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Macintosh LC III Overclocking, 25Mhz to:===>33Mhz

NickNick

Well-known member
The other day, thanx to uniserver's tips and faith, I sucessfully OC'd three Macintosh LC III's all to 33 mhz and boy let me tell you...You really can see and feel the difference with everything. Robotron is 10x faster than before, tech tool pro loads quicker as well as the machine boots and shuts down faster. Its just faster all the way around.

It is so easy to do and is much worth it! Cant believe it took me this long to work up the courage to attempt this mod. Next.....the LC475 and Q605. :)

 

AbelVincze

Active member
I also did the Overclocking on my LC III, it seems to working, but have some side effects, and finally i'm not sure to keep it overclocked:

- When powering on the machine, just after a few seconds it "restarts" one time, i mean it gongs 2 times before booting.

- Some Benchmark apps, and the system itself doesn't recognize the machine (Unknown model)

To be honest, i'm only aware of the first issue, i really don't like this boot with 2 gongs... Anyone experienced the same issue?

 

uniserver

Well-known member
It might be possessed by a demon.

try preforming a séance, ask the spirits to help.

- what os are you running?

- so like if you restart it 5 times in a row… it will double bong every time?

- your pram battery is installed? and reading 3.6v?

- what size ram you have in there?

- how much vram?

- what is video resolution are you running?

- temps? any extra ordinary temperatures your seeing across any of the I/C's?

- solder work, were you extra careful and didn't get solder on anything else?

- 7.5.3+ Most of the time says Just |Macintosh| anyways with most models.

- i only get something like this with like 8.1 on my zip disk, when i boot it with a 68k, then boot it with a PPC machine… it will boot .. quickly reboot bong again.. and then boot.

that is only because i think its making a change in the system folder for that specific architecture.

- I'v personally over-clocked about 40 now, never had your issue.

- if you don't like it, then by all means reverse it.

- however, my experience, the bump in CPU and VIDEO performance has always totally been worth it.

 

Ike

Well-known member
My stock Performa 460 (LCIII) does that when I boot it without a PRAM battery.

Like it resets the PRAM then reboots the machine.

 

AbelVincze

Active member
Thanks for the help guys, it was the missing PRAM battery. Unfortunately after succesfully booted my Mac (with single gong), i went to eat, and when i came back, my 540MB HDD died:(

One last issue: A just replaced the HDD with the one in my LC, and MacsBug 6.5.3 isn't loaded in my Overclocked LC III. (As i didn't tested it before OC, i don't know if this case is related to the LC III itself, or the OC caused it). (System 7.5.3)

 

AbelVincze

Active member
Me again, i can now confirm, that applying this OC will prevent MacsBug to load at boot time. I liked a lot the additional speed, but as i want to use these machines for development, the OC is not an option for me. Tested OS, 7.5.3, 7.5.5, 7.6, 7.6.1

 

uniserver

Well-known member
What is MACSBUG?

Also the re-clock we'll call it, makes it a LC-III+

witch is a legitimate model.

are you sure you are not doing something odd?

 

AbelVincze

Active member
What is MACSBUG?
Also the re-clock we'll call it, makes it a LC-III+

witch is a legitimate model.

are you sure you are not doing something odd?
MacsBug is a debug console on the Mac, invoked by NMI (command-power btn) http://en.wikipedia.org/wiki/MacsBug

R14 soldered out, and soldered on the empty place R74... I tested the solderings, and as everything was ok finally (except macsbug, and model type recognition) i think the OC was done correctly.

 

LCGuy

LC Doctor/Hot Rodder
If you have a flat PRAM battery, or no PRAM battery and you're running 7.6, the double-boot is normal - the first boot puts the Mac into 32 bit mode (required for 7.6 or later), and reboots it.

 

unity

Well-known member
If its a 000 ohm resistor, would that not mean in fact its not really one at all? Basically a wire link. I know other Macs where instead of moving small resistors one could just create a solder bridge instead. The "resistor" was used simply because it was an easy part to drop in on the board when different combinations of connections applied to different speeds.

 

AbelVincze

Active member
I'm wondering is it possible to make an internal switch, so it would be possible any time to switch OC on/off...

 

unity

Well-known member
I'm wondering is it possible to make an internal switch, so it would be possible any time to switch OC on/off...
Yes, if its a 0 ohm resistor you could add a switch. They makes switches with multiple contacts that would effetely break one connection and make another in one flick.

 

techknight

Well-known member
Eww... keep those wire leads short if you use a big switch like that, otherwise youll end up with clock skewing and other weirdness.

 

techknight

Well-known member
it doesnt specify the maximum frequency at which you can apply through that switch before leakage becomes a concern.

 

mac512

Active member
I'm sorry to resurrect such a long dead thread.

I'm thinking of performing this upgrade. However, I'm concerned about the stress on the 25MHz CPU (mine is not a down-clocked LC III+ motherboard but the original with the 25MHz CPU). Would it be too much for the 25MHz CPU in the long run?

Thanks!

 

MrFahrenheit

Well-known member
I'm sorry to resurrect such a long dead thread.

I'm thinking of performing this upgrade. However, I'm concerned about the stress on the 25MHz CPU (mine is not a down-clocked LC III+ motherboard but the original with the 25MHz CPU). Would it be too much for the 25MHz CPU in the long run?

Thanks!
And again, sorry for ancient resurrection as well (this one only 7 months later):  I think if you attach some good heat sinks it would help with a hot CPU. I wouldn’t want to run this mod with full cpu usage 24/7. I plan to do this mod myself later this month and I’ll definitely be attaching some heat sinks. 

 

David Cook

Well-known member
Me again, i can now confirm, that applying this OC will prevent MacsBug to load at boot time. I liked a lot the additional speed, but as i want to use these machines for development, the OC is not an option for me. Tested OS, 7.5.3, 7.5.5, 7.6, 7.6.1

9 years later: Make sure the PRAM reset didn't put the Macintosh into 24-bit addressing mode. Newer versions of MacsBug will quietly not load in 24-bit mode. I can confirm MacsBug 6.2.2 works in both 24-bit/32-bit addressing, but 6.5.4 does not.
 
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