LC III+ is downgraded to 25MHz?

[djhaloeight]

Hey all. I was futzing around on my LC III+ the other day and ran TechTool Pro and noticed my gestalt ID is 27, not 62 as a "real" LC III+ should be. I'm running System 7.1 with the correct enabler. My "About This Macintosh" dialog box says Macintosh LC III as well. My machine has the newer case with non auto-inject floppy, my processor is a MC68030FE33B. I've always assumed this was a 33MHz LCIII+, but this YouTube video I just saw made me wonder otherwise:

In it, the guy says these models are "crippled" for lack of a better word and aren't actually running at 33MHz. Is this true?

Uniserver, maybe you can chime in. You recapped my board. Is this a real 33MHz LCIII+ or do I need a move a resistor like the video shows to unlock it's full speed potential?

Thanks for any replies.

 

[Elfen]

Some of the LC IIIs came in (newer) 33MHz and others (older) in 25MHz. I do have both but the 33MHz one is dead. For what ever the reason, they decided to continue making the 25MHz one while making the 33MHz one, so it ended sharing the same cases and same. The only difference between the two machines is just a crystal and a couple resistor jumpers. Nothing more. It is not, lets say, like the LC II. Now that is a crippled Mac!

EDIT: Read the Crystal (there are two of them), the one you are looking for should say 33MHz or 25MHz. If it says 25MHz, it needs to be swapped out with a 33MHz, and a couple of resistor jumpers changed.

 

[djhaloeight]

Crystal? I've never heard of a crystal for over/underclocking an LC III.  My processor is 33MHz.  From what I understand you just need to move a resistor from one spot to another on the board to overclock...I have no SMT soldering skills whatsoever so I'm not plannig on doing this mod myself.

 

[uniserver]

yeah basically the LC-III and the LC-III+ are the same board.

and what is funny is some LC-III+'s came with a 25mhz cpu and some LC-III came with a 33mhz cpu...

witch makes it that much more funny.

to make a LC-III an LC-III+ you move one resistor from the front of the board to the rear of the board.

and that is it.

http://www.applefool.com/clockchipping/lciii.html

 

[Elfen]

On the LC III board, there are 2 crystals. One for General I/O Clocking and the other is for the CPU clocking:

See:

http://www.applefritter.com/node/2130

(Y1 on the upper area above the empty FPU I believe is for general I/O and Y2 above the row of RAM is for the CPU)

It should be Y2 either a 25MHz Crystal or 33MHz Crystal. Mind, I do not have the LC III board on my lap to directly tell you , but I do remember the difference between the two is the crystal and a couple of resistor jumpers. Nothing else is different between them, not even the ROMs.

 

[djhaloeight]

Yeah I get that they're exactly the same board but I just don't understand how my CPU is a 33MHz model but running at 25MHz. Sounds like typical 90s Apple stuff

 

[djhaloeight]

Perhaps I can send it to you Uni, to get a proper speed bump to 33MHz While I'm at it I can send my slowly dying LC II for a cap job. I'll email ya about it

 

[Elfen]

Yeah I get that they're exactly the same board but I just don't understand how my CPU is a 33MHz model but running at 25MHz. Sounds like typical 90s Apple stuff

Why don't you look at the "resistor" placement of your LC III Board and see it "That Says" its either a 33MHz or 25MHz board? Just looking at the CPU label wont tell you anything because you can get a MC68030E25B to run at 33MHz and a MC68030E33B to run at 25MHz. The only way to be absolutely sure is to put a Clock/Frequency Probe at the CPU's Clock Pin and actually read the clock frequency from there. Only then can you absolutely say that this LC III is a 25MHz or 33MHz machine.

Added Material for your information indigestion...

Crystal Y1 on the board is  standard clock frequency oscillator at 32.768 KHz. This frequency is used for a lot of things from calculators to microwave ovens. So as I stated - Y1 is not for the CPU's frequency, it is too slow for it. 1000X times too slow.

It is Y2 that determines the CPU's frequency. On my LC III it has a tag of "0107T3G." Looking that up got me no where, except for some stupid Nissan Auto Parts Dealer for a Headlight parts' number. The LC III Schematics would state what frequency that crystal is running.

 

[uniserver]

yeah i even herd of some 25mhz LC-III's with a 16 mhz cpu.

i didn't believe it until i saw a picture of it.

 

[Gorgonops]

It is Y2 that determines the CPU's frequency. On my LC III it has a tag of "0107T3G." Looking that up got me no where, except for some stupid Nissan Auto Parts Dealer for a Headlight parts' number. The LC III Schematics would state what frequency that crystal is running.

No.

Here is the text from the LC III's Developer Note:

"Omega is a custom programmable phase locked loop clock generator that provides the primary clocks required by the Macintosh LC III. Omega produces a hardware-selectable system clock for the microprocessor bus, a programmable dot clock for the video circuits, and a fixed 31.3344 MHz clock used for the serial ports, sound circuits, floppy disk, and various timers".

IE, the LC III uses a synthetic PLL clock circuit to derive a bunch of different frequencies off of one crystal. Circuits like this started to become common as early as 1990 or so in PCs, where the same generic motherboard might need to be fitted with a 386 or 486 chip running at anywhere from 16mhz to 50mhz. Machines fitted with such chips do *not* have to have a crystal swapped out in order to change their speed as long as the clock generator circuit supports (via jumpers/resistors/whatever) different multipliers.

 

[djhaloeight]

yeah i even herd of some 25mhz LC-III's with a 16 mhz cpu.

i didn't believe it until i saw a picture of it.

Interesting! Well perhaps when my tax money comes in you can speed bump it for me to 33MHz

 

[uniserver]

 

[register]

The LCIII also sports a socket for an 68882 co-processor. I got one for free from a dead PowerBook daughter board (it fits the socket after cautiously unsoldering the FPU from the PB's daughter board). After clocking the LCIII to 33 MHz the case plastics of this 68882 melted. I glued a heat sink to the co-processor and the unit runs stable, now happyily supporting some hardware-FPU-only software like DraftBoard. Due to the finding of the molten FPU plastics I mounted a heat sink to the CPU, as well.