Small capacitor near aux flyback transformer

[derkraken]

I've just recapped a 145w "power man" micro atx supply, model number
FSP145-50NW.

I replaced two vented YEC 3300uF 10V with two Hitano 2200uF 10V as those were the only parts I had that would fit.

I also replaced a 47uF 35V capacitor next to the auxiliary flyback transformer, which had vented without bulging - I could see a brown mess on top and on adjacent parts. It was completely open circuit.

The nearest part I had was a 33uF 35V which I scavenged from a lexmark printer power supply - I don't live near any shops that sell low esr capacitors.

My question is whether or not these are suitable substitutions. I am particularly concerned about the 33uF substitution. I've read here that other posters tend to substitute higher value capacitors. The power supply now runs with a HD attached, and the voltages all seem OK, but I don't have any MB to test it in.

The supply will go back to my brother's very low end machine - one HD, cd-rom, on board video, dial up modem, 192mb ram and 466 celeron processor.

Thanks. I'm sorry I don't have any pics because I don't have a digital camera,

[linuxguru]

Re: Small capacitor near aux flyback transformer

If it's a long-life series (4000+ hours), it should be OK. I tend to use a larger value (100uF/35v) in that location - either NCC LXA or Elna RJJ, because the cap tends to fail open with very little capacitance at that location.

The change of value only affects the transient response of the control loop for +5Vsb - since the load on +5Vsb stays pretty much constant after power-up, there's not much impact from substituting a different value. If it powers up and down, you should be OK.

If you put too large a value, it's possible that some integrated controllers (e.g. TopSwitch) will not start up at all.

[derkraken]

Re: Small capacitor near aux flyback transformer

Thanks very much for the reply. The cap was a Newcon wp, which according to their datasheet is rated for 2000 hours. I think it is probably still acceptable, as I can't see the machine it'll be in being used forever and a day!