CPU BRIDGE MODDING GUIDE

CPU BRIDGE MODDING GUIDE

Updated 05/11/02 by Tim B @ OCWorkbench.com

(Part of Modding Guide found here...K7S5A Board Guide)

Disclaimer - Perform these at your own risk and only if you know what you are doing and are competent with internals of you computer case. Always ensure that the power is switch off after use, and remember PSU's store power shortly even though they have been switched off.

Blowing the bridges using a PSU.

This method is useful when cutting the bridges using a knife or similar doesn't work,

This method can be used to open the gold bridges on the cpu, I used an old 300W ATX power supply, because it was an ATX power supply it needs a motherboard to turn on, you can trick into thinking it plugged into a mobo by connecting the green and any black wire using a bent paperclip - not required for non-ATX psu's.

See image below from the psu faq.

Then I used the 12v line (apparently this method also works with the 5v line - but I used 12v due to it have less ampage...

I dismantled the cd power plug by removing the metal 'casings' out of the plastic housing. This can be achieved by pushing a small object in the end next to the metal clip and bending it in slightly so that it slides out of the end of the plastic plug

Then I used two pins, the pin head slid nicely inside the now exposed metal case for the wiring. To tighten the grip I flattened it slightly with some pliars so that a firm connection was made between the pin and the wire.

For 12v use the yellow line and any black line.
For 5v use the red line and any black line.

It may also be a good idea to try and insulate the wire around the connection between the pin head and the metal wire so as to not come in contact with it.

Then with the PSU turned on, you touch one end of the pins to the bridge, being very careful not to touch anything else, then touch the other lead to the other end of the bridge. Hold them there until a spark appears and the bridge should have been successfully blown.

You can test it with a digital multi meter, if it isn't blown properly then repeat the process,

Note: it is important to try and practice this method on an old bit of circuitry to see how long it takes to blow a bridge.

And remember to turn the psu power off after the bridge has been blown, I found this method a lot easier and cleaner than trying to cut the bridges with a knife on my Tbird, one word of warning however - DO NOT touch any other part of the cpu apart from the bridge your are trying to blow. This is very imporatant and I suffered by losing some of my L2 cache due to accidental contact with the L2 bridges.

My previous experience: http://www.ocworkbench.com/ocwbcgi/ultimatebb.cgi?ubb=get_topic&f=37&t=000174

Tim B.

General Tips By Yumosh
If your want to try "blowing" the bridges here is some general advice.
1) Keep the voltage and the amps low. A higher voltage will cause a higher current draw through other circuits in the chip (the contacts have an impedence of about 2k to each other or the signal bus). If you can find a pwr supply to do 1-2 volts and 5 amps - great. I don't think you need more than 5 amps to melt the bridge so a higher value might cause too violent of a reaction and possibly damage the bridge too much (if you wish to reconnect it later).
2) Use needles or pins at the ends of your leads and don't keep contact to the bridges longer than you need to see the small spark as the bridge melts and arcs.
3) Don't touch any other contacts. If you don't have a steady hand let someone else do it.
4) Clean up the bridges with isopropyl alcohol to get rid of any carbon traces and any melted copper debris.
5) Remember... you are short circuiting your power supply through your chip. You may encounter a poor trace inside the chip that fails before the bridge blows (read: fry your cpu) or damage your power supply.

Unlocking the AXP CPU Guide

Origingal thread.
http://www.ocworkbench.com/ocwbcgi/ultimatebb.cgi?ubb=get_topic&f=22&t=000644

By Iggy

As many people want to cut their bridges in order to change the multi of their CPU (that can be dangerouos task), I decided to write down a simple, fast and secure procedure of unlocking the AXP that will work extremelly well in conjuction with Multi-Lite mod found on these pages. (Multi Mod Guide)

What you'll need:

Tipex (or wite correction fluid, liquid paper)
Ohmmeter (either analog or digital, here shortly, DMM)
Cotton bud (or a straw, or toothpick)
Deffoger repair paint

I use a kind of small straw, that is sharpened at the end (I actually use the small plastic tube from the cotton bud, ). In this way it acts as a simple writing pen.

Just fill the pits with this self-made pen with a small amount of tipex on it, and while filling them, spread it around in order to keep it as flat as possible.

Any excess can be wiped out with the piece of plastic (or toothpick, never use any sharp edge or metal, it really easy goes off) after drying, making sure that the dots are clean (use a toothpick for cleaning the dots).

Then check with the DMM that there is no contact on the top of the filled pits with any of the writing (AMD, fe, that is connected to GND) on the CPU, to be sure that when applying paint it want short out that bridge.

Connect black(-) test lead of the DMM (in the range of 0-2(5)KOhms) to those writings, and swipe the red(+) test lead over the filled pits. If the resistance is high, you may proceed. If the resistance is low, you will need to reapply Tipex.

Paint is then applied with the other sharpened end of the straw.

I usually make a small (!) blob over the first, third, and fifth bridge, and leave it for a few minutes to dry out.

Then those bridges are checked with the DMM.

They must have resistance from both sides of newly made bridge towards GND (writings!) of around 240 Ohms.

I then paint the remaining two bridges.

If there is any overlap of the paint with any of the first three painted bridges, I make a small cut in that area (using a toothpick, or a scalpel, but you have to be very, very careful with it), so that there is no visible contact remaining.

Again checking with the DMM will reveal success or failure.

After this test has passed, it is important to check that the adjacent bridges are not shorted between themselves with the DMM.

The resistance between the painted bridges is around 480-500 Ohms.

When this test is successfully passed, I proclaim bridge modding a success, and the CPU is ready to be put through MoBos paces...

The defogger paint, as well as Tipex, can be rubbed away easily with a toothpick.

I unlocked very successfully a lot of AXPs, and I have to say that the paint keeps vey well under high CPU temps.

The whole procedure last around 10 minutes (but please do take your time!).