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Do 486 DX2/DX4 really need a fan?

simplex

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I've noticed on a few CPUs "Heatsink Req'd", then on seemingly identical models: "Heatsink & Fan Req'd" - whereas on others, no instruction at all.

I've barely ever seen fans on 486-class processors... is there really any point in 100Mhz + less?
 

griffk

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I've noticed on a few CPUs "Heatsink Req'd", then on seemingly identical models: "Heatsink & Fan Req'd" - whereas on others, no instruction at all.

I've barely ever seen fans on 486-class processors... is there really any point in 100Mhz + less?


I think you can only answer that on an individual basis. Some MBds had sockets that provided more "natural" heat dissipation

And the environment (case, PS, drives, HS grease, Size&material of HS, etc.) that the uP's were installed in, make a lot of difference. There were definitely fan/HS combos being used on 486 processors, and the best way to determine if you can get away without one, is to let an assembly "cook" for 10 minutes, under power, and aim a good IR thermometer at the uPs edge (or as close to the core as you can get).

gwk
 

vwestlife

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I had a 5-volt Cyrix 486DX2-80 that only had a heatsink on it. That's the fastest 5-volt CPU I've seen that did not have (or need) a fan.
 

krebizfan

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Heatsink is basically required for any DX2/DX4. Fortunately, many of the 5v models were packaged with a tiny heatsink which suffices. Fan on the CPU can often be skipped if there is good airflow in the rest of the case. Tradeoff: big loud power supply fan or whiny little CPU fan. Having a CPU fan will never hurt the system, so even if it is not required, installing a CPU fan is often a good idea.

The very fast higher voltage AMD models should get a fan if possible because they are running right up to the heat limits of the chip. You can get away without the fan for some time but the CPU will fail a lot sooner than normal.

Overclock: get a fan
Run 24/7: get a fan
Got a spare buck: get a fan
 

vwestlife

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Cyrix did make a 486DX4-100 that didn't need a fan:

Cyrix_Cx486DX4-100GP_pinkie.jpg


And many 486-to-5x86 CPU upgrade modules used the laptop version of the AMD 5x86-133 chip, which also only needed a heatsink:

81ufx-ftYCL._SY355_.jpg
 

Unknown_K

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I have a couple Planar 486 systems (medical use) that have CPUs (100mhz Ti I think) without a heatsink or fan (ceramic processors) but ad a fan blowing on them.
 

Chuck(G)

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Heat is the enemy of all electronics. Any bit of kit that will run with no fan installed will last longer with a fan--or some other type of cooling. That's not to say that a fan mounted on a heatsink is the best solution. I'd much rather see ducting from the heatsink to a generous PSU fan be used. Small fans just don't move much air and use the heated air from the inside of the enclosure to cool. Better to take in outside cool air to do the job.
 

Scali

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I've noticed on a few CPUs "Heatsink Req'd", then on seemingly identical models: "Heatsink & Fan Req'd" - whereas on others, no instruction at all.

I've barely ever seen fans on 486-class processors... is there really any point in 100Mhz + less?


It depends.
I had an AMD 486DX2-66, which required a heatsink+fan. It died after 2 years of use, presumably because the fan broke down. I replaced it with an Intel 486DX2-66 overdrive, which only had a heatsink glued on from the factory, no fan required.
Another Intel 486DX2-66 was in a Compaq Deskpro, which had a third-party heatsink put on (considerably larger than the one Intel put on the overdrive), and the case was designed so that the case fan generated airflow over that heatsink. The fan was probably overkill for the 486DX2-66 though, but the same case was also used for other machines. I have one with a Pentium Pro 200.

It could have to do with binning, perhaps they sorted them on fan-required and fan-less, depending on the needs for system builders (eg, I bet the overdrive CPUs were carefully selected, because they were sold as an upgrade for 486DX-machines, so they had to work inside systems that were not designed for anything more than a regular DX in terms of power draw and heat dissipation).
Another issue could be that later models used more mature manufacturing, so the chips ran less hot, and the fan may no longer have been required.
There have been some die-shrinks, and later 486 CPUs ran on 3.3v instead of 5v, so that also has an effect.
I guess you'd have to pay close attention to the details of the CPU, eg the build date and/or the serial number. They may explain why one DX2/DX4 is not the same as another DX2/DX4.
 
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SpidersWeb

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I pulled a dead AMD 486DX2/66 out of a motherboard last weekend. "Heatsink and Fan Req'd" but no signs of one ever being used.
Probably ran for years just fine like that, but it certainly seems to have suffered a short life compared to it's brothers.

I have some which don't have the message and seem to have lasted fine without one, but I'm tempted to install heatsink/fans anyway as it doesn't take long for them to get hot either and I'm sure it's not doing them any favours.
 

Uniballer

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Adequate cooling is a must, but I would suspect that reliability is also affected by leaving the system running 24/7 (and not sleeping) rather than turning it on and off frequently. I would expect heating and cooling cycles to increase stresses in a lot of areas (e.g. bonding wires inside chips, hard disk parts, etc). Is there any real (i.e. non-anecdotal) evidence on this?
 
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griffk

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I pulled a dead AMD 486DX2/66 out of a motherboard last weekend. "Heatsink and Fan Req'd" but no signs of one ever being used.
Probably ran for years just fine like that, but it certainly seems to have suffered a short life compared to it's brothers.

I have some which don't have the message and seem to have lasted fine without one, but I'm tempted to install heatsink/fans anyway as it doesn't take long for them to get hot either and I'm sure it's not doing them any favours.

I think you are on the right track-ANY install will benefit from a CPU fan. Many say they dislike the extra noise, but many CPU fans these days have almost zero dB, so that shouldn't be a show stopper.

The extra headroom provided by active cooling can increase the CPU's lifespan a great deal. And the extra $ can be eaten up real fast, if you end up having to do a CPU replacement because of heat death...

People buy frivolous insurance all the time--In this case, it's NOT frivolous, and yet many tempt fate?? Go figure!

gwk
 

GiGaBiTe

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And many 486-to-5x86 CPU upgrade modules used the laptop version of the AMD 5x86-133 chip, which also only needed a heatsink:

81ufx-ftYCL._SY355_.jpg

Even though that Evergreen AM5x86-133 didn't have a fan, it required one if you ran it at 80+ MHz. That's why there's a fan header on it.

I had one of them and made the mistake of trusting the tiny heatsink and it suffered thermal death after about 2 years.
 

griffk

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Adequate cooling is a must, but I would suspect that reliability is also affected by leaving the system running 24/7 (and not sleeping) rather than turning it on and off frequently. I would expect heating and cooling cycles to increase stresses in a lot of areas (e.g. bonding wires inside chips, hard disk parts, etc). Is there any real (i.e. non-anecdotal) evidence on this?

I refer you to the story running now on the 30yr old AMIGA 2000 that's controlling HVAC in a school district somewhere in the Midwest - That thing probably hasn't been turned off in all of those 30 years (except for maintenance, cleaning, etc.), and it's still chugging along...

When PCs first hit the market, this was a BIG philosophical argument - Leave On Vs Power Off When Unused - and the argument continues to this day!

Not only for PCs, but for ALL electronics (TVs specially). As an engineer, I always leave electronics ON, as much as possible. If you look at current inrush/spiking on an oscilloscope, you will be a lifelong believer in MOVs, and the power of that ON-OFF cycling to do real damage to circuits...

gwk
 

GiGaBiTe

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They could have used a larger heatsink.

On the Evergreen chip? Not easily.

The heatsink would have to be a very unusual design because the fan header, capacitor, power transistor and the jumpers would get covered up. You could make it taller, but it'd limit what systems it could be used in. Many desktop machines were cramped and sometimes had a drive or PCB right above them.
 

griffk

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On the Evergreen chip? Not easily.

The heatsink would have to be a very unusual design because the fan header, capacitor, power transistor and the jumpers would get covered up. You could make it taller, but it'd limit what systems it could be used in. Many desktop machines were cramped and sometimes had a drive or PCB right above them.

They were getting enough $$ for that chip/bd, that they could have INCLUDED some active cooling (thin-style fan or heat pipe or ??)...

gwk
 

vwestlife

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I'm sure the Evergreen module uses the ADZ version of the AMD 5x86, which has the highest temperature rating. (The ADZ was supposed to be sold as a 160 MHz chip, but AMD feared it would cut into K5/K6 sales too much, so they sold it as a "133 MHz" chip.)
 

paul

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..As an engineer, I always leave electronics ON, as much as possible. If you look at current inrush/spiking on an oscilloscope, you will be a lifelong believer in MOVs, and the power of that ON-OFF cycling to do real damage to circuits...

25 yrs ago in my mechanical engineering group of 12, I had half turn their clone '486s off at night and the other half leave them on. Not that it's statistically convincing, but the only conclusion I could draw after about 5 years is that more fans failed to start properly in the group of PCs turned off at night, but that's a pretty common fault with cheap fans anyway. Otherwise the PCs became obsolete long before any other failure, including hard disks.

Frankly, I don't think PC electronics suffers from a nightly shutdown as even 365 cycles a year is still very small for thermal cycling stress. And if it can't take the electrical transients, it hasn't been designed correctly. My only exception would be PCs with older hard disks that have the brown oxide coating.
 
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