Do you have a diagnostic card? Also are you 100% sure that the CPU is in working state?

Please note, the K6/2+ is a laptop cpu, manufactured on different node than the normal k6/2. So its not just differs in cache, it differs in many ways. Might or might not works in a random desktop board. Its recommended to do a bios upgrade, which could fix your problems.

I didn't check the Biostar, but Jan has a patched BIOS with K6-2+ support for the Tyan (assuming that the S1590 is the same as the S1590S) on his page. Upgrade your BIOS to that, then try again. http://www.steunebrink.info/k6plus.htm

Do you have a diagnostic card? Also are you 100% sure that the CPU is in working state?

No, and yes. Sent it to a friendly member from oure german dos board, who testet it for me.

Its recommended to do a bios upgrade, which could fix your problems.

I have the latest regular one on the M5ALA Board, and a the latest mod-version (or patched) on the Tyan Board.

I'm out of ideas. I`ll try more voltage on the tyan Board. (2,1.V).
Maybe the M5ALA is simply not compatible and the Tyan board has problems with the 2.0V setting?

Some motherboards that don't have BIOS support for the K6 plus CPUs will POST and display "MMX CPU 66 MHz" or something similar, but some will not POST at all. That neither board will POST with this CPU makes me a bit nervous, especially since one of them has the correct BIOS. Do experiment with the core voltage setting (2.2 is no problem), and here is a thread that goes over possible voltage settings on that board: Tyan S1590 (baby-AT Super7) 3.3v AGP power limits (TLDR: you're best off using an ATX power supply)

The last official BIOS for the Tyan S1590 supports the K6-III, but not the "+" CPUs. The modded BIOS that adds support for the K6-2+ says something like version "J.2" on the POST screen. If that's the version you have then it should be working. I've used a K6-3+ with that BIOS, and I think a 2+ also.

There are 2 ways to set 2.0V with the jumpers, and I'm not sure if both of them work. They're listed in that overly long post that Repo Man linked to.
There are several revisions of the S1590 so it's possible yours is different.

With your M5ALA - if it powers up with 1 CPU, but then won't even power up with the K6-2+ inserted, that seems concerning. It makes me wonder if the CPU is shorted, or perhaps it just doesn't like something about the jumper settings you're using with it. I have no idea if that board can support the 2+ but it should at least turn on.

Demolition-Man wrote on 2023-09-16, 18:07:

Hi! I found a cheap K6-2+ 500 ACZ CPU. The CPU could now be tested outside and works, just not for me. Just why? I tested two mo […]
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Hi!
I found a cheap K6-2+ 500 ACZ CPU. The CPU could now be tested outside and works, just not for me.
Just why? I tested two motherboards. First a Biostar M5ALA running a K6-2 500. So just changed the voltage, only 2.1V/3.3V is possible but nothing, not even the CPU fan turns?
Does anyone here have an idea what the problem could be?
Thanks and regards!

Yes I have an idea about the problem: Do you know what motherboard they tested it on ???
I won't go into the nutz and boltz but there are topics here all about the + cpu's with lots of people having issues on desktop boards......just sayin

Sorry was busy.
Bios Version on the Tyan S1590S Board is :
B1.16C J.1, 10/27/2000-
Is this the right one?

The CPU will be send to me back in a few days, then i will give it another try. Only on this board. But than the only option remaining, is to sell that thing. 😉
And look for a (of course really expensive) faster K6-III. I`m not a big fan of overclocking.

Do you know what motherboard they tested it on ???

I`m asking right now.
Edit:
PCChips M577

Demolition-Man wrote on 2023-09-17, 15:02:

Sorry was busy. Bios Version on the Tyan S1590S Board is : B1.16C J.1, 10/27/2000- Is this the right one? […]
Show full quote

Sorry was busy.
Bios Version on the Tyan S1590S Board is :
B1.16C J.1, 10/27/2000-
Is this the right one?

The CPU will be send to me back in a few days, then i will give it another try. Only on this board. But than the only option remaining, is to sell that thing. 😉
And look for a (of course really expensive) faster K6-III. I`m not a big fan of overclocking.

Do you know what motherboard they tested it on ???

I`m asking right now.
Edit:
PCChips M577

Yes, the B1.16c - patch J.1 10/27/2000 - BIOS for the Tyan S1590 is the one you need for K6-2+/III+ support.
This was the very first socket 7 BIOS I patched and I'm still using it on my S1590 board, first with a K6-2+/450 and the past 15 years running a K6-III+/550 at 600 MHz! 😀

Note that older S1590 revisions have a different Vcore controller with 4 Vcore jumpers. On these boards the 2.0V setting only gives you 1.2V so you have to use the 2.1V setting for your K6plus. The later 5 Vcore jumper S1590 boards don't have this problem and can be set at 2.0V Vcore.

Cheers, Jan

I don't know if the following helps with something, but I had similar POST issues with a K6-2+/450ACZ CPU on a Gigabyte GA-586ATV motherboard. The last two official BIOSes for it (1.28 causes restart loops and with 1.23 it doesn't perform POST) nor the modded one from Jan's website (based on 1.28) didn't work for me.

Had to downgrade the BIOS to version 1.22 for this combination to work, with some cajoling regarding HDD capacity size.

Thank You.
I'll try again soon, with the 2.1V setting.
@Chkcpu
I knew its your patch, thx again, great work.
I found a cheap K6-III 450 AFX, i prefer the K6-III CPUs because of the larger cache.
The onboard L2 Cache doesnt work anymore.
I still don't understand the K6 tools. Which ones do I need and what can they do? I don't actually need overclocking, quite the opposite. Only 50 MHz more, but now there are division zero errors. At Monkey Island for example
I don't think slowdown works.

Demolition-Man wrote on 2023-09-23, 20:47:

I still don't understand the K6 tools. Which ones do I need and what can they do? I don't actually need overclocking, quite the opposite. Only 50 MHz more, but now there are division zero errors. At Monkey Island for example

The only essential tools for the K6plus CPU are:

• SetMul: Can change the CPU multiplier from x2.0 to x6.0 (excluding x2.5) on the fly in addition to the ability of toggling both L1 and L2 cache.
• K6INIT: Used to enable optimizations such as write allocate and write combining for some speedup.

Edit: It actually a regular K6-III CPU, so adjusting the CPU multiplier with software won't work. 😜

Gmlb256 wrote on 2023-09-21, 14:21:

I don't know if the following helps with something, but I had similar POST issues with a K6-2+/450ACZ CPU on a Gigabyte GA-586ATV motherboard. The last two official BIOSes for it (1.28 causes restart loops and with 1.23 it doesn't perform POST) nor the modded one from Jan's website (based on 1.28) didn't work for me.

This is probably not helpful either but I have a Gigabyte GA-586T2 here that seems to have trouble with a K6-2+ 450 when using Jan's modded BIOS for that board. This is strange because I have another GA-586T2 that does work with the modded BIOS and the exact same K6-2+ CPU, and the only different b/w these 2 boards is the revision. The working one is rev1.2, and the non-working one is rev1.5.

I hadn't thought of increasing the vcore, I'll try it at 2.1v.

Demolition-Man wrote on 2023-09-23, 20:47:

I found a cheap K6-III 450 AFX, i prefer the K6-III CPUs because of the larger cache. The onboard L2 Cache doesnt work anymore. […]
Show full quote

I found a cheap K6-III 450 AFX, i prefer the K6-III CPUs because of the larger cache.
The onboard L2 Cache doesnt work anymore.
I still don't understand the K6 tools. Which ones do I need and what can they do? I don't actually need overclocking, quite the opposite. Only 50 MHz more, but now there are division zero errors. At Monkey Island for example
I don't think slowdown works.

(as gmlb mentioned, the reclocking tools don't work on the original K6-III, only the "+" chips)

If you got your original K6-III to run 500MHz usably at all, then you have a better chip than mine.
I'll be very surprised if you can get it truly stable at that speed. The original K6-III is pretty much done at 450MHz. At 500Mhz and increased Vcore, I'm not sure if the motherboard can even handle the power draw you'd be dealing with.

My K6-III 450Mhz (marked as a 2.2V) can't even run it's own rated clock speed unless the voltage is bumped to 2.3V. Even after recapping the motherboard (S1590), it's prone to rare glitchiness with that CPU. I'm not sure if I have a bad CPU or the board doesn't like it's power draw, but it never felt more than 99% reliable.
As soon as I tried a "+" chip, I was won over immediately. They use less power and clock up so easily that even a K6-2+ ends up faster.
But if you can't get the "+" to work, then the original K6-III is a good 2nd option, but I wouldn't expect more than 400-450MHz out of it with any reliability.

Thanks for the feedback!
I can't modify anything on the PC at the moment, because I injured myself while cycling.
The only thing I can do at the moment is to continue testing the "new"K6-III CPU. But it works. Sysmon always shows 2.36V maybe that's why. The two smal brackets on the socket have broken off, so I'm having problems with the cooling sometimes. I therefore avoid overclocking. A K6-III+ is very rare here in Germany and way to expensive.
But I still want to know whether the K6-2+ works for me and what benchmark results it delivers. Permanently switching to the K6-2+ CPU, I don't know if I would do that. I have such a beautiful K6-III sticker on the case. 😉
We'll see then, but it might take a while.

Edit: My old 2,4V K6-III 400 is now working with the M5ALA Boards without any problems.

Ok, I'm just impatient.
And yes 2.1V does the trick. Thank you!
But...
What about the K6-2+ vs. K6-III story? Who is spreading false information?
No 4% difference. The K6-III beat the 50 MHz faster K6-2+ in almost every Dosbench benchmark.
I'm still testing under Windows 98. SiSoft Sandra 99, 3DMark 99 and 3DMark 2000. I'm curious. Later.

Edit: Ok disappointment. The K6-III is simply better.
A lot of work for this conclusion.

Do you want to see the benchmark results, or do you believe me? 😉

Demolition-Man wrote on 2023-09-30, 14:15:

What about the K6-2+ vs. K6-III story?

K6-2+ vs K6-III was more about flexibility when slowing down the computer and efficiency which the former shines. Absolute performance is a different story.

Who is spreading false information?

Not me. 😉

I never said that K6-2+ is faster than K6-III or K6-III+.

I never said that K6-2+ is faster than K6-III or K6-III+.

I didn't want to blame anyone. Everything is ok, you just have to test things like that yourself. 😀

A K6-2+ 500 (@ stock) is not a bad cpu. Roughly in the same performance class as a K6-III 400.

Chkcpu wrote on 2023-09-21, 09:25:

Yes, the B1.16c - patch J.1 10/27/2000 - BIOS for the Tyan S1590 is the one you need for K6-2+/III+ support. This was the very […]
Show full quote

Demolition-Man wrote on 2023-09-17, 15:02:

Sorry was busy. Bios Version on the Tyan S1590S Board is : B1.16C J.1, 10/27/2000- Is this the right one? […]
Show full quote

Sorry was busy.
Bios Version on the Tyan S1590S Board is :
B1.16C J.1, 10/27/2000-
Is this the right one?

The CPU will be send to me back in a few days, then i will give it another try. Only on this board. But than the only option remaining, is to sell that thing. 😉
And look for a (of course really expensive) faster K6-III. I`m not a big fan of overclocking.

Do you know what motherboard they tested it on ???

I`m asking right now.
Edit:
PCChips M577

Yes, the B1.16c - patch J.1 10/27/2000 - BIOS for the Tyan S1590 is the one you need for K6-2+/III+ support.
This was the very first socket 7 BIOS I patched and I'm still using it on my S1590 board, first with a K6-2+/450 and the past 15 years running a K6-III+/550 at 600 MHz! 😀

Note that older S1590 revisions have a different Vcore controller with 4 Vcore jumpers. On these boards the 2.0V setting only gives you 1.2V so you have to use the 2.1V setting for your K6plus. The later 5 Vcore jumper S1590 boards don't have this problem and can be set at 2.0V Vcore.

Cheers, Jan

I came here to also ponder the 1.2v possibility.

Seconded.

Edit: reading it seems that was it! Woohoo!

There are a number of differences between the + cpus and the III cpus

The + is a smaller process requiring less voltage and uses less wattage.

The + cpu also has the ability for software multiplier control

Past that they perform basically the same at equal clocks. But the + can overclock higher.

The 2+ can sometimes be modded to a 3+ by the way.