I don't know any specific MicroATX board models to suggest, but:

bjt wrote:

I'm going to try to get a NOS board to avoid further capacitor problems.

Surprisingly NOS doesn't really preclude cap problems. The faulty chemistry of some bad caps can lead to them bulging and leaking even if they've never been powered. I've seen several independent stories of people buying sealed NOS motherboards and finding the caps bulged inside the sealed bag. Even if they arrive intact, they might not last long.

Generally I would suspect that popular models of overclocking friendly motherboards would be the most likely to have had any updates that were necessary to make the CPUs boot, and they will let you manually set the multiplier and voltage as necessary. I don't know specific MicroATX models though.
When I used a mobile chip on an ABit AN7 (full ATX nForce2) it defaulted to a much higher voltage than needed so it was good to be able to adjust it downward. I don't know if that's a common problem or not.

For making manual adjustments I love the flexibility of ABit boards, but they had crap caps up until the late nForce2 boards. Honestly I don't know who (if anybody) was consistently using good caps on mid-life Athlon motherboards that would have universal AGP. Maybe Asus, but I'm not sure about that. KT266A and KT333 are I think the last chipsets to typically have universal AGP slots.

shamino wrote:

Surprisingly NOS doesn't really preclude cap problems.

Yep, I understand. Just trying to dodge the bullet in that a NOS, decent quality board will give me the best chance of a stable system.
Might ditch the Universal AGP requirement in that case and get something like an Asus a7(s/v/n)8x-m. These come in VIA KT400, SIS 741GX and NForce 2 flavours.
Am I right in thinking the NForce 2 is the most likely to have multiplier and voltage control in the BIOS?

It really comes down to luck on the caps, I have an Asus A7V333 board here, all the CPU VRM caps are Nichicon and Rubycon stuff, but the other caps are OST. Still, not one of them has bulged yet and the board works perfectly, has universal AGP too. Micro ATX, I don't know that well, but I have several working Asus made MATX boards for HP computers with Nforce2 chipsets, just cannot remember the model right now. Those HP oem boards are nice in that atleast some of them let you flash a different Asus board bios on them and unlock voltage options and overclocking.

I ended up with a great condition Gigabyte GA-7VASMFS. Ran it for a few days and it's shaping up to be a great board.
VIA KT600, AGP, 3 PCI slots. No onboard video.
Nichicon caps all around and no sign of bulging.

The only negative is that it won't support 3.3V-only AGP cards and because it's a OEM board for Fujitsu Siemens the BIOS is fairly barebones.
However, I found most of the missing options can be unhidden by pressing CTRL-F1.

CPU wise, I decided not to get a low-voltage mobile chip because I understand that they default to 6X multiplier on desktop boards and many boards will overvolt them as well, meaning they end up dissipating as much heat as a desktop chip anyway. Most people seemed to use them for overclocking on Nforce2 back in the day, which I'm not interested in.

Instead, looking on CPU World I saw that a few of the slower Thoroughbred XP desktop chips run at 1.5V and I tracked down a 1.5V 1700+ chip with a TDP in the low 40s rather than the 60w+ that most Athlons dissipate. This is running great on the Gigabyte board and noticably cooler than my old Thunderbird 1200.

I'm running it with a Ti4200, Voodoo3 PCI, Vortex 2 and soon to try putting an Audigy in there for EAX support too.

If I was you I avoid xp-m, they mostly have been run at the limit, either in a laptop or as an over lockers toy, I'd instead look at the socket a semprons. Low demand + low power demands. Look at Sempron 2200,2400

Socket A procs are often pretty cheap sometimes you can get them by the pound/kilo if you desire 🤣 but good luck with finding nos that doesn't have bad caps as shops ended up learning the hard way back in the day. Just keep looking for boards and eventually you will find a few that will meet your needs without breaking the bank and it is best to get one or two spares if something goes wrong. As for mobiles it can be hit or miss but I think that it is worth the risk if the price is low enough unless the seller has that vibe of being someone who is like ourselves then you probably should be cautious.

candle_86 wrote:

If I was you I avoid xp-m, they mostly have been run at the limit, either in a laptop or as an over lockers toy, I'd instead look at the socket a semprons. Low demand +low low power demands. Look at Sempron 2200,240

Yep which is why I recommend the 1.5v Thoroughbred desktop chips. 1700+ has a TDP in the low 40s and no compatibility issues. Very cheap on eBay too, just search for chips with code ending DLT3C.

bjt wrote:

candle_86 wrote:

If I was you I avoid xp-m, they mostly have been run at the limit, either in a laptop or as an over lockers toy, I'd instead look at the socket a semprons. Low demand +low low power demands. Look at Sempron 2200,240

Yep which is why I recommend the 1.5v Thoroughbred desktop chips. 1700+ has a TDP in the low 40s and no compatibility issues. Very cheap on eBay too, just search for chips with code ending DLT3C.

those were also OC favorites, I had one as high as 2.4GHz at some point with some serious overvolt (but my usual choice was 2.2GHz 1.7v or something like that)

don't the semprons have the multiplier locked? I would try buying an AXP with unlocked multiplier, it's much easier to set, specially if you are going to use it with a lower FSB chipset.

bjt wrote:

My Micro ATX Athlon Thunderbird build hasn't been too healthy lately. Regular hard locks which went away when the machine was wa […]
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My Micro ATX Athlon Thunderbird build hasn't been too healthy lately. Regular hard locks which went away when the machine was warmed up, a classic sign of bad caps I believe. No surprise considering that the board was ECS with some very dubious capacitors. I've tried recapping it but I just can't get enough heat into the board with my 50W iron around the VRMs - some big ground planes I think sinking the heat.

The machine ran very hot as well but was otherwise great for late 90s Win98 games and hosted a GF3, Voodoo 3 PCI, Monster Sound MX300 and DB50XG. I'd like to take this opportunity to refresh it and was attracted by the mobile Athlon XP CPUs, as these should run a lot cooler.

Any recommendations for Micro ATX boards supporting these CPUs? I understand it may be necessary to change to multiplier from the default 6X in software after boot, which is fine.
I'm going to try to get a NOS board to avoid further capacitor problems. Which chipsets are best, would KT266 work? KT266 has a universal AGP slot which would be nice to test older AGP cards. I have a NOS GF4 Ti4200 to go with a new board too.

I know you didn't ask for help with this here, but try preheating the board to 130-150 deg C with a heat gun before desoldering the caps. Heat it from the back side, and be careful with any plastic details. Use an IR thermometer to keep track of the temperature while heating.

Aideka wrote:

It really comes down to luck on the caps, I have an Asus A7V333 board here, all the CPU VRM caps are Nichicon and Rubycon stuff, but the other caps are OST. Still, not one of them has bulged yet and the board works perfectly, has universal AGP too...

Yeah, it's down to luck. I had an A7V333 with bad VRM caps. It died shortly after.

SPBHM wrote:

bjt wrote:

candle_86 wrote:

If I was you I avoid xp-m, they mostly have been run at the limit, either in a laptop or as an over lockers toy, I'd instead look at the socket a semprons. Low demand +low low power demands. Look at Sempron 2200,240

Yep which is why I recommend the 1.5v Thoroughbred desktop chips. 1700+ has a TDP in the low 40s and no compatibility issues. Very cheap on eBay too, just search for chips with code ending DLT3C.

those were also OC favorites, I had one as high as 2.4GHz at some point with some serious overvolt (but my usual choice was 2.2GHz 1.7v or something like that)

don't the semprons have the multiplier locked? I would try buying an AXP with unlocked multiplier, it's much easier to set, specially if you are going to use it with a lower FSB chipset.

Yes its locked but its a 333 bus CPU so its easy to support aswell

kaputnik wrote:

I know you didn't ask for help with this here, but try preheating the board to 130-150 deg C with a heat gun before desoldering the caps. Heat it from the back side, and be careful with any plastic details. Use an IR thermometer to keep track of the temperature while heating.

Thanks, yeah I need to get some better tools before I attempt another MB recap.