Oct 24, 2021 correction:
In the text, it says that the chip was replaced with a 256KB card (M5M442256), but when I looked it up later, it was 512KB. I will correct it here.
23-year ago, a book called Doping Mac was released. At that time, 68K came to an end, and the rise of PPCs was causing a modding of old Macs in Japan.
I really loved the Masato Ota article. He was good at modding Color Classic and LC575, LC630, and LC475. I was especially surprised at the method of overclocking at that time.
68K CPU, which generates less heat than PPC, can be easily overclocked without a heat sink if it is about 30% higher. *This method is just a copy of Masato Ota, including myself.
Read before trying!
I take no responsibility for what you do in the material contained in my article.This includes work-related injuries and equipment damage. Be very careful with the work and make sure that you can always revert to the original condition.
1）About VRAMs. 70Ns is the best, but if you can't prepare it, prepare 80Ns. And even with the same 80Ns, it turned out that Mitsubishi chips have high durability. It is described in detail in the following chapters.
Also, I’ve never tried 100Ns but I imagine it's even less durable. Unless my interpretation is correct…
2）Take a HD backup. Also, the device may not be read due to an abnormality in the SCSI chip. If you are worried, you should buy more oscillator of about 16MHz. I use the socket method, so the exchange can be completed in 10 seconds and the original clock can be used.
Important point! : I'm not responsible for any failure caused by this modification. If you get an electric shock from my article or your important ColorClassic breaks, I take no responsibility also.
Modding concept
In the case of LC575, XC88916DW55 (or DW70) which is a clock driver is onboard, so this is the external clock of CPU. It is a programmable clock generator called 343s1135 that sends the clock to it(The actual oscillator used is Toyo's 197S0512). The clock received by the XC88916DW55 is 1/2, so it will be a 16.6MHz generator output in the genuine state. This time we will overclock this to 20MHz.
Usually, replace this generator to over clock, but this 343s1135 has multiple roles and cannot be replaced.
Therefore, by shutting off the clock input of XC88916 and adding the output of the amplification oscillator to that, the overclocking of this time is completed by adding the clock calculation. You can overclock the LC630 and LC475 with a similar approach.
It was over 20 years ago that I made this modification, and the can-type oscillator that I used at that time is no longer for sale in the Japanese market. So I tried using Epson's new programmable generator SC-8002DC. It operates at 5V(Vcc) like the onboard oscillator (4.5V~5.5V to be correct) and can be programmed with a dedicated writer for this.*It is small enough and is as large as an 8-pin IC. Of course, there are chip types with the same specifications.
This time, Epson SG-8002DC pre-programmed to 20MHz was used. Originally, the setting of 1MHz to 125MHz can be written with the Epson machine called SG-Writer. I purchased it from Akizuki Denshi, a long-established parts store in Akihabara. As mentioned below, I wanted to try the oscillator set to 21MHz, but I gave up because it is not sold in Akizuki. Of course, can make a special order, but the order is from 10 pieces. I didn't buy a program writer machine because it's expensive to use for this purpose only.
I think the oscillator can be anything that works. I'm also interested in an oscillator that can change the frequency with a potentiometer.
Work is easy
This SG8002DC is equipped with a base 8Pin IC socket. Solder this to a cut universal board and connect the three lines of Vcc, GND and Output. Vcc and GND are connected to the on-board oscillator to supply 5V(Same legs locations).
About Output, but I think this is brave …lol Need to lift 8pin (third from the right) in the bottom row off the Logic Board. If you do it poorly, the pattern will come off or leg will break, so need to do it carefully.
According to Makoto Ota, the legs that were cut with a nipper and the remaining legs were melted with solder and removed. Certainly, this method makes it easier to work, and if we want to put back it, we can also put back it by extending it to the leg. I worked the same way.
Sorry for bad image...
Wirings are easy. Later, I was pointed out by a friend and noticed that this method clocks up the CPU, Graphics and memory RAM at the same time, but serial, ADB, and SCSI seem to be running on the original clock bus.
Test start
The startup chime sounded at a good start ! Start as usual and do some tests. First, whether the clock is appropriate, whether there are any abnormalities in graphics or operation, etc.
In my test, it worked without any problems, but after playing for about 30 minutes, the symptom peculiar to the graphics card of the past year, such as dust on the orbit of the mouse, appeared. Since I had only 80Ns VRAM this time, I think this symptom probably occurred. I am looking for 70Ns VRAM now, but I can't find it easily…
So I decided to try the VRAM that was stuck in another LC575 board. The result is even worse, and the screen does not appear even after booting... The sound of reading the hard disk remains black screen.
VRAM should be 70Ns?
I searched for 70Ns VRAM on e-Bay but could not find it. Since 100Ns is out of the question, I decided to verify it with a different manufacturer of 80Ns.
In case of 80Ns Mitsubishi M5M442256AJ-80, it operates at 40MHz, but when it warms up, dust appears on the mouse cursor. So, I tried buying all kinds of 80Ns VRAM. I wondered if some of them had good overclocking resistance.The results are below(*All are 256KB VRAM SIMMs):
Chip maker / Result
TOSHIBA TC524258BJ-80 / X The video is not formed on the black screen even after booting.
Mitsubishi M5M442256AJ-8 / △ There is no problem for a while after starting. After a few minutes of fever, dust sticks to the orbit of the mouse cursor.
Mitsubishi M5M482128AJ-8 / ◎ It works stably!!!
Those overclocking on the LC575 say they need 70Ns, but do you know what it means?
VRAM runs at 1/3 the speed of the original clock, but if this is 80Ns then the chip limit is up to 37MHz. But with 70 Ns, the theoretical limit is 43 MHz.
The Mitsubishi M5M482128AJ-8 is the newest VRAM in this two-chip configuration. If you look at the printed PCB, it's probably manufactured in 1992. The only one in this is a 2-chip configuration, the others are 4-chip configurations. In my imagination,
I think the internal speed of this chip has increased considerably.
70Ns VRAM builds
When I checked the part number of the chip, I realized that the same part number was 70Ns. For example, if the end is -80 or -8, it has 80Ns, and if it has -70 or -7, it has 70Ns. This is the same for all manufacturers. Fortunately, I was able to find 16 chips called M5M442256AJ-7. I decided to use it and replace it with the existing Apple VRAM card.
The result was good. I wanted to clock this up to 42MHz, but I haven't got a 21MHz oscillator. I'll save the fun later.
68040 VS PPC601
The advantage of this overclocking is that you can install 128MB of memory. I used to use the PPC601 card with Mystic as well, but since it only recognizes 32MB of memory, to be honest, the 66MHz high clock is also unattractive.
However, 128MB of memory takes a long time to boot. It takes about a minute for Happy Mac to appear…lol This is because the OS checks the hardware before booting. So 64MB seems better if you can.
In fact, the optimized OS for PPC is OS 8.5 or later, so it seems that there is no software that can take advantage of its performance in OSs up to 7.6. Even with the clocked up 68LC040, the speed is sufficient, and when some games, which have a strong influence of the clock, are too fast to keep up with the eyes.
Actually I would like to install 68060, but it does not run on Macintosh because it does not have 68060 microcode. It seems that no one has ever written the microcode. I think that the adapter of 68030 to 68060 was released from a manufacturer called Sanhayato in the old days, but there is no information now.
Mods is a light poisoning, and I feel pleasant when I exceed the limit. However, when I finish the point where there is no more, I feel the emptiness at the same time. I have no choice but to spend the same feeling as when I felt that I could not get a powerful drug anymore…lol
It is well known that color classic is equipped with LC630 series logic board. The pinnacle of this is the Performa 6500 logic board. I once built Color Classic with a 6410 logic board.
However, if your Color Classic is in good conditions, you should avoid this modification. This computer is no longer in production and few are in existence. It's sad to see the contents of the chopped pieces. Please work cleanly at least! I hope that the next generation will have a job that will leave a great computer instead of leaving rubbish…
The above is what I have done and the verification results. Please let me know if you have any disagreements.