quicknick wrote on 2020-03-24, 13:42:

Hi everyone, […]
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Hi everyone,

Decided to build a system around this board:

EpoX P55-TX2.jpg

There are a lot of unknowns about the final configuration, but I'm aiming for a Riva128 PCI+ possibly dual VooDoo2 (if both my boards work).
The CPU will be a K6-2 at 400MHz (66x6.0).

The problem is related to the CPU voltage, as the board only offers 2.0 and 2.1 volts and then jumps to voltages that are inappropriate to a K6-2 (2.8, 2.9 and 3.2 volts).
I have a tray of 10 NOS K6-2-400AFRs that require 2.2 volts, do you think picking a random one and sticking it to the board will result in a stable system at 2.1 volts?
Tried to replace the voltage selection jumper with a resistor, used 100ohm to 1Kohm and nothing changes. Can't decipher the inner workings of this VRM.

EpoX P55-TX2_vrm.jpg

Of course it would be safer (stability-wise) to use a 500MHz K6-2, it should have no problems working at 400MHz with a slightly lower voltage, but I'd really like to use one of the NOS CPUs.
I also tried my only K6-2+ on the board. It works ok, but BIOS detects it as -MMX 66MHz and my OCD can't live with that 😀
(The K6-2 is detected as K6 3D, which I find nice).

I think most 2.2V K6 cpus will work fine at 2.1V - no underclocking necessary, but don't overclock. And yes, you should run programs with high cpu-load and test the stability to be on the safe side.
K6-III cpus requiring 2.4V will not work, there were also 550MHz ones requiring 2.3V which will be problematic, too.
A good test will be a 2.2V K6-2 500 at stock speed @2.1V, when that works stable you won't have any problems with 400MHz neither in my opinion.

Maybe the 2.1V setting results in 2.2V anyway, you would need to measure it. I would not worry about it, when it works. You don't take big risks with undervolting, the system could crash of course.

Thank you for the good suggestions. I think the 550MHz/2.3V one would work without a sweat at 400/2.1, but I don't have one.
I've already started "binning" the CPUs from that tray, running them on a SS7 platform at 500MHz/2.2V, so a 100MHz overclock. I found the Quake benchmark from Phil's pack to be the most demanding, so far from 5 CPUs tested there are 3 that seem to work at 500 (even played a few minutes of Quake on each) and 2 that are failing (game exits unexpectedly). I think the "good" ones will work ok at 400/2.1

The 2.1 setting on the board actually yields 2.132 which is encouraging.

Tried with no voltage jumpers at all and it remains at 2.074 - same as with the jumper on "2.0V". I don't dare testing combinations of 2 or more jumpers; this is my only full-ATX Socket7 board.

What I forgot to mention is that I'm looking for any suggestion regarding the rest of the build. Is the Riva128 too underpowered or the V2s in SLI too powerful for the K6-2/400?
Should I stick to 64MB RAM or go for full 256 knowing three quarters of it won't be cached?
What sound cards would fit the best this build? I have AWE64 both gold and value, ESS1868 with onboard wavetable, Sound Galaxy Waverider 32+ among others. Also, would a GUS classic (early 2.2 revision) be very out of place on a system like that?

Progressing slowly, but things are looking good.
Recapped the motherboard, cleaned, recapped and added -5V output to the Delta 250W PSU I had lying around, made some small mods to the case (either it or the motherboard are not exactly ATX standard and many of the mounting holes were in the air), repaired/modded the NEC-chipset USB2.0 card which looks like it had a hard life - missing SMD resistors, one USB connector badly burned - I removed the internal connector and replaced it with a header to be able to use at least one front panel USB.

The hard drive is a Barracuda ATA IV 40GB limited to 32 via the jumper, otherwise the board would hang at IDE detection. Very happy with its speed, wish I had something comparable back in the days 😀
But, how about this? UDMA5 on the PIIX4? This surely has to be a mistake. I used a 80-wire cable for the HDD, since i have plenty of them NOS, which can't be said about the 40-wire ones that are battered and worn.

Both Voodoo2 cards are in order, but getting a bit hot for my liking so more testing will be done after fitting a 120mm fan to the side panel. I used the FastVoodoo2 3.6 drivers but in the meantime found out there is a 4.0 version so I will update them tomorrow. (disregard that. I'm using v4.6 and I think it's the latest). Only tested 3dmark99 today, scores are 583 for the Riva128, 1425 (Voodoo2) and 1780 (V2 SLI). I was expecting nearly double in SLI vs. single, but perhaps I'm hitting the CPU limits. I know there's more tinkering to come, including testing with 64MB RAM or going all out with 256.

Still haven't decided about the sound card, but I'll probably go with the Aztech Sound Galaxy Waverider 32+.

More pics...

To be absolutely safe about data integrity, you may limit max HDD UDMA mode to UDMA2 by special tool. For Seagate it is UATA100.exe

http://www.autourdupc.com/Logiciel/Utils/Softs/UATA100.TXT