maybe they used some cheap counterfeit parts  , as we know chinese use . 400V x 1A = 400W , this is serios power .

[ocset]

Thanks, and also what do you think about using a 400V cap on a 400V rail?
Also, i couldnt see any feedback  for the LLC stage...no opto or anything comming back across the isolation  barrier

[thinkfat]

Also, i couldnt see any feedback  for the LLC stage...no opto or anything comming back across the isolation  barrier

Primary-side feedback winding on the transformer?

[CDaniel]

This kind of controllers don't use feedback , the outputs are at 50% duty cycle and can't be changed . You can consider them as a transformer + rectifier+ filter cap . No regulation .

In theory for resonant converters it is possible to use feedback to modify the running frequency and achieve regulation , but this is too "fancy" for what we have here .

[ocset]

I replaced the shorted LLC converter FETs in the 400V PSU...and the IR21531S, but when i re-assembled and switched on it went bang again and wouldnt work.
Once again, the FETs blew up and were again short G_D_S
The fan works, and the LCD display, but they come off the pilot power supply  which is near  the fan.
Coming to think of it, its probably a fault with something on the output PCB.....something on there is probably short circuit........also, High voltage FETs blowing up is probably not going to do the little control & Drive PCB too much good either.

So if i was  precscribed to do further work on this PSU, then i would look to again replace the FETs and control chip. and then try and run the main LLC SMPS on its own (without being connected  to the output PCB)............if OK, i would see if their were shorts on the Output PCB.

Any further FMEA on this much appreciated as i have not been allowed more time to tinker.

[CDaniel]

Every semiconductor should be checked for obvious shorts . Especialy those diodes and SMD transistors in the grids of power transistors that are visible in pictures . An 100W light bulb in place of the fuse could save the power transistors until all issues are solved .

[ocset]

thanks, ill see if i can get more time.
I doubt it, theyll probably just buy a new one for £100.....or less if we buy direct from China.
There does not appear to be a  manual, so i dont know if it has short circuit output protection.
I suspect someone has shorted it and the output board is blown.

[marcopolo]

Maybe your 6n8 was soldered at the wrong place?