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How to Get All 66 MHz Slot 1 CPUs Running 100 MHz


In the first hours after posting this article I received several mails suggesting nail varnish instead. Indeed it may be an even better idea, since it's easy to apply and also easy to remove. Harvey Rubens also pointed out that adhesive tape can contain aggressive chemicals which could damage the contacts. He suggested the following:

One possible solution is "anti-corona dope," that red paint you see in
high voltage electronic equipment as an insulating paint. You could
try fingernail polish or a paint used for model aircraft. Any such
paint should be allowed to dry completely to prevent scratching of the
paint or accidental contamination of adjacent terminals on insertion.

Another possibility is the tape used to splice analog recording tape and
cassettes. This tape is very thin and is formulated specifically to
prevent the "bleeding" I mentioned, because, in the early days of
recording, this was a very big problem.


I have read your section on isolating the B21 lead on the Pentium II carTRidge. Suggestions you have listed are: nail polish, elecTRician's tape, anti-corona dope" high-voltage insulating paint, model airplane paint, or splicing tape for analog recording cassettes. I hesitate to use any of these methods because the constituent materials were not specifically designed for this type of use. Nail polish and model airplane tape may have small capacitances due to their dielecTRic behavior thereby creating an unstable elecTRical joint. Insulating paints, on the other hand, may have abrasive surfaces that will eventually wear down the Slot 1 mating connectors. In addition, thermal cycling and pressure may cause the interface between paints or nail polish and the B21 lead to fracture, causing flaking of the material. This result could be a short between neighboring leads.

While none of these problems have yet been observed, I have a simple and cheap solution that may eliminate all these potential issues. The answer? Teflon tape. Teflon is a unique material that has an exTRemely low friction constant, excellent dielecTRic sTRength (no leakage current), and is resilient to temperature fluctuations. In tape form, Teflon is relatively soft and can be easily sTRetched with ones hands. The smooth, soft surface eliminates abrasive problems and will conform to the B21 lead/Slot 1 contact. The tape can be applied and removed very easily unlike nail polish or paint. The operating temperature of Teflon is roughly -100 F to + 500 F (-70 C to + 260 C) so thermal cycling should not pose a problem. For an example of Teflon's use in isolating elecTRical components, one need look no further than Granite Digital ( ), a premier SCSI cable supplier. Their cabling is considered the best by many and uses Teflon instead of the standard PVC.

To purchase Teflon tape (in the US) contact McMaster-Carr at . I have listed tape rolls and their corresponding features/price below. The tape comes with an 1.5 mil thick (1 mil = 1/1000th of an inch) silicone adhesive, and for the product numbers listed below, the width is 1/4". Other dimensions are also available from McMaster-Carr. According to their catalog, there is no order minimum so if you want just one roll, you can get just one roll.

In case you decide to post this, Tom, please add this:

Users attempting to use Teflon tape on their systems do so at their own risk. I will not be held responsible for any problems or damage resulting from this suggestion.

Brent Clothier

P.S. Great job on the BX Review! Thanks for your hard work. It is sincerely appreciated.

Tape ThicknessProduct NumberPrice(per roll)Dielectric StrengthTensile Strength
2 mil76475A11$5.738000 V25 lbs./in.-width
3 mil76475A16$6.5310000 V25 lbs./in.-width
10 mil76475A17$13.8419000 V50 lbs./in.-width

For those interested:

The dielecTRic sTRength should be the voltage applied through the thickness of the tape at which the insulating properties severely degrade and current starts to flow. I say "should be" because no procedure was given in the catalog on how these numbers were obtained.

The tensile strength is the stress per width of the tape required to make permanent deformation in the tape. The "per width" should be obvious since wider tape is stronger. Thickness is also important as can be seen from the 50 lbs./in.-width for the 10 mil tape as opposed to the 25 lbs./in.-width for the 2 and 3 mil tapes.

You can also try and break the line to B21 on the CPU PCB (as I didn't dare to write, but as suggested by David Klepes), this would obviously be irreversible unless you want to re-solder it later, which will at least be visible on Celeron CPUs. Whatever you want to use, it simply has to isolate 'B21' from its Slot1 connector.

Good Luck !