Oh, also should add that I tried two PSUs. One with 20A on 5v RAIL (modern eVGA PSU) and one with 30A on 5v rail (an old generic P4-era PSU)

The board revision would suggest it is a VM, not a VM/400. Though I don't know what difference there is (if any) apart from the bios

https://theretroweb.com/motherboards/s/asus-a … n8x-vm-rev-2-02

https://theretroweb.com/motherboards/s/asus-a7n8x-vm-400

The Image on TRW of the /400 version is too small to see the revision number. I will keep looking!

FullYes wrote on 2026-09-14, 11:18:

The board revision would suggest it is a VM, not a VM/400. Though I don't know what difference there is (if any) apart from the […]
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The board revision would suggest it is a VM, not a VM/400. Though I don't know what difference there is (if any) apart from the bios

https://theretroweb.com/motherboards/s/asus-a … n8x-vm-rev-2-02

https://theretroweb.com/motherboards/s/asus-a7n8x-vm-400

The Image on TRW of the /400 version is too small to see the revision number. I will keep looking!

Thanks for response!

Interestingly TRW image of the 2.02 revision has the same sticker on the parallel port as mine saying it is a A7N8X-VM/400

After looking a bit more, I think both models have the same board revision. Have you tried clearing the cmos?

FullYes wrote on 2026-09-14, 11:40:

After looking a bit more, I think both models have the same board revision. Have you tried clearing the cmos?

Yes, tried that. I forgot to mention. But thanks for suggestion.

I am wondering if maybe this board revision just isn't reliable at detecting 400mhz bus CPUs.

I guess the 3000+ isn't much slower. But ideally I wanted this to be 3200+.

I used to have a. A7N8X Deluxe back in the day with Barton 2500+ overclocked to 3200+ speed. I wish I never sold it. I still have my ATI All in Wonder 9700 Pro from that build though!

Make sure the resistor arrays on the cpu are not damaged.

RetroPCCupboard wrote on 2026-09-14, 12:11:

Yes, tried that. I forgot to mention. But thanks for suggestion. […]
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FullYes wrote on 2026-09-14, 11:40:

After looking a bit more, I think both models have the same board revision. Have you tried clearing the cmos?

Yes, tried that. I forgot to mention. But thanks for suggestion.

I am wondering if maybe this board revision just isn't reliable at detecting 400mhz bus CPUs.

I guess the 3000+ isn't much slower. But ideally I wanted this to be 3200+.

I had the A7N8X-X, great o/c'er!

The 3200+ was the one to have. I had a thoroughbred 2800+ back then (2.25GHz) so was clocked higher than the 3200+ but only had 256kb L2. It actually pretty well matched the 3200+ and with the FSB cranked up to 225MHz it was considerably faster (still running at 2.25GHz overall, as it didn't like higher clocks, just loved higher FSB)

I would offer to help with the 3200+ but I don't have anything that officially supports it. I just got one of these:

https://www.ebay.co.uk/itm/820071041743

But I think it only does 400FSB with overclocking. Which I will of course be trying 😁

Karbist wrote on 2026-09-14, 12:31:

Make sure the resistor arrays on the cpu are not damaged.

Thanks. I didn't notice anything. But will take off the cooler to check this evening.

FullYes wrote on 2026-09-14, 12:42:

I would offer to help with the 3200+ but I don't have anything that officially supports it. I just got one of these:

https://www.ebay.co.uk/itm/820071041743

But I think it only does 400FSB with overclocking. Which I will of course be trying 😁

Yeah, doesn't look like it officially goes up to 400mhz. Will be Interesting. Not a bad price for a new board.

Hmm. Well it seems like the motherboard isn't posting at all now. No signs of life on POST analyser card. I have tried 3200+ and 3000+. Nothing. 🙁

Have you got a lower power CPU to try? any beeps? PSU voltages OK? Your 30A 5v should be alright but the 20A I would say is marginal at best.

FullYes wrote on 2026-09-15, 08:50:

Have you got a lower power CPU to try? any beeps? PSU voltages OK? Your 30A 5v should be alright but the 20A I would say is marginal at best.

Ok. Well, I checked PSU voltages. They look within spec. 12.2v and 5.08v. There are no beeps at all.

So I tried another motherboard Abit KD7. That already had a 333Mhz 3000+ in. It booted ok. I then put in the other 333mhz bus 3000+ that wouldn't boot in the A7N8X-VM/400. It booted straight away. So at least that's ok.

I then put in the 400mhz bus 3200+. The motherboard doesn't officially support it, but I would have thought it should at least boot. But, no, nothing. Even worse I put back the 3000+ and now the motherboard wont post. It won't post with either 3000+.

So I think this means the 3200+ has now killed both motherboards. Do you agree?

Oh dear! I guess you could test the 3200+ CPU for shorts to confirm? I would have thought you would smell the magic smoke escaping in such a situation.

You could also run a modern PSU on a KD7 to rule out any issues there, assuming it's the same as this?

https://theretroweb.com/motherboards/s/abit-ab-kd7-s

How do the CPU dies look?

I would say that a 3200+ should work in any board that has support for Barton CPUs, it may just not run at full speed. So I don't think you did anything wrong. I certainly would have tried it. I am running a Barton XP-M 2800+ in a much older KT133A based board and it works just fine - I patched the bios to recognise the CPU but I also ran a 2600+ without the patch - other than the bios recognising the CPU during POST, it made no other difference.

FullYes wrote on Today, 07:35:

Oh dear! I guess you could test the 3200+ CPU for shorts to confirm? I would have thought you would smell the magic smoke escapi […]
Show full quote

Oh dear! I guess you could test the 3200+ CPU for shorts to confirm? I would have thought you would smell the magic smoke escaping in such a situation.

You could also run a modern PSU on a KD7 to rule out any issues there, assuming it's the same as this?

https://theretroweb.com/motherboards/s/abit-ab-kd7-s

How do the CPU dies look?

Thanks for the reply. Looks like the KD7 is ok after all. I put in POST analyser card and I could see that it was going through some kind of loop. So not completely dead like the A7N8X-VM. I wasnt sure what the codes mean, so I just tried reseating the RAM and GPU and now it boots with both of the 3000+ CPUs. I guess I must have knocked something when swapping CPU.

Anyway, when I put the 3200+ in the KD7, there are no POST codes showing on the analyser card. So, I am not sure what this means. It doesn't officially support the CPU, but it does support 333Mhz Bartons. It should boot the 3200+ shouldn't it? Even if at a lower speed. When I first put in the 3000+, after clearing CMOS, it is initially recognised as a 2500, and I just have to set the speed to 3000+ in the BIOS. I was expecting the 3200+ to do similar.

I am thinking maybe this CPU has an issue and I should return it. Unless I risk keeping it and try to source another motherboard that supports it. But I have kind of lost enthusiasm for this CPU now. Wondering if it is worth the trouble when I already have a working 3000+.

Oh, and I think the CPU looks ok. There was no puffs of smoke or popping of silicon.

Actually, just thinking, I do have a Barton 2500+. That has same muliplier and voltage as the 3200+. Only difference is the bus speed. So I guess I could try it and see what that does.

RetroPCCupboard wrote on Today, 07:53:

Thanks for the reply. Looks like the KD7 is ok after all. I put in POST analyser card and I could see that it was going through […]
Show full quote

FullYes wrote on Today, 07:35:

Oh dear! I guess you could test the 3200+ CPU for shorts to confirm? I would have thought you would smell the magic smoke escapi […]
Show full quote

Oh dear! I guess you could test the 3200+ CPU for shorts to confirm? I would have thought you would smell the magic smoke escaping in such a situation.

You could also run a modern PSU on a KD7 to rule out any issues there, assuming it's the same as this?

https://theretroweb.com/motherboards/s/abit-ab-kd7-s

How do the CPU dies look?

Thanks for the reply. Looks like the KD7 is ok after all. I put in POST analyser card and I could see that it was going through some kind of loop. So not completely dead like the A7N8X-VM. I wasnt sure what the codes mean, so I just tried reseating the RAM and GPU and now it boots with both of the 3000+ CPUs. I guess I must have knocked something when swapping CPU.

Anyway, when I put the 3200+ in the KD7, there are no POST codes showing on the analyser card. So, I am not sure what this means. It doesn't officially support the CPU, but it does support 333Mhz Bartons. It should boot the 3200+ shouldn't it? Even if at a lower speed. When I first put in the 3000+, after clearing CMOS, it is initially recognised as a 2500, and I just have to set the speed to 3000+ in the BIOS. I was expecting the 3200+ to do similar.

I am thinking maybe this CPU has an issue and I should return it. Unless I risk keeping it and try to source another motherboard that supports it. But I have kind of lost enthusiasm for this CPU now. Wondering if it is worth the trouble when I already have a working 3000+.

Yeah I would expect it to work in that board - just at the wrong frequency. In fact it'd probably list it as a barton 2500+ as you say it's the same multiplier as the 3200+ just at the 333MHz FSB instead of 400

Could you post a high res pic of your cpu? Fakes were everywhere back in the day.
In my experience:
1. always put thermal paste
2. always use a heatsink and be it latched to the socket, not just "on the core"; thing rises high fast in temp and can fry;
3. if it fails posting: unplug power and wait a couple of minutes; if still not posting, remove all cards and put them back; many boards behave like this;

This is why I don't have any system with that cpu in my builds list. If you make a mistake there is no forgiveness for you.
Socket 462 is not an easy chap to deal with.