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Old 05-06-2021, 01:28 AM   #7
momaka
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Join Date: May 2008
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Default Re: DTK 400W PSU Power Good signal 0V fault

Quote:
Originally Posted by PanicMechanic View Post
Yeah, I was the one who changed the output caps on it, years ago. I had put a very low ESR Japanese capacitors in it, an after that it developed a fault. The output was oscillating at about 800 Hz and 1.2 Vpp on the 12 V line (under 100 W resistive load). Not the ripple, the ripple was low, about 20 mVpp or something. It seemed that the TL494 does not like very low ESR output caps. So I replaced those with worse caps (higher, but still "low ESR") ones, and the situation was improved. It was still oscillating, but at much lower peak voltages (but still about 200 mVpp if I remember correctly), so it is not ideal.
Yeah, that's quite possible. Many of these older half-bridge PSUs don't like ultra-low or very low ESR caps. That said, I did use United Chemicon KZE 16V, 3300 uF cap on mine above for the 12V rail, and it seems to be pretty solid in terms of operation (at least I never had a PC crash because of it.) Otherwise, mine too oscillates a little when under light load, though I didn't measure it (don't have a scope). I can just hear it "whining" slightly when not loaded much. Once loaded up, though the noise disappears.

In any case, I still suggest you at least check the small caps first, especially the GL -branded ones. At this age, they really probably have failed. On mine, they were Fuhjyyu... which as bad as people say this brand is, isn't nearly as bad as GL and CS, IMO, as mine are still in spec. The newer Macron that I got came with PCE-TUR caps, and those also turned out to be OK. But the CS-branded caps on the output were starting to fail high leakage/capacitance.
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