Electronics > Repair

Dell GX280 motherboard capacitor replacement (Rubycon MCZ alternative)

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WhichEndToHoldTheIron?:

--- Quote from: Simmed on January 16, 2025, 11:57:47 am ---if it is the VRM ?
i would think it needs low ESR for the Cout ?
maybe other PSU experts like to chime in

--- End quote ---
That's the gist I get, both from replies here and things I've seen on other forums. The capacitance isn't critical but the high switching speed requires extremely low ESR. Why exactly that is I don't know.

wraper:

--- Quote from: WhichEndToHoldTheIron? on January 16, 2025, 03:57:32 pm ---
--- Quote from: Simmed on January 16, 2025, 11:57:47 am ---if it is the VRM ?
i would think it needs low ESR for the Cout ?
maybe other PSU experts like to chime in

--- End quote ---
That's the gist I get, both from replies here and things I've seen on other forums. The capacitance isn't critical but the high switching speed requires extremely low ESR. Why exactly that is I don't know.

--- End quote ---
Because resistance results in voltage drop and heat. For example adding 5 milliohms in series with 100A current means 0.5V voltage drop and 50W power dissipation. It's not about switching speed as such, it's about very high current at very low voltage. If you reduce converter switching speed, ESR still would need to be extremely low, however the more you reduce it, the more bulk capacitance will play a role.

StrayElectrons:
When I recapped my Dell 8300 Dimension back in the day, I used ultra low ESR capacitors and computer lived on daily use at work for about 5 years and was pulled still working.  And in same era of P4 boards, there were mixture of polymer and electrolytic capacitors as well.    Many people did all polymer mod for the VRM section and rest of board, with no issues as well due to lack of good ultra low ESR capacitors recently.

Cheers,

WhichEndToHoldTheIron?:

--- Quote from: wraper on January 16, 2025, 04:15:10 pm ---Because resistance results in voltage drop and heat. For example adding 5 milliohms in series with 100A current means 0.5V voltage drop and 50W power dissipation. It's not about switching speed as such, it's about very high current at very low voltage. If you reduce converter switching speed, ESR still would need to be extremely low, however the more you reduce it, the more bulk capacitance will play a role.

--- End quote ---
I've been reading up on ESR and ripple current and I think I understand that now (the combination of ESR with ripple current resulting in power dissipation).

The one thing I've not understood yet is the scenarios where too little ESR can be a problem (apparently stability in some types of circuit).

WhichEndToHoldTheIron?:

--- Quote from: StrayElectrons on January 16, 2025, 05:31:43 pm ---When I recapped my Dell 8300 Dimension back in the day, I used ultra low ESR capacitors and computer lived on daily use at work for about 5 years and was pulled still working.  And in same era of P4 boards, there were mixture of polymer and electrolytic capacitors as well.    Many people did all polymer mod for the VRM section and rest of board, with no issues as well due to lack of good ultra low ESR capacitors recently.

Cheers,

--- End quote ---
Thanks - that agrees with comments I've seen on other forums about the subject.

In combination with other comments in this thread I feel reasonably confident that polymer caps (with appropriate ESR and ripple current values) should be safe for the VRM sections on this board.

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