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Help overclocking an AMD 5x86 133

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First post, by squelch41

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Hi,
I am trying to overclock my 5x86 but keep failing!
It runs fine at the stock 133MHz but if I move the bus speed up to 40MHz, it is unstable.
It will POST and I can get to a dos prompt if I dont load the ESS cdrom driver (usually crashes if I do).
Pretty sure it is an ADZ varient but there is a heatsink on it so cant quite remember!

I can run speedsys 4.78 and 3D bench from PhilsComputerLab DOS benchmark pack.
However, if I run eg Duke3d, I often get protection faults as it loads the DOS extender or, I get to the loading screen and then it crashes.

I have tried:
Setting the cache to the slowest setting in bios
Setting RAM to slowest setting.
Setting ISA clock speed to bus/5 (so 8MHz)
Setting the jumpers on the motherboard at positions 33 and 34 to >33MHz bus speeed and +1WS for VLB
I have also tried disabling the L2 cache but that doesnt make any difference.

The PSU 5v voltage is 4.7v measured on the ISA slot and the output from the voltage regulator on the board to the cpu is 3.4v and these remain stable under load. (ATX power supply with AT adapter)

I have a heat sink with a case fan blowing across it - it doesnt seem particulaly warm to the touch.
I have tried adding a heat sink to the chipset controller and also to the cirrus VGA chip.
The ram doesnt get hot and I have tried just with a single 32mb stick rather than 32mbx2

I was wondering if -
The VLB vga card could be the issue? Not sure how I'd tell (and presumably if unstable just starting up in DOS, this isnt so likely?)
There is another avenue I am not seeing

Or does it just seem that the CPU cant manage 160MHz (though looking online, it seems that pretty much all of them are?)

Would be grateful for advice.
Full system spec in signature.

V4P895P3 VLB Motherboard AMD 486 133MHz
64mb RAM, CF 4Gb HDD,
Realtek 8019 ethernet + XT-IDE bios ROM, ES1869 soundcard, VLB Cirrus Logic GD5428 1mb VGA

440bx MSI 6119, modified slocket , Tualitin Celeron 1.2Ghz 256mb SD-RAM, CF 4GB HDD, FX5200 gfx

Reply 1 of 8, by debs3759

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It sounds to me like you lost the CPU lottery, as you appear to have tried everything else.

See my graphics card database at www.gpuzoo.com
Constantly being worked on. Feel free to message me with any corrections or details of cards you would like me to research and add.

Reply 3 of 8, by schlomoe99

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rmay635703 wrote on 2020-11-18, 17:10:

Some motherboards/cards aren’t stable at 40mhz and need different settings or even in some cases different cache

I agree here. Have you tried switching from Write-Back cache to Write-Through cache in the BIOS?

Reply 4 of 8, by The Serpent Rider

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(though looking online, it seems that pretty much all of them are?

ADZ =/= better overclocking. ADZ can officially operate stable at higher temperatures and that's about it. If you can, increase voltage to 4V and it most likely will boot.

I must be some kind of standard: the anonymous gangbanger of the 21st century.

Reply 5 of 8, by PC-Engineer

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Three guesses from my side:

1. If you have a VLB IDE controller replace it with an ISA type. The VLB is not specified for two cards @40MHz. It is difficult to find a combination of cards, board and CPU which is running stable at 40MHz.
2. replace the Power supply or at least the capacitors at the output of it.
3. deactivate the 2nd level cache in bios and try it again. If it runs, then you have a defective cache chip.

Epox 7KXA Slot A / Athlon 950MHz / Voodoo 5 5500 / PowerVR / 512 MB / AWE32 / SCSI - Windows 98SE

Reply 6 of 8, by squelch41

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schlomoe99 wrote on 2020-11-18, 19:56:
rmay635703 wrote on 2020-11-18, 17:10:

Some motherboards/cards aren’t stable at 40mhz and need different settings or even in some cases different cache

I agree here. Have you tried switching from Write-Back cache to Write-Through cache in the BIOS?

Hmm, no I haven't. Though disabling the L2 cache all together made no improvement.
Will try though - jumper flipping on this board rather than a bios setting sadly!

V4P895P3 VLB Motherboard AMD 486 133MHz
64mb RAM, CF 4Gb HDD,
Realtek 8019 ethernet + XT-IDE bios ROM, ES1869 soundcard, VLB Cirrus Logic GD5428 1mb VGA

440bx MSI 6119, modified slocket , Tualitin Celeron 1.2Ghz 256mb SD-RAM, CF 4GB HDD, FX5200 gfx

Reply 7 of 8, by adalbert

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The Serpent Rider wrote on 2020-11-18, 20:25:

ADZ =/= better overclocking. ADZ can officially operate stable at higher temperatures and that's about it. If you can, increase voltage to 4V and it most likely will boot.

Yeah, I once bought ADZ for overclocking, just to find out that my ADW worked fine on 160MHz, while ADZ did not.

Repair/electronic stuff videos: https://www.youtube.com/c/adalbertfix
ISA Wi-fi + USB in T3200SXC: https://www.youtube.com/watch?v=WX30t3lYezs
GUI programming for Windows 3.11 (the easy way): https://www.youtube.com/watch?v=d6L272OApVg

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