Linkworld 200W AT PSU with Fuhjyyu caps

[Rainbow]

I've got a 1994 Linkworld 200W AT PSU. All caps are Fuhjyyu except the two big ones which are CapXon. They're all OK, the fan is OK too. I've only cleaned the dust from inside and it runs fine like new

[Newbie2]

Re: Linkworld 200W AT PSU with Fuhjyyu caps

I'm sure in 1994 the cap problem didn't exist until 5 or 6 years later.

[linuxguru]

Re: Linkworld 200W AT PSU with Fuhjyyu caps

If the CapXon are 220uF/200v, then it's likely that the specs are over-rated on the SMPS - it's probably a 135W/165W claiming to be a 200W. Almost every commodity 200W AT SMPS in that era used basically the same topology - a half-bridge push-pull forward converter with self-starting primary, a TL494 (with an LM339 or a few transistors for the protection circuits) on the secondary side for regulation, driving the primary side through a small transformer that is also part of the self-oscillation circuit of the primary.

Devilishly ingenious, and also the lowest-cost circuit topology for that power level (135W to 200W). The only problem is that many manufacturers skimped out and used smaller parts, but left the specs unchanged at 200W. Some of these will be missing the input filter circuitry, the high-voltage varistors across the primary capacitors, various output inductors, etc. They'll also have ridiculously small capacitors (1000uF) on the secondary, with some capacitors omitted.

Try loading up your system with a few drives, and watch the +5v drop to +4.3v and the +12v drop to +11v. I usually replace the 1000/10v on the +5v with a 2200/10v, and the 470/16 on the +12v with a 1000/16v. This doesn't improve the rating of the SMPS - if it's overloaded, it remains overloaded - but it does improve the transient response and helps reduce the random reboots and shutdowns that sometimes occurred when a drive motor started spinning up and so on.

It also helps to put 250v MOVs across each of the primary capacitors if there are unpopulated locations for the MOVs (usually marked ZNR1 & ZNR2). It improves reliability in places with noisy/spiky mains.

[PeteS in CA]

Re: Linkworld 200W AT PSU with Fuhjyyu caps

That puppy could easily have 40,000 or 50,000 hours on it. Those O/P caps could be at wear-out, and I'd watch that fan like a hawk. If the I/P caps are 220uF, 200V changing those to 330uF or 470uF (probably in the same or smaller case size) would help with the wimp factor, though the switch device and O/P rectifier heatsinks are another thing frequently skimped on and not easily improved.