VOGONS


First post, by kotel

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Hi

Finally decided to get this HP ATX0300F1 REV. A PSU recapped. Theres only 1 4700uF 10v cap that is bulging and I can see some leakage on it too. PSU works okay. It looks like it smooths out 3.3v rail since its connecting it to ground. I only have 6800uF 25v cap and 3300uF 25v cap closest to the specs of the bad one. Is it possible to use the 3300uF cap since with the 6800uF one I will have troubles fitting it in place?

"Driving a tank is like a box of chocolates. You never know when you blow up"
- Someone from a tank game

Reply 2 of 4, by Deunan

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kotel wrote on 2024-05-19, 17:56:

Is it possible to use the 3300uF cap since with the 6800uF one I will have troubles fitting it in place?

You should really look for a suitable replacement. You don't want smaller capacitance, this will result in higher ripple and might affect the system. Yes, electrolytic caps can have rather high tolerance of -20% to +50% but most modern ones are pretty much spot-on. A higher value can upset the PSU, esp. during startup with heavy load, but 6800 is no so far off 4700 that it wouldn't work I think. Still, better to find a proper match.

Also you do not want much higher voltage, this will increase the ESR and you do not want higher ESR in the rail filter of a switching mode PSU. Not only will this increase the ripple, but also the power loss and thus temperature of the cap. It will fail sooner. So for 3V3 rail you want 10V caps, perhaps even 6V3 ones. Low ESR, preferably 105C rated (or higher if it doesn't affect ESR).

Reply 3 of 4, by kotel

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Found the lost 4700uF 16v cap. Although its legs are too short so now I will either solder on some leg-sized wire or order some proper caps.

"Driving a tank is like a box of chocolates. You never know when you blow up"
- Someone from a tank game

Reply 4 of 4, by majestyk

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kotel wrote on 2024-05-19, 17:56:

...Theres only 1 4700uF 10v cap that is bulging and I can see some leakage on it too.

This doesn´t mean the others are still within specs.
It´s probably just a matter of time, until other electrolytics in the secondary section fail. Better look if there are more caps of the same type / same manufacturer and replace them while you are still at it.