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Topic Title: Solving FSB Problems (Athlon XPs)
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Created On: 06/09/2004 11:33 PM
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 06/09/2004 11:33 PM
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So your Athlon XP system won't run at the FSB it's supposed to. A whole lot of things could cause this, which is why this guide is so long. It's probably best to go through these in order, and, uh, please don't skip a step, because they're all fairly important. Without further ado...

1. Are you sure you're trying to run the processor at the correct FSB?

Don't snicker. This happens, and often. If you have an Athlon XP 2600+ or 3000+, you should really worry; if not, make sure anyway. The correct FSB for any Athlon XP up to 2400+ is 133MHz (266MHz effective), the correct FSB for the 2500+, 2700+, and 2800+ is 166MHz (333MHz effective), the correct FSB for the 3200+ is 200MHz. Remember that unless your only options are 200MHz and up (ex. 200MHz / 266MHz / 333MHz), you should always enter the real FSB speed (ex. 133MHz instead of 266MHz).

Now, what was I saying about the 2600+ or 3000+? Well, they come in different flavors in a way that is very very important. If you don't mind taking a look at the processor itself, take a look at the OPN. The OPN, if you don't know, is on the first line of the black sticker on the processor, and it will tell you all the basic specifications that you need to know. Take a look at the last character (In, for example, AXDA3000DKV4E, it's the "E"). If it's C, the FSB is 133MHz (266MHz effective). If it's D, the FSB is 166MHz (333MHz effective). If it's E, the FSB is 200MHz (400MHz effective).

Don't want to take the heatsink off? In that case, set the FSB to 100MHz and see what speed it boots up at. Motherboards almost always get the MULTIPLIER right, so that should do the trick. FOR 2600+: If it boots up at 1150MHz, you've got a Barton, which means the FSB should be set to 166MHz. If it boots up at 1250MHz, you've got a later Thoroughbred-B with an FSB of 166MHz. If it boots up at 1600MHz, you've got a semi-rare early Thoroughbred-B with a 133MHz FSB. FOR 3000+: If it boots up at 1050MHz, it's the later version with a 200MHz FSB. If it boots up at 1300MHz, it's the earlier version with a 166MHz FSB.

2. Is your motherboard the problem?

Make sure that your motherboard can in fact support the FSB that you want to run it at. Remember, if you have a 2600+ or 3000+, just because your CPU's on the supported CPUs list for that board doesn't necessarily mean your board will take it; some boards only go up to a 133MHz FSB and won't take FSB166 2600+es, some only go up to a 166MHz FSB and won't take FSB200 3000+es.

There are also timing issues on certain motherboards. Set the FSB a couple MHz below or above the correct setting and see if that fixes it. These only occur with a few boards, but they do happen.

Also, voltage fluctuations or lower-than-normal voltages can cause instability and/or damage. Go into whatever section of your BIOS monitors voltages (often it's called the Hardware Monitor) and check Vcore (AKA CPU voltage AKA core voltage). For old Palomino Athlon XPs, it should be 1.75v. For low-speed Thoroughbred-As like the 1700+ through 1900+, it should be 1.5v. For low-speed Thoroughbred-Bs like the 1700+ through 2100+, it should be 1.6v but MIGHT be 1.5v for the 1700+ and and 1800+. For anything else, it should be 1.65v. If it's varying wildly, you've definitely got a problem, but first make sure it isn't a PSU issue. If the +12V, +5V, and/or +3.3V rails are also fluctuating wildly, odds are it's the PSU; if not, something's wrong with the motherboard's voltage regulators.

3. Is your memory the problem?

First off, does your memory match or exceed the processor's FSB speed? For an FSB133 processor, that means you need PC2100/DDR266 or faster memory; for an FSB166 processor, you need PC2700/DDR333 or faster memory; for an FSB200 processor, you need PC3200/DDR400 or faster memory.

Next, just because it matches the processor's FSB doesn't necessarily mean it's going to run right at that speed without issues. The first thing to do is run Memtest86' "> Don't worry, running it isn't really a pain, just run the setup program to install it to a floppy and boot from it. If you don't have a floppy drive, they have a bootable ISO on their site.

If it does all seven default tests without reporting any problems, you're fine. If it says there's a problem, there is a problem (surprise!. Set the memory timings to SPD or Optimal in the BIOS and run it again. If it still reports a problem, bump the memory voltage to 2.7 volts. If you can't bump the memory voltage (most boards WILL allow you to do this, just look around) or that doesn't help, set the memory timings to manual and set CAS Latency to 3.0, set Row Active Time (tRAS) to 8T, and set Row Precharge Time and Row Address to Column Address Delay (tRP and tRCD, respectively) to 4T. If it still reports problems, return your memory for a new stick; getting a different brand would probably be best in case there are compatibility issues with your board. Branded (Corsair, Mushkin, Crucial, Kingston) is the best way to go.

4. Is your CPU running too hot?

First, turn your computer off and leave it off for a while. Then turn it on, rush into the BIOS, and record the temperature as soon as you can. If it's significantly above room temperature, you can safely assume that it's overestimating the temperature of the CPU by roughly whatever the difference between that temperature and room temperature is minus two or three degrees. Now Sit around in the BIOS for a while looking at the temperature. If it goes up above fifty-five degrees Celsius or so (55C after accounting for any overestimation, that is), heat could well be the problem. If it isn't, don't worry about heat, just head to #5.

Now, touch the heatsink and see if it's hot at all. If it is, take a big desk fan and aim it straight at the heatsink, then try and boot at the right FSB. If it's stable then, either you need a new CPU fan or you need some new case cooling. How are you supposed to know which? Uh.. if you already have even one exhaust fan sitting in the case (at the back, that's where the exhaust fan should go if there's just one), you're probably fine. Just measure the length of one side of the current fan on the heatsink to find what size you need, then get a reasonably good fan of the right size (probably 80mm, could be 60mm though). Might as well go quality and get a Panaflo or something, fans are cheap. Don't get one that's too loud or you'll regret it; for Panaflos, an "M" series fan (medium-output) would do fine.

What if it isn't hot at all? Uh, then you have a thermal contact problem. First, make sure the heatsink is on right. That... guh, I can never find a good way to say this. Okay, you know how one end of the base of the heatsink has a bar where the base is above the rest of the heatsink? That's the side that should be on the top of the socket, the part of the socket that's raised above the rest. In this image here' ">, it's on the right.

If it's on right, what's between the heatsink and the processor? If it's just a pad or some pre-applied gunk, you might have to take it off and apply some thermal compound like Arctic Silver Ceramique. If it's a pad/gunk AND goop, that's bad, and you should take one of them off. If you applied some compound yourself and there's nothing else on the base of the heatsink, how much did you apply? The thinner the layer, the better; thermal compound is terrible at conducting heat, the only reason we use it is because it sure beats air. If you applied a lot, clean it off and put a very thin layer on the core. If that still doesn't solve it and you were using cheap compound, get a small tube of Arctic Silver Ceramique and apply a thin layer of that.

5. Is your power supply the problem?

There's a pretty easy way to test your PSU's output. Take out anything you don't need to make it into your OS stable. Optical drives (that means CD/DVD drives), probably most of your PCI cards, any hard drives that don't have your OS. If it's stable at the right FSB, you need a new power supply. Go for a good brand name like Enermax or Antec. If it isn't, just check all the rails to make sure the PSU can handle the system. You'll want at least 28A on the +3.3V rail, 28A on the +5V rail, and 15A on the +12V rail. If your PSU doesn't offer that, you should get a new one... after exhausting all other possibilities, of course. Some systems will run with a slightly weaker +3.3V or +5V rail, and why spend money on something that you're not totally sure is causing the problem? (If you're under 24A on either of those first two rails, you've really got a problem, and in my opinion you should just replace it.)

Output isn't everything, though... exactly what real voltage your PSU is putting out also counts, though it's unlikely to be the cause of this problem. If you have a multimeter, test the actual voltage of the +12V, +5V, and +3.3V rails; you can test +12V and +5V with a molex plug (+12V is the yellow wire, +5V is the red wire), but unfortunately I don't know where to test +3.3V except for the ATX plug. Why's that a problem? Uh, if that's not plugged in the PSU won't want to turn on, so you'll have to short the POWER ON wire (green) by connecting it to a ground wire (black, of course). The +3.3V wire is orange.

If you have no multimeter, don't worry about anything I just said. Go into the BIOS and check what voltages your motherboard says the PSU's putting out. (In case you're wondering, I suggested the multimeter first because the BIOS isn't all that accurate for voltage monitoring, and a good multimeter would be better for testing.) No matter what you used to test it, if the voltages are too far off (I wouldn't want to see anything more than 5% off, myself), yup, you should probably get a new PSU.

In all cases, testing it with a "known good" PSU is preferable to getting a new one right off the bat, just so you can make absolutely sure.

6. Is something wrong with the L2 cache on your CPU?

It'd be really weird if the L2 cache only worked at a lower speed, but it could happen, and there's certainly no harm in giving this a try. (It doesn't cost anything and there's no risk, which means it's worth it, heh.) Disable the L2 cache in your BIOS and see if it's stable at the right FSB then. If it is, you've got a defective CPU and you should return it.

If none of this helped, congratulations, you have a special problem. Hopefully someone in the troubleshooting section will be able to help.

DEC Pentium X2 5200+ w/ HyperCache (Ezra core)
Asus M7NCD-MAX3 (OPTi Vendetta 82C760)
6x Generic 32MB PC2700 RDRAM (50ns SIMMs)
2x nVidia Millennium X1800 Duo (SLI mode)
12x (daisy-chained) Quantum Medalist 180GXP (w/ separate SCSI-1 adapter)

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