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Amigaz
May 2nd, 2008, 03:20 AM
Have recently aquired this AST machine
http://www.ari-service.com/blender/cache/501549-005.htm

It was originally fitted with a Cyrix Cx486DX2-50 CPU which I've replaced with a Intel 486DX 75mhz overdrive CPU

I have two spare AMD 486DX4 100mhz CPU's which I plan to use in this machine since I can change the FSB on the AST with a jumper from 25mhz to 33mhz but I'm not sure if the voltage will be correct for the 100mhz AMD 486 which needs 3.45volts.

Does anyone know which voltage the Cyrix 486 CPU runs with? if I figure that out I know if the AMD CPU will work

IBMMuseum
May 2nd, 2008, 07:27 AM
Have recently aquired this AST machine
http://www.ari-service.com/blender/cache/501549-005.htm

It was originally fitted with a Cyrix Cx486DX2-50 CPU which I've replaced with a Intel 486DX 75mhz overdrive CPU

I have two spare AMD 486DX4 100mhz CPU's which I plan to use in this machine since I can change the FSB on the AST with a jumper from 25mhz to 33mhz but I'm not sure if the voltage will be correct for the 100mhz AMD 486 which needs 3.45volts.

Does anyone know which voltage the Cyrix 486 CPU runs with? if I figure that out I know if the AMD CPU will work

There were supposed to be some 486 Cyrix CPUs that used 4.0VDC, but I've never seen any. What voltage is your Intel 486DX4-75 (usually 5VDC, but some were 3.0VDC)? Why not try a 486 VR (voltage regulator) interposer?

rmay635703
May 5th, 2008, 04:33 PM
I had one of those I believe 2 dozen jumpers and yes it should take anything under the sun but it must be setup exactly correct or it won't post. Also the silkscreening on the board usually is wrong for some reason. Anything BELOW 5v for a non 5 volt processor is fine, you can even run that at 5v but they will run very hot and not last long. Most motherboards gave a choice of either 5v or something lower, all lower voltage chips would run OK at any of the lower voltages

As for the cyrix most all doubled chips were lower than 5v so your chip should also be of the less than 5v variety.

Good Luck


Have recently aquired this AST machine
http://www.ari-service.com/blender/cache/501549-005.htm

It was originally fitted with a Cyrix Cx486DX2-50 CPU which I've replaced with a Intel 486DX 75mhz overdrive CPU

I have two spare AMD 486DX4 100mhz CPU's which I plan to use in this machine since I can change the FSB on the AST with a jumper from 25mhz to 33mhz but I'm not sure if the voltage will be correct for the 100mhz AMD 486 which needs 3.45volts.

Does anyone know which voltage the Cyrix 486 CPU runs with? if I figure that out I know if the AMD CPU will work

vwestlife
May 6th, 2008, 02:05 PM
Does anyone know which voltage the Cyrix 486 CPU runs with?
Most likely 5.0 volts. One reason why Cyrix 486DX2 chips were briefly popular in the mid-'90s was that while Intel and AMD were switching over to low-voltage CPUs (usually 3.3V) which required either a new motherboard or an adapter to work, Cyrix stuck with the regular 5.0V voltage, which still worked with older motherboards.

Unfortunately, these chips ran hot and weren't all that stable, especially the 5.0V Cyrix 486DX2-80. Later, Cyrix released low(er)-voltage 3.45V and 4.0V versions. The voltage should be printed right on the chip itself, but some Cyrix (and Cyrix-made IBM) chips came with a permanently attached heat sink, which covered up these details.

Amigaz
May 7th, 2008, 08:25 AM
Most likely 5.0 volts. One reason why Cyrix 486DX2 chips were briefly popular in the mid-'90s was that while Intel and AMD were switching over to low-voltage CPUs (usually 3.3V) which required either a new motherboard or an adapter to work, Cyrix stuck with the regular 5.0V voltage, which still worked with older motherboards.

Unfortunately, these chips ran hot and weren't all that stable, especially the 5.0V Cyrix 486DX2-80. Later, Cyrix released low(er)-voltage 3.45V and 4.0V versions. The voltage should be printed right on the chip itself, but some Cyrix (and Cyrix-made IBM) chips came with a permanently attached heat sink, which covered up these details.

There's nothing written about the voltage on my Cyrix :sad3:

I do not dare to throw in my AMD 5x86 133mhz 3.45V cpu if I don't know the voltage...damn!

Amigaz
May 7th, 2008, 08:28 AM
I had one of those I believe 2 dozen jumpers and yes it should take anything under the sun but it must be setup exactly correct or it won't post. Also the silkscreening on the board usually is wrong for some reason. Anything BELOW 5v for a non 5 volt processor is fine, you can even run that at 5v but they will run very hot and not last long. Most motherboards gave a choice of either 5v or something lower, all lower voltage chips would run OK at any of the lower voltages

As for the cyrix most all doubled chips were lower than 5v so your chip should also be of the less than 5v variety.

Good Luck


I wish I had a voltage selector jumper on my mobo...this is the punishment when you own a desktop mass produced non AT standard motherboard :shocking:

vwestlife
May 7th, 2008, 09:13 AM
I wish I had a voltage selector jumper on my mobo...this is the punishment when you own a desktop mass produced non AT standard motherboard :shocking:
If there is no voltage selection jumper and it originally came with a DX2-50, then it is most likely 5.0V (only).