VOGONS


First post, by SVslw

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Hey everyone. A time ago I got K6-2+/550 for 30$ and was very happy of this 27 year old CPU. I modded it into K6-III+/550 and it worked fine! It booted and was identified as K6-III.
Once, when I tried booting again (no problems before), the cooler was a bit raised and didn't touch the IHS of K6 aaand..it didn't boot. The 4 digit PCI post card gave me C5 and C3 error. I tried booting from Pentium MMX 200 on the motherboard with the same RAM...it worked
Specs:
- Lucky Star 5MVP3 rev 2.0 (1mb cache version)
- K6-2+/550 modded to K6-III+/550
- 384 MB PC133 SDRAM
- PCI Diamond Stealth II S220 (Rendition Verite)

I really don't want to accept that I fried this CPU or broke it. Definitely not..I hope. Is there anything I can do?

Last edited by SVslw on 2025-02-18, 07:31. Edited 3 times in total.

Reply 1 of 9, by SVslw

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It should theoretically boot without cooler at all, but I don't know. I didn't overclock K6 this boot and previous boots, but have overclocked it before and returned to default frequency.

Reply 2 of 9, by Nemo1985

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I suppose that when it didn't boot you turned off the machine quick enough. Such short time without heatsink shouldn't have killed the cpu.

Reply 3 of 9, by bloodem

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SVslw wrote on 2025-02-18, 07:22:

Once, when I tried booting again (no problems before), the cooler was a bit raised and didn't touch the IHS of K6 aaand..it didn't boot. The 4 digit PCI post card gave me C5 and C3 error.

I would not expect to see any post codes with a fried CPU, the typical behavior would be "- - - -" on the post card.
Do you have any other boards that you can test it with?

2 x PLCC-68 / 4 x PGA132 / 5 x Skt 3 / 1 x Skt 4 / 9 x Skt 7 / 12 x SS7 / 1 x Skt 8 / 14 x Slot 1 / 6 x Slot A
5 x Skt 370 / 8 x Skt A / 2 x Skt 478 / 2 x Skt 754 / 3 x Skt 939 / 7 x LGA775 / 1 x LGA1155
Current PC: Ryzen 7 9800X3D
Backup: Ryzen 7 5800X3D

Reply 4 of 9, by SSTV2

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Partially working CPU is a sign of damage from overheating or prolonged overvoltage. I have two such CPUs, one was damaged by overvoltage, the other by a poorly mounted heatsink, which made only a partial contact with the CPU die (heatsink tilt). Both CPUs are functional enough for an early initialisation, but doesn't complete the POST. The overheated CPU initially ran at a lower frequency, but quickly failed to its current state because it received maximum voltage from a faulty VRM, which I did not identify in time.

In conclusion - it's dead, Jim.

Reply 5 of 9, by AlexZ

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Yup it's dead. You need to at least hold heatsink by hand on the CPU die to have it survive.

Pentium III 900E, ECS P6BXT-A+, 384MB RAM, GeForce FX 5600 128MB, Voodoo 2 12MB, Yamaha SM718 ISA
Athlon 64 3400+, Gigabyte GA-K8NE, 2GB RAM, GeForce GTX 260 896MB, Sound Blaster Audigy 2 ZS
Phenom II X6 1100, Asus 990FX, 32GB RAM, GeForce GTX 980 Ti

Reply 6 of 9, by Nunoalex

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Can you try to run it at a lower frequency ?

Reply 8 of 9, by mkarcher

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SVslw wrote on 2025-02-18, 07:22:

Hey everyone. A time ago I got K6-2+/550 for 30$ and was very happy of this 27 year old CPU. I modded it into K6-III+/550 and it worked fine! It booted and was identified as K6-III.
Once, when I tried booting again (no problems before), the cooler was a bit raised and didn't touch the IHS of K6 aaand..it didn't boot. The 4 digit PCI post card gave me C5 and C3 error. I tried booting from Pentium MMX 200 on the motherboard with the same RAM...it worked

C3 and C5 are status/error codes during BIOS decompression (as you might be aware: BIOSes at that time contain a boot block, and the remaining part of the BIOS is compressed like an LHA archive and decompressed into shadow RAM by the boot block, or a boot block "plugic" called a "decompression BIOS"). Issues at that stage are often memory issues. When you went down from the K6-III+ at 550MHz to the P-MMX at 200 MHz, you did not only reduce the CPU clock, but also dropped the FSB clock from 100MHz to 66MHz. If the RAM is marginal, the FSB drop might be the actual change that made the system work - so:

SVslw wrote on 2025-03-12, 13:16:
Nunoalex wrote on 2025-02-20, 15:30:

Can you try to run it at a lower frequency ?

Hmmm. Gonna try that

If you try that, don't try something like 100*3, but definitely stay at 66*something.

Reply 9 of 9, by tauro

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mkarcher wrote on 2025-03-12, 21:20:

C3 and C5 are status/error codes during BIOS decompression (as you might be aware: BIOSes at that time contain a boot block, and the remaining part of the BIOS is compressed like an LHA archive and decompressed into shadow RAM by the boot block, or a boot block "plugic" called a "decompression BIOS"). Issues at that stage are often memory issues. When you went down from the K6-III+ at 550MHz to the P-MMX at 200 MHz, you did not only reduce the CPU clock, but also dropped the FSB clock from 100MHz to 66MHz. If the RAM is marginal, the FSB drop might be the actual change that made the system work - so:

Interesting bits of info