Too high input capacity or…?

[Behemot]

Yo guys. U have this shitty old Eurocase "500 W" PSU. Few years back I recapped it, than half a year back I swapped the input caps (820 uF) for bigger, 1000 uF.

Since than I was sometimes hearing strange sounds, now lately it is even worse, PSU is powering off when running with no load. With load it is not better, one MoBo is not even powering up, well, I do not blame it, output on +12 V is just 10,5 V.

Do you think too big input capacity may have affected compensation? Or something just weared off independently on this thus making compensation unable to drive the voltage?

P.S.:
Anyway, call this my lucky day, I connected different PSU which I slightly reworked and already blewed once (there was short on primary or something). This is better made than the Eurocase, even it is LC Power. Well, this time secondary blowed, than primary again. I won't repair it for second, the PSU does not like me Will use it for parts, just pity for all the time I have already gave into it…

[tom66]

Re: Too high input capacity or…?

If anything, the higher capacitance will have helped. Can't think it would cause problems.

[PeteS in CA]

Re: Too high input capacity or…?

The main consequence of higher input capacitance is longer hold-up time during poer line sags or drop-outs, which is usually a good thing.

[Behemot]

Re: Too high input capacity or…?

That means either I had to chage something else during the process (even just by moving with something and for example making transient resistance), or something just weared off independently on this.

Or I changed some small cap(s) and forgot

[tom66]

Re: Too high input capacity or…?

The only disadvantage could be higher inrush... but that would probably only apply if you were using 2-3x more capacitance, you've barely gone up 20%.

[ben7]

Re: Too high input capacity or…?

I don't think bigger caps would make the voltage sag, I bet the secondary caps you used were not the best. What brand are the secondary caps?
Its also common for the transformer to whine if there are bad output filter caps.

-Ben

[Behemot]

Re: Too high input capacity or…?

Samxon RS, RL, maybe some GK (the small ones), everything from Joe.

[momaka]

Re: Too high input capacity or…?

If that Eurocase is a cheapo PSU and more than 3 years old, chances are the 2-transistor self-oscillating standby circuit in it is probably close to committing suicide.

Make sure the output caps on the 5VSB rail are good and also change the "critical" 5VSB capacitor (usually 10uF, 22uF, or 47uF on the primary side near the 5VSB transformer), if it has one.

Otherwise, prepare for over-voltage on the 5VSB + dead motherboard + maybe explosion (or at least a few burned components overtime). I had a crappy Raidmax PSU burn a the PWM controller's Vcc resistor due to a bad cap in the 5VSB output because the 5VSB would not regulate properly (for that PSU, 50mA of load on the 5VSB was actually enough to put the 5VSB circuit out of regulation and all over the place).

[Behemot]

Re: Too high input capacity or…?

I remember the +5 V SB cap was poped by the time I changed it for Samxon, thats true. It is much more than 3 years old, but actually has been in daily use for probably less than two years, than just for testing.

[momaka]

Re: Too high input capacity or…?

I remember the +5 V SB cap was poped by the time I changed it for Samxon, thats true.

Not sure what you mean by the "5VSB cap". There's usually more than one associated with this circuit.
I guess you were talking about one of the output capacitors. But what about the small "critical" cap on the primary side - does your PSU have one and did you change it? If it does and you haven't changed it, that would be a good explanation for the strange noises.
If your PSU doesn't have the critical cap, then perhaps it just has a noisy 5VSB circuit. I have a few quality OEM PSUs from Astec, Lite-On, and Delta that do this.

[Behemot]

Re: Too high input capacity or…?

I am sorry, this PSU is currently on the bottom of my priority list. But I will post pics and stuff when it will move higher, don't worry This platform used to be pretty common arround, I guess it won't harm when you will get to know it guys

[Behemot]

Re: Too high input capacity or…?

Hey I forgot to update this thread back than. I've resoldered some joints, I remember one was somehow loose, it is working since than. I always take it out from under a table now and than for testing, than put it back. had to resolder wiring couple tines, those el-cheapo cables tend to crack by the connectors all the time. Maybe one day I will even put better cables in it lol.

Now it runs an Athlon 64 X2 6000+ on some Foxconn board (which should not support 125W CPUs ) for couple weeks crunching BOINC.