Cooktop SMPS repair


New member

I'm trying to repait a SMPS in an induction cooktop hope it's not a problem that only the repairment is DIY... :)
I attached the schematic, the problem is: it's providing the desired 24V for a few minutes but after 5-10 minutes it goes down.
0V at output, 310VDC is till on and the TOP254 is trying to boot (C pin jumping between 4.8V and 5.8V) but can't get up I don't know why.
What should I check? What can be the cause? Is it a thermal warming up that turns it down?
And after it warmed up even if I turn it off and on again it wont start so something is built up that's causing the problem.
After letting it cool down for on hour than it goes again for a few minutes...

- originally it produced just 16V instead of 24V
- I measured all passive parts (diodes, resistors) with DMM and they look OK
- then I replaced all the electrolytic caps (and so far now for low ESR/L types unfortunately)
- then I replaced the Opto, the TL431 and the TOP254
- then the 24V came back but it's not stable...
- even the load is not cut off from the SMPS

Please help!

Thanks in advance!



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New member
Ehh, strange yesterday evening I get back to this project but now everything was stable...
There was't any turning down or instability. I even tried it with dummy load up to 500mA and it was solid as a rock.
I put iut back to the cooktop and so for everything is ok. I'm not sure wat was the last problem maybe it was just too late in the evening.
Anyways the last part I replaced between the surely bad state and from now was the original opto I put back.
It'd be great to know what exactly was the difference but I can't guess other the the CTR of the opto.
Now a real life test will be performed for days and I'll come back if anything is coming up.