Succesful LC III upgrade!!

3 replies [Last post]
iamdigitalman's picture
Joined: Mar 2 2004
Posts: 629

It's offical, I just speed bumped my LC III from 25mhz to a blazing 33mhz. I did so by switching resistor R14 into the blank R74 on the undercarrage. I re hooked up, booted, bong, load, and then I ran Apple Personal Diagnostics (want it? PM me.) although, it now is called a Performa 406 in APD rather than the Mac LC III like before. I wish I could bump it to an 040 processor. is there a way? I think I saw one at the end of the service manual (googled for it). also, the mobo is a Revision D, but it says (c) 1992. why? oh, almost forgot teh specs:

Macintosh LC III
Motorola 68030 '68LC30' @ 33mhz
36mb ram
standard VRAM (I want more!! )
250gb conner HD 50 Pin SCSI inside
original 80mb Quantim 50 Pin SCSI outside (I have it in a hand build LEGO chassis) (the next compubrick accesory?)
Daynaport 10T ethernet PDS card
System 7.5.5 Revision 2

btw, I will post pics as soon as I can afford a digi cam.

P.S. the ethernet connection is odd. I can use PCMAC LAN to transfer files to it, but cannot connect to internet via same connection and iCab. why? I use a wireless hub, and have SBC Yahoo DSL with a 2Wire brand DSL modem. lemmie know about this one.

-digital Wink

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tmtomh's picture
Joined: Dec 20 2003
Posts: 568

Nice OC job.

The easy -- and only -- way to bump it to an '040 is to swap in an LC475 (or Performa 475/476, or Quadra 605) motherboard, which will fit perfectly and give you a 25MHz 040 CPU.

Then you have to OC that motherboard to get back to 33MHz.


Joined: Dec 26 2003
Posts: 584

But then, wouldn't the 25MHz '040 kick the living snot out of a 33MHz '030? I may be wrong... but I think if he did that overclocking it would have no real point...

tmtomh's picture
Joined: Dec 20 2003
Posts: 568
Yes and Not Necessarily

A 25MHz '040 would indeed leave a 33MHz '030 snotless Wink -- but one might still want to overclock the '040 motherboard. Going from 25MHz to 33MHz gives about a 30 percent increase in raw CPU speed, which might be worthwhile for some folks. Also, some folks just want to have an OC'd board, esp. here on 'fritter.