Fact:
All 2200+'s and higher come with the cpu multipliers unlocked (L1 bridges closed)
Fiction:
Closing L3-5 bridge unlocks the cpu.
Fact:
L3-5 is actually the 8x multiplier bit and closing it changes your default cpu speed.
Fact:
Most boards prior to about Oct. 2002, didn't support all five multiplier bits that have been there since the XP product line was introduced.
Fiction:
Anything that states something other than closed L1 bridges unlocks the cpu.

And now for the story.

Contrary to the title of this, the problem actually started with the introduction of the Athlon 2100+ XP (Palimino core) cpu. It was the first XP that actually made use of a multiplier higher than 12.5. It's default multiplier is 13. To get to this speed the 5th multiplier bit had to be set high and it was done.  Most people with 2100+ cpu's never realized there was a problem with their board for one simple reason. The cpu was shipped locked, meaning all L1 bridges were cut in the factory so the board would run at default multiplier settings on all boards. The problem arose when people started to connect the 5 L1 bridges so they could set the multiplier via jumpers, bios, or whatever means their board provided. But now some boards wouldn't boot using this cpu. The reason is a simple one. Most (if not all) board manufacturers never implimented the 5th bit of the multiplier set of 5 bits. So the blame for this problem, if one is to be put on anyone, should be put on them, not AMD. Now comes the 2200+, but for some reason AMD decided NOT to lock the cpu before they shipped it. And this is when the stuff hit the fan. Many could not get the cpu to boot in their machines, so they started tinkering with the L3 bridges. The solution was real simple, but it was beyond them I guess, and the L3-5 myth roared it's ugly head. The most rediculous thing I saw this called was the Magic bit that unlocked the cpu. As the 60 minutes guy would say, give me a break. If you want to understand this more, here's a good link.
http://www.beachlink.com/candjac/TbredDecode0.htm#Table

So now that you know the problem, what do you do about it if you have a board that doesn't support all the multiplier bits? Well, I list some work arounds in order of ease to do IMO.

1. Cut the L1 bridges. This will allow the cpu to operate at it's default multiplier setting. Which you can change on the cpu fairly easy if you want.

2. Some board makers will rma the boards and modify them I'm told. I have no personal knowledge of this and I don't know if there's a charge.

3. Close L3-5 bridge if you can live with a maximum 12.5 multiplier. In this case, to attain max speed, your FSB must support 166mhz or higher.

4. This is just a theory. I make no claims as to doing it. Cut the trace to the .5x multiplier pin and move it to the 8x multiplier pin (AJ27) on the socket. This would do away with the half steps in the multiplier and should give you 5=5, 5.5=13, 6=6, 6.5=14, etc.

5. The most control, but by far the most work required. Cut ALL traces to the multiplier pins on the motherboard and wire them to dip switches. This will require knowing what you are doing. The above link should help you if you decide to take this somewhat drastic means.

6. And I almost left this out. Get a new board that has proper support.:-)

So there you have it. Comments and corrections welcome.

Update 12/05/03: CPU's with a date code of 0339 and later are being multiplier locked internally by AMD. Since the multiplier can't be changed via any method at this time on these locked cpu's, you will only be able to run the cpu at default multiplier times the max FSB speed you can get from your motherboard.