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Mad With Macintosh


Upgrading a DOS Card With A Faster Chip

(Not Supported by Apple)

An Upgrade for the Mac 6100/DOS






These instructions are specifically for installing the Cyrix 5x86 and voltage

converter from ComputerNerd into a 6100 Mac. This procedure will apply to

all 61xx series PowerMacs. The procedure for installation the kits from Reply

and other companies, and into other Macs with Houdini II cards, should be





Static strap. Recommended but not strictly required.

CPU remover tool. Required, and included with the most kits, including the

one from ComputerNerd.

Screwdriver, or something similar that can be used as a lever.




Don't let the number of steps in the Procedure section scare you. It's wordy

because I want to be as descriptive as possible. After all, there is a potential to

damage your logic board, and this applies to any kit you use. But if I were to

be concise, I can sum up all the steps with the following:


1.Remove DOS card.

2.Remove original 486 CPU.

3.Insert new 586 upgrade assembly (CPU + voltage converter).

4.Install a low-profile heatsink, taken from the 486 being replaced.

5.Put DOS card back.


That's it! Now check out the nitty-gritty details below.





1.Turn off the power to your computer

2.If you do not have a static strap, leave the power cord plugged in. That

will provide a ground for discharging any static electricity. However,

unplug the power whenever removing or installing the DOS card from

the Nubus slot.

3.Remove the lid.

4.Before touching anything, attach the static strap to a bolt on the power

supply. Then attach the other end to your wrist. If you do not have a

static strap, touch the power supply's metal case. That will discharge any

static electricity to the ground. If you are working on carpet and do not

have a static strap, refrain from moving about much, and remember to

touch the power supply case often. This is very important in dry

climates or in Winter when the air is drier and static electricity forms

more easily.

5.Unplug the video cable from the back of the DOS card.

6.Unscrew the two bolts attached to the DOS card in the back of the case.

7.Unplug the CD passthru and audio cable from the DOS card. The cables

are two two identical flat ribbons to connect to two ports near the back

of the DOS card inside the case. Label these cables so that you know

where they go when you have to reconnect them later on.

8.Carefully lift out the card straight up.

9.Lay the card upside down on a flat work surface. The CPU should be

facing up and clearly visible.

10.You're about to touch a sensitive expensive component so touch the

power supply to discharge any electricity.

11.Remove the memory simm if you have one installed on the DOS card.

Snap the two clips at the ends outward, then pivot the simm forward. It

should come out easily without force.

12.See step 10

13.Use the chip removal tool to carefully remove the 486 CPU. Proceed


14.Note that one corner of the chip and one corner of the CPU socket

seems to be marked with a bevelled edge. Remember that corner - it's


15.You are now ready to insert the 586 upgrade assembly. By assembly, I

mean both the CPU and voltage regulator. Note the notch or symbol at

one corner of the assembly - it should align with the notch previously

mentioned. Insert the assemble carefully and evenly. If you see any bent

pins, stop immediately. Straighten the pin and try again, carefully.


At this point, there is a problem which arises from using the kit from

ComputerNerd and possibly some of the other kits, but not from the

Reply kit. The space in the 61xx case where the Mac CPU and the DOS

cpu normally sit is very cramped. Not only that, but the two CPUs are

directly opposite each other on two logic boards. Because of the

additional height from using the voltage converter, there will NOT be

enough room to insert the DOS card without the Mac's CPU heatsink

touching the 5x86 with a nontrivial amount of force. The following steps

show how to remove the Mac CPU heatsink and replace it with the one

attached to the 486 chip that was on the card originally.


16.Repeat step 10 to discharge any static electricity.

17.Carefully remove the clip attached to the CPU heatsink. Use a string or

plastic -coated twist-tie to pull each of the legs free. These pictures

should help:

Using a wist-tie.

Closeups of clip and clip+CPU to show how the clip works.

18.Lift the CPU heatsink off the CPU. There will be some white paste at

the bottom. That's heat-conductive heatsink compound. Don't get any

on the motherboard.

19.Detach the heatsink from the 486 chip that originally came with the

DOS card. It's being hell by a clip - simply pop each of the 4 legs of the

clip free.

20.Place the heatsink on top of the Mac CPU. There should be enough of

the heatink compound remaining to make the contact between the

center of the CPU (the square in the middle is the contact area) and

heatsink completely filled with the material. The heatsink compound is a

little tacky but use heat conductive tape if the Mac will be moved often.

21.Unplug the power cord.

22.Reinstall the DOS card.

23.Reconnect the CD passthru/sound cables to the DOS card.

24.Reattach the power and SCSI cables to the HD if you had detached


25.Reconnect the video cable to the back of the DOS card.



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