Diode delay problem? I can't say I've heard of that. This one is kind of complicated, but I'll go over it anyway to clear up the issue:
Up until the Athlon XP (palomino core) and Durons at 1 GHz and higher (morgan core) the K7 core lacked a thermal diode. The root of the problem with Athlons burning up was that the temperature detection and overheat protection was done via software (firmware in the bios to be exact). This worked, but could not react fast enough should the heatsink fall off or not be attached. It worked fine if a fan failed. When the Athlon XPs came out (with the thermal diode) 2 pins on the socket were set aside for it. (These pins were previously unused.) Existing socket A boards of course could not take advantage of the addition of the thermal diode, and newer boards did not immediately either.
In case you are wondering what a "thermal diode" is, I'll explain them briefly. (DejaVu probably already knows this.) In actual fact, any diode can potentially be used as a thermal diode. All diodes have a so called "built in voltage" (Vbi) (can be roughly thought of as the voltage at which a diode "turns on") which varies somewhat with temperature. At room temperature a silicon diode typically has a built in voltage of around .6 to .7 volts. That voltage increases as temperature increases. By monitoring this voltage, temperature can be determined. (For those who really want to know, I'll give you the exact equation to determine Vbi later on.) There is no significant "time delay" present.
The "fix" was simply to use a hardware based circuit (a comparator) to compare the voltage across the diode with a reference voltage. When the voltage across the diode exceeded a certain level, power is cut off immediately. As I said above, all Athlon XPs and Durons >= 1 GHz have a diode onboard which can be used for this, but motherboard manufacturers simply did not implement the neccessary hardware to take advantage of it. That Tom's Hardware video was a great thing, as it forced AMD to take action to correct the problem. Asus and Soltek retrofitted all their socket A boards to include a hardware monitoring circuit within a month of the video's release.
The equation for Vbi is:
Vbi = kT/q * ln ((Na*Nd)/ni^2) k is Boltzmann's constant which is equal to 8.617E-5 (units are eV/K). q is the the charge of an electron = 1.6E-19 Coulombs. T is the temperature in degrees Kelvin. Na is the related to the doping concentration of acceptor (P type) impurities. Nd is related to the doping concentration of donor impurities (N type). ni is the intrinsic carrier concentration of silicon, which is usually around 10^10. For a given diode, all except temperature are constants once the diode is made. As the equation would indicate, Vbi increases as temperature increases.)
