should OSTs in motherboard VRM sections always be replaced?

[mrmazda]

My ECS P965T-A has spent nearly the whole time since I bought it new over 6 years ago running OS/2. It's installed multiboot, so there is some running time in Linux and DOS. Quite some time ago already, maybe around 3 years, I replaced a very large number of 8mm caps on it, but not its 3 purple 10mmX25mm OST RLX 1500uf 16v. I no longer recall details, but suspect I had some bulgers and replaced everything of same specs with suitable low ESR replacements I had on hand at the time. As I use it constantly, I wanted it back in service without waiting on ordering what I didn't have. Doing what I did got it going.

Since then I acquired some Rubycon MCZ 1500uF 16v 10mmX20mm from Topcat, so when it started fritzing today, and based on the OST reputation here, I decided to install them without even thinking about what other than dust accumulation and overheating could be wrong. On removal I checked and found all 3 OSTs measured above 1500uF, with highest ESR of the three .01. The Rubys I put in measured ESR as high as .02, and uF as low as 1472. The board still has some smaller OSTs (100uV 6.3v) and G-Luxons (470uF 16v & 100uF 16v). I put it back together with just the 3 new, but the corrupt video output was at least as bad, maybe worse. Turns out a near twin "new" PCIe X600 Radeon fixed it.

These 3 OSTs seem to be far better than their reputation here. Should I commit them to the trash anyway? Save them for use in power supplies? Other?

[c_hegge]

Re: should OSTs in motherboard VRM sections always be replaced?

Their ESR specifications make them unsuitable for use in PSUs. Those 3 caps are used on the VRM high side - one of the least stressful areas of a motherboard. OST can sometimes be OK if they are not stressed.

[pc7fan]

Re: should OSTs in motherboard VRM sections always be replaced?

Agreed with you c_hegge - I've seen OST go bad in PSU's, especially in the 5Vsb section. They really despise heat AFAIK and just fail most of time without any physical signs. They're just fine in low heat & stress applications, I actually reuse them in other projects I build (not critical) if they test good for ESR & capacitor in the first place and I don't have any problems.

[stj]

Re: should OSTs in motherboard VRM sections always be replaced?

that's the ost weakness.
get them hot and they will be bloated in a year or 2 worst case.
keep them cool and you can get 20years from them - maybe more!!!