Ideas on how to cool an 80486 - Page 1
Forum section: electronics / general

author: Ampera
author_rank: Super Contributor
timestamp: November 02, 2016, 04:20:32 pm
content: So I am currently making a retro gaming build (Sorry for actual 80486 users for the term "retro") based around the 80486(AM486)DX4-100 chip, which gets hot. How hot does it get? I have no clue,and can't find a source. The board (EDIT: the chip comes with the board) I plan to buy appears to have been clocked at 120Mhz (How I don't know) so I imagine it will run even hotter.Normally a small heat sink would be applied, my guess with a thermal glue, but I don't want to glue it down in order to preserve the look of the CPU. My question is if I can't just get like a small sideways blowing laptop type fan, and blow it directly on the un-heatspreaded chip, and what sort of static pressure/airflow would be nice? I can't imagine them getting all that hot, since just a DX2-66 doesn't need anything.Thanks for any suggestions, the 80486 line is a bit before my time (born 2002) so aside from an IBM PS/1 that had some sort of 80486, I have never owned one.

author: bktemp
author_rank: Super Contributor
timestamp: November 02, 2016, 04:37:44 pm
content: Quote from: TwoOfFive on November 02, 2016, 04:20:32 pmMy first PC was a DX2-66 and it needed a heatsink (but without a fan). DX4-100 typically had a small heatsink + fan.

author: helius
author_rank: Super Contributor
timestamp: November 02, 2016, 05:20:28 pm
content: These chips usually have "HEATSINK AND FAN REQD" printed on them, as they were some of the first x86 processors to require them. Without a heatsink, the thermal conductivity is too low to shed the TDP of around 5-6 W.

author: SeanB
author_rank: Super Contributor
timestamp: November 02, 2016, 05:28:27 pm
content: There should be a set of holes around the processor socket, to attach the standard heatsink and fan combo they needed. Otherwise use a larger Intel heatsink, and use the holes to attach it to the heatsink with cable ties. Bodge, but works well enough, and you just use normal thermal compound.Otherwise use a bit of thermal epoxy and the common Intel round heatsink and you will not even need the fan.

author: Ampera
author_rank: Super Contributor
timestamp: November 02, 2016, 05:29:04 pm
content: Quote from: helius on November 02, 2016, 05:20:28 pmI just wonder if I can't just have a decent fan on it and that will do it, for as I said I don't want to glue a heatsink on it.

author: senso
author_rank: Frequent Contributor
timestamp: November 02, 2016, 05:30:34 pm
content: If you dont mount an heatsink you ruin the silicon, get a dead one from ebay and frame it, and put a real heatsink in the one you plan to use..

author: Ampera
author_rank: Super Contributor
timestamp: November 02, 2016, 05:31:32 pm
content: Quote from: SeanB on November 02, 2016, 05:28:27 pmThe issue here is that this is not your standard motherboard. They did not have heatsink mounting for socket 3 that I know of, and my board certainly doesn't. I thought about using a spare AMD or Intel heatsink if I still had one and just cutting it down, but that just requires me to glue it on since there is no way to mount it. I would have to glue it on, so I want to know if I can't just position a strong fan near the chip without any heat spreader attached.

author: Ampera
author_rank: Super Contributor
timestamp: November 02, 2016, 05:34:20 pm
content: Quote from: senso on November 02, 2016, 05:30:34 pmI want to know if I can just mount a strong fan and if the air thermal interchange rate of the ceramic will be enough for me to mount this.I need to say this again, 80486 CPUs rarely needed cooling, but the more powerful DX4s definately did, especially when clocked at 120Mhz. There is no mounting screws, and no mounting hardware, a heatsink mount would require a thermal glue that will never come off. The idea of framing one from Ebay is interesting, but not the idea I had in mind, I would rather have no heatsink and just a good fan if I could get away with it. If the answer is a definite and total no, I will get the thermal paste.

author: helius
author_rank: Super Contributor
timestamp: November 02, 2016, 05:43:02 pm
content: Also pay attention to whether your processor is 5V or 3.3V; the latter will fit into a 5V socket but won't work as intendededit: typically the way heatsinks were mounted to 486s was with plastic side clips. At 6W TDP, you don't need strong pressure or super-thin thermal paste. Use generic silicone putty and affix with normal hand pressure.

author: Kilrah
author_rank: Unknown
timestamp: November 02, 2016, 05:57:16 pm
content: My memories from that era (that may or may not be very accurate) are that later MoBos that were designed for these higher TDP chips had clips on the Socket 3 to attach a heatsink with a bracket.

author: Ampera
author_rank: Super Contributor
timestamp: November 02, 2016, 06:05:57 pm
content: Quote from: helius on November 02, 2016, 05:43:02 pmAlright, Socket 3 does both 5v and 3.3v, and I do think that mine has clips (sorta two small square holes in the back of the ZIF socket?)I still want to know if anybody thinks I can't just blow a good fan over it, in that event I don't need to buy anything.

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 02, 2016, 07:23:03 pm
content: Quote from: SeanB on November 02, 2016, 05:28:27 pmErr, no. They only started fitting those when the heatsinks became too heavy to have them glued directly to the ptocessor.

author: Halcyon
author_rank: Unknown
timestamp: November 02, 2016, 07:26:30 pm
content: Quote from: TwoOfFive on November 02, 2016, 04:20:32 pmWelcome to the club! There are plenty of retro-computing aficionados here.Quote from: TwoOfFive on November 02, 2016, 04:20:32 pmI have a 486 DX-2 66MHz at home which still gets quite hot. Even though they were commonly run without a heat sink and/or fan, I threw one on anyway. After all, cooler is better. From memory the socket on my board has the little clips which held the heat sink in-place via a metal retaining clip. In your case, you'll need to get hold of something like the one in the image below. The heat sink is held in-place with little clips that grip the CPU itself. These were very common in 486 machines back in the day. You'll also need some thermal grease or pad to go with it. It doesn't need to be anything special -- I use Dow Corning 340 compound for most applications (although in my 486 I used the old Beryllium Oxide compound as I still had a tube left). That way, you don't need to worry about ruining the original finish or look of the processor, the grease cleans off relatively easily.Quote from: TwoOfFive on November 02, 2016, 05:34:20 pmThere is no point. A fan and no heat sink won't do anything. You'd better off with just a heat sink and no fan.EDIT:Your other option is to run the CPU at a lower speed by changing the jumper settings (essentially "under clocking"). So instead of 100 MHz, run it at 80 MHz. Or if your machine has a turbo switch, just turn that off. That'll reduce the heat output. 100 MHz was fast for a 486 anyway, the machine I have runs at 33/66 MHz (in non-turbo and turbo modes).

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 02, 2016, 07:26:51 pm
content: I remember clip-on heatsink and fan, like this:I don't think you can get away with a fan blowing at the cpu alone.Edit: Yes, Halcyon was just ahead of me...Edit 2: I'm sure I still have one, but where...?

author: CJay
author_rank: Super Contributor
timestamp: November 02, 2016, 08:17:10 pm
content: Quote from: TwoOfFive on November 02, 2016, 05:31:32 pmThey most certainly did have heatsink mounting on socket 3, at least they did if it's a ZIF socket, along two opposite edges you will find two 'wedges' which protrude out and have a notch on the underside, they're for fixing a spring clip to hold a heatsink.

author: Halcyon
author_rank: Unknown
timestamp: November 02, 2016, 08:25:11 pm
content: Quote from: CJay on November 02, 2016, 08:17:10 pmSome did (my board does) but many didn't. It wasn't uncommon at all to have a ZIF socket without the heat sink retention tabs. They became more common in the later boards.

author: CJay
author_rank: Super Contributor
timestamp: November 02, 2016, 08:30:14 pm
content: I stand corrected then, I don't remember seeing any without but it was a long time ago.There are lots of ways to attach the heatsink, including the under chip clips though.Memory lane

author: Halcyon
author_rank: Unknown
timestamp: November 02, 2016, 08:34:56 pm
content: Quote from: CJay on November 02, 2016, 08:30:14 pmHeh, just one of those things. We take them for granted now.

author: Ampera
author_rank: Super Contributor
timestamp: November 02, 2016, 09:09:35 pm
content: Quote from: Halcyon on November 02, 2016, 08:34:56 pmAlright. Thanks for the information, I will try a fan to see if it will do something as my hunch is that since it doesn't get THAT hot that quickly, a fan might be enough. In the event it doesn't and my chip gets too toasty, I will try something else. My impression is I won't fry the chip instantly running without cooling, but that it would be a lot better if I had something.

author: Halcyon
author_rank: Unknown
timestamp: November 02, 2016, 09:20:03 pm
content: Let us know how you go.You're unlikely to fry it anyway, it'll just overheat and probably start locking up. Those CPUs were pretty robust. They weren't known to catch fire like the AMD CPUs ;-)

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 02, 2016, 09:31:49 pm
content: Quote from: Halcyon on November 02, 2016, 09:20:03 pmEven the AMD ones of that generation weren't IIRC. That was the claim to fame for the K6, wasn't it?

author: Kilrah
author_rank: Unknown
timestamp: November 02, 2016, 09:35:53 pm
content: Quote from: Halcyon on November 02, 2016, 09:20:03 pmBut it IS an AMD CPU he's using!But yeah, was mostly later models that had the issue. Not sure about the 486s...

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 02, 2016, 09:47:04 pm
content: Quote from: Kilrah on November 02, 2016, 09:35:53 pmI might be recalling things wrong but as far as I remember the issue only came to be after you started needing different boards for Intel and AMD CPUs while at 486 times both still ran on the same boards.

author: Ampera
author_rank: Super Contributor
timestamp: November 02, 2016, 11:13:01 pm
content: Quote from: NottheDan on November 02, 2016, 09:47:04 pmYea this is a Socket 3 board, I'll give the page of where I bought it (didn't want to before in case someone else swiped it)http://www.ebay.com/itm/252522204439It actually seems to be a pretty decent board. From what I can tell it has 256k of cache, and I plan to upgrade the 32MB provided with top of the spec 128MB of memory.If you want the rest of the parts there are as follows, keeping in mind this is what I was able to find, not what I should have got.As a side note I am perfectly aware of the issues with VLB, I wanted to use it anyways as struggling with stupid old hardware is half the joy of retro computing, and wouldn'tbe complete without it.For the video card I went with the Diamond Stealth SE VLB, upgraded to 2MB of FPM-DRAM. Not the mostpowerful options, A Mach 64 or Speedstar Pro would probably have been the dream card, but I couldn't find one for a decent price.The rest of these specs are pretty OP for an old 486, but if I am gonna build a 486, I might as well go all out and build the best one I can.For the CPU, I went with the previously mentioned AM486-DX4-100, one of the best 80486 chips, and it's even clocked to 120Mhz by the seller.For memory I said I did 128MB, an amount I will probably NEVER need, but I sprung for it anyways thinking 20 bucks with free shipping was too cheap to pass up.The MultiI/O controller I have is a DTC2278D, with two IDE channels for up to 4 drives, and it appears to have every interface known to 1993 man.The hard disks are actually ones I already have, they are Western Digital Caviars, each about 2GB that I plan to have on a swap out arrangement with Windows 3.1, NT 3.1, and OS/2 (whatever version I find) on one of each. I could do an early multi-boot but I want to keep to single disk environments for nowThe sound card is pretty beefy as well, an AWE64 which is a Sound Blaster 16 + MIDI (Slightly better MIDI than an AWE32, but no memory upgrade abilities)I also have some AT bugger off power supply off Newegg (Who knew they still made and sold them, it's just a standard that already exists and can be powered on without needing to short the power connector)and a dual 5.25 and 3.5 inch combo drive I plan to slap in and a random IDE CD drive I have laying around (would rather have one that works than deal with the ultimate joy of something like a Sony controller)Thanks for all the help, I will make sure to get a decent fan on the chip, and I can always pick up a heatsink if it doesn't work out.That about covers everything, the mobo comes from Russia, so if it survives WW3 (bad joke), it should be here in about a month, but the rest will trickle in.

author: Red Squirrel
author_rank: Super Contributor
timestamp: November 02, 2016, 11:32:06 pm
content: I remember playing around with my sister's university computer, was the first computer I ever used, and eventually, opened. It had a 486DX2 running at 66Mhz (or 16 if turbo button is off, those were cool!). It had a small heat sink and fan, but it was just physically attached, no adhesive or thermal paste. I guess for how hot the cpu got, simple mechanical contact was good enough.So you may be able to get away with something like this, maybe using foil paper as something a bit "squishy" for it to press against. Assuming it's a ceramic package like the DX2 was. Proper way would be to use thermal paste though. I would not use any kind of glue, you still want to be able to remove the heat sink.

author: Ampera
author_rank: Super Contributor
timestamp: November 02, 2016, 11:52:59 pm
content: Quote from: Red Squirrel on November 02, 2016, 11:32:06 pmNo, I am using a good fan to just blow air over the ceramic. It will never be anywhere near as good as a heatsink, but it will preserve the look which is what I'm after.

author: Halcyon
author_rank: Unknown
timestamp: November 03, 2016, 12:23:57 am
content: Quote from: Kilrah on November 02, 2016, 09:35:53 pmAhhh! We're all gonna die!!Yes you are right, it started around the time of the K6's and continued on to much newer CPU's. As you can tell, I'm generally not a big fan of AMD. Too flaky for my liking.You might be better off just buying a new CPU instead of spending money on fans and heat sinks. Something like the 486 Overdrive series of CPU which had a heat sink built-in. You could even attach a little fan if you wanted by fixing the screws in between the fins.http://www.ebay.com.au/itm/Vintage-CPU-INTEL-486-486-DX2-486DX2-DX2-66-Overdrive-CPU-/302121593647

author: AlxDroidDev
author_rank: Frequent Contributor
timestamp: November 03, 2016, 01:36:53 am
content: The 486s from AMD had no overheating protection. If they got too hot they'd just fry. If you run an overclocked AMD 486 without any heat sink + fan, you'll fry it in seconds.The overclock on most of these boards is done using jumpers that increase either the bus speed, it's multiplier or both.

author: sleemanj
author_rank: Super Contributor
timestamp: November 03, 2016, 01:49:24 am
content: I am pretty sure that this was off a DX4/100, repurposed a couple years back. The slot n the middle was for a metal clip as previously described. No fan.And this is a P75 and it's heatsink out of my junk bin.

author: Ampera
author_rank: Super Contributor
timestamp: November 03, 2016, 02:05:37 am
content: I think I am just gonna grab a heatsink, I might have some Arctic Silver left, if not I also have some spare grease from an old enermax air cooler.

author: CJay
author_rank: Super Contributor
timestamp: November 03, 2016, 08:04:11 am
content: Good plan but there are places that sell 'proper' 486 heatsinks still.And as you've got the AMD variant, try to source a real Intel chip instead, it'll whup the AMD's performance, the AMD on board cache was woeful, IIRC they benchmarked at around half the Intel chips level because of it.

author: Ampera
author_rank: Super Contributor
timestamp: November 03, 2016, 07:55:17 pm
content: Quote from: CJay on November 03, 2016, 08:04:11 amThis is not true in my case. My AM486 chip will actually bench higher or equal to an i486 (DX4-100) since I bought the Write-Back16Kmodel that has the improved cache over the older versions. Swapping out for an Intel chip will only hurt me money and performance wise. And your statement of "Half" is not accurate in the slightest.EDIT: It is a SV8B, meaning Write Back, but only 8K. It's still not going to be hurting much since it's possible this is what they meant by WB in the benchmarking.And honestly this is the chip I have and I'm perfectly fine with it, if I am in the process of swapping out chips for something better I would grab a DX4-120 instead of a 100. And the chip came with the board which cut down on cost for me.http://www.vogons.org/viewtopic.php?t=28470This old Vogons post shows the almost equal performance (When compared to a Pentium 100) of the I486DX4-100 and the AM486DX4-100 WB, with the WT model scoring only slightly lower at the level of Cryix's chips (Designed to be budget performers). Not only that, but this is only compared to a Pentium 100, and doesn't fully show the actual tick for tick performance of the AMD vs Intel's versions, and only gives a rough comparison to the Pentium 100, but nowhere here is it ever half the performance.This makes sense too, how would half the performance (Effectively a DX2-50 or so) make sense to anybody? Especially as this was already after the DX4-75, DX2-66 etc. It clocked slightly lower, but only slightly.But even so, thanks for making me check my stuff, this is my first time with building anything older than ATX, so I am not the best at this.

author: Ampera
author_rank: Super Contributor
timestamp: November 07, 2016, 04:40:23 pm
content: This is interesting (Sorry for bumping a sorta dead post, but I found this)http://ipic.su/img/img7/fs/DSC_0054.1472798129.jpgThis is a picture off the ebay listing for the motherboard/CPU combo I bought.It says on the bottom right corner "16KB of L1 Cache"But on this picture (Same listing)http://ipic.su/img/img7/fs/DSC_0230.1472798114.jpgYou can see the model of the CPU is SV8B.https://en.wikichip.org/wiki/amd/am486/am486dx4-100sv8bThis site claims it has 8KB of WB cache, and that I don't get.Either the program is thinking it's an Intel 80486-DX4-100, or the chip is marked wrong?I want to be it's the program, but who knows, if anybody has a definite test for this chip to test the L1 cache, let me know and I will run it.

author: CJay
author_rank: Super Contributor
timestamp: November 07, 2016, 06:39:59 pm
content: Quote from: TwoOfFive on November 03, 2016, 07:55:17 pmYup, I was rather confused when I read your reply but it's my dodgy memory, it was the DX2 chips that scored roughly 144 and 72 on Norton SI respectively (which is really an odd coincidence but I believe it was related to cache)I went back and had a look through some old stuff I wrote way back when (usenet) and realised you're right.

author: Halcyon
author_rank: Unknown
timestamp: November 08, 2016, 12:35:46 am
content: Yeah not sure what's going on there. It looks like you may have a misprinted CPU.The A80486DX4-100SV8B definitely only came with 8KB of L1 cache, however the inscription on the bottom-left (25544) doesn't seem to match that CPU. Having a look atcpu-collection.de, that inscription matches the Am486DX4-100V16BGC and the AMD Am486DX4-100SV16BGI which both came with 16KB of L1 cache. I don't know what the 5-digit inscription corresponds to though (some websites refer to this code as the "AMD Package Number").AmiDiag is my go-to application for testing hardware on older machines. If that says the 16KB of L1 cache checks out, then I'd believe it. Let me know via PM if you want me to e-mail you a copy.The only other conclusion I can draw from this is if was a fake CPU? If you aren't getting the performance out of it as you'd expect, maybe it is? I have no idea if that was "a thing" back in those days. Admittedly if it was a fake, I'd be very surprised as it looks very much genuine. Although the colour of the ceramic looks different.EDIT: I just did a quick Google and there did seem to be a few fake Intel and AMD CPU's getting around back in the day (even as early as the 286).One guymentions that he has a fake A80486DX4-100NV8T in his collection.This sitelists a fake AMD P90. Finally,this guyalso has a A80486DX4-100SV8B in his collection but the font and some of the text looks different to the one you have (curiously it still has that 25544 number on it). What can I conclude from all of this? Not much. At the end of the day, if the CPU you have performs like an AMD 486DX4-100, the cache checks out OK and it's relatively stable (although it is an AMD after-all) then I'd say you've probably got a genuine misprinted CPU.

author: Ampera
author_rank: Super Contributor
timestamp: November 08, 2016, 03:15:22 am
content: Quote from: Halcyon on November 08, 2016, 12:35:46 amI don't currently have the CPU at the moment, but I will pm and run that test when I get it set up. It IS from Russia, so you never know, but it would be GREAT if I suddenly have a 16k model