LC520 Overclock

[Drake]

In regards to the LC520 (68030 @25mhz) it can often be overlooked in favor of the LC575 (68040 @33mhz).
For those unaware these motherboards are a convenient direct swap-in replacement for the sluggish Color Classic motherboard (68030 @16mhz).
*While I am not in favor of cabalistic practices, I do happen to have the models mentioned above and will swap them for fun.*
The following is a simple, quick and easily reversible mod to bump the LC520 from 25mhz to 33mhz (likely what should have been done in factory) but we won't get into Apples intentional sand bagging of systems.

The above resistors are all that stand in the way from unleashing your blazingly fast 33mhz!
simply remove R67, R75, R79.

Once completed your LC520 board may have an identity crisis and wish to be addressed as a "Color Classic II" with a 33mhz 68030!
Congratulations Speed Racer, you're at the front of the pack now!

 

[JDW]

Amazing info, @Drake!
No ill effects on serial port communication after those resistors are removed?

 

[Drake]

Amazing info, @Drake!
No ill effects on serial port communication after those resistors are removed?

Nope! If we look at the actual performa 275 (Color Classic 2) these resistors aren't installed from factory. Further evidence that the LC520 was just the Color Classic 2's big slow brother!

 

[JDW]

Nope! If we look at the actual performa 275 (Color Classic 2) these resistors aren't installed from factory. Further evidence that the LC520 was just the Color Classic 2's big slow brother!

Very interesting indeed!

I'm quite curious as to what the removal of those 3 resistors is doing in the circuit. Do you have a schematic?

The stock Color Classic motherboard is quite similar, but I'm guessing the same thing cannot be done on it. If it could be done, one wouldn't need to swap with an LC520 to get better performance.

 

[Mr. Fahrenheit]

Very interesting indeed!

I'm quite curious as to what the removal of those 3 resistors is doing in the circuit. Do you have a schematic?

The stock Color Classic motherboard is quite similar, but I'm guessing the same thing cannot be done on it. If it could be done, one wouldn't need to swap with an LC520 to get better performance.

Similar things can be accomplished with the LC575 and allowing it to work at 512x384 resolution, and the LC3 (overclock to 33mhz making it an LC3+), and the LC475/Q605, which can be overclocked easily to 33Mhz from 25mhz.

 

[Drake]

Similar things can be accomplished with the LC575 and allowing it to work at 512x384 resolution, and the LC3 (overclock to 33mhz making it an LC3+), and the LC475/Q605, which can be overclocked easily to 33Mhz from 25mhz.

I have done the overclock to a couple pizza boxes as well, a marginal improvement but why not!? On the '040 machines I usually add a heatsink just in case but typically those units don't get too hot.

 

[Mr. Fahrenheit]

I have done the overclock to a couple pizza boxes as well, a marginal improvement but why not!? On the '040 machines I usually add a heatsink just in case but typically those units don't get too hot.

I bought a LC475 board on eBay last year that had a 128MB SIMM and a full 68040 33mhz on it. I think I paid $125 USD for the board with RAM and the CPU. I recapped it, and cleaned it up, and of course OCd it to the 33mhz the CPU was made to run at. I put heat sinks on all of the chips that warm up, not just the CPU. I then put a 36GB SCSI drive (using a SCA80 to 50 pin adapter) and a PDS ethernet card into it. It's my go to machine besides my Q650.

 

[alxlab]

Just thought it might be useful to also have a reference of the original source of the mod:

https://web.archive.org/web/20160416050801/https://www.thinkclassic.org/viewtopic.php?id=600

The mod is very similar the the LC 630 / LC 580 mod. Makes you wonder if there's any other boards that might have similar undocumented abilities

 

[Fizzbinn]

In regards to the LC520 (68030 @25mhz) it can often be overlooked in favor of the LC575 (68040 @33mhz).
For those unaware these motherboards are a convenient direct swap-in replacement for the sluggish Color Classic motherboard (68030 @16mhz).
*While I am not in favor of cabalistic practices, I do happen to have the models mentioned above and will swap them for fun.*
The following is a simple, quick and easily reversible mod to bump the LC520 from 25mhz to 33mhz (likely what should have been done in factory) but we won't get into Apples intentional sand bagging of systems.
View attachment 22
The above resistors are all that stand in the way from unleashing your blazingly fast 33mhz!
simply remove R67, R75, R79.
View attachment 23
Once completed your LC520 board may have an identity crisis and wish to be addressed as a "Color Classic II" with a 33mhz 68030!
Congratulations Speed Racer, you're at the front of the pack now!

Awesome, I had been thinking about whether this might be possible after noticing how similar (seemingly identical) the LC520 (25MHz) logic board is to the LC 550 (33Mhz) and Color Classic II (33Mhz) logic boards (which seem identical themselves except built in VRAM?).

The similarity reminded be of the LC III (25MHz) and LC III+ (33MHz) boards where you just need to move a resistor to turn a III into a III+ and the base LC520/LCIII architectures appear closely related looking at the apple dev notes.

I got a LC520 board in a trade a while back and while it works in the Color Classic (I call it a Color Classic+ I definitely will try this out!

 

[Fizzbinn]

The stock Color Classic motherboard is quite similar, but I'm guessing the same thing cannot be done on it. If it could be done, one wouldn't need to swap with an LC520 to get better performance.

That would be nice, unfortunately you are correct, the Color Classic board's base architecture is from the LC/LC II. The LC III architecture used in the LC 520/550 and CC II, is quite different/improved (32 bit bus, 72-pin SIMM RAM with no 10MB limit, etc.).

One thing that the LC520/550 (and 575 and up) boards have over the LCIII is support for stereo sound, I'm pretty sure I saw a mod for the Color Classic analog board where you can "fill-in" missing components and add second internal speaker to get a Stereo Color Classic!

 

[JDW]

I'm pretty sure I saw a mod for the Color Classic analog board where you can "fill-in" missing components and add second internal speaker to get a Stereo Color Classic!

Actually, the Stereo Mod is on the agenda for my Color Classic video series, and I've already acquired the second speaker. But I intend to do the 640x480 and overclocking videos first. Stay tuned!

 

[Fizzbinn]

Actually, the Stereo Mod is on the agenda for my Color Classic video series, and I've already acquired the second speaker. But I intend to do the 640x480 and overclocking videos first. Stay tuned!

Oh great, can't wait!!