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| Overclock LC475/P475/Q605 without soldering or spicy-o-clock |
Posted by: Renegade on 2025-05-02 07:37:12
For some unknown reason, the Soft475 extension doesn't work on my CC Mystic. It is crossed out in red during start-up, as if it didn't recognize the machine. The control strip doesn't work either.
My Mystic doesn't have the VGA mod and boots with patched systems (gestalt 99 edited from 21 to 10 in the ‘gusd’ resource) to allow 512x384 mode. |
Posted by: Renegade on 2025-05-03 05:43:35
For some unknown reason, the Soft475 extension doesn't work on my CC Mystic. It is crossed out in red during start-up, as if it didn't recognize the machine. The control strip doesn't work either.
My Mystic doesn't have the VGA mod and boots with patched systems (gestalt 99 edited from 21 to 10 in the ‘gusd’ resource) to allow 512x384 mode. Well, it was that simple. With the aforementioned modification to the System file, the Gestalt ID returned by the machine is ‘99’, which corresponds to the LC 580. And the Soft475 extension doesn't accept this, quite logically.
However, it is possible to work around the issue via Wish-I-Were by forcing the Gestalt ID to 92 (=LC 575) and this time the Control Strip is happy and modifies the CPU speed as expected.
I assume that most Mystic owners who tested the software overclocking had already made the VGA mod. |
Posted by: christcc2 on 2025-05-22 09:59:50
Well, it was that simple. With the aforementioned modification to the System file, the Gestalt ID returned by the machine is ‘99’, which corresponds to the LC 580. And the Soft475 extension doesn't accept this, quite logically.
However, it is possible to work around the issue via Wish-I-Were by forcing the Gestalt ID to 92 (=LC 575) and this time the Control Strip is happy and modifies the CPU speed as expected.
I assume that most Mystic owners who tested the software overclocking had already made the VGA mod. That is the case for me. I've got the VGA mod and this is running successfully for me. |
Posted by: frontein1 on 2025-09-09 16:44:55
This is just such a great thread, I wanted to link it to this other one regarding ROM modifications. I borrowed from @Mustermann the hack to skip the onboard RAM and the LC475SetCPUClock program. However I made one mod to this program, and that was to set bit 3 from 1 to 0 for the Config register (40MHz setting). Since the v092 version of my ROM bypasses the onboard memory, I believe it is safe for me to run the RAM at 60ns instead of 80ns.
Anyway I posted an initial benchmark comparison on that thread of 33MHz (stock) vs 40MHz (mod). I am going to see just how fast I can push the system before it becomes unstable.
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Posted by: croissantking on 2025-09-10 17:04:01
If you've previously overclocked an LC475 to 33MHz by moving its resistors, do you have to move them back before you can soft clock? |
Posted by: Powerbase on 2025-09-10 19:28:59
If you've previously overclocked an LC475 to 33MHz by moving its resistors, do you have to move them back before you can soft clock? No, it works fine on mine which had the resistor based overclock. |
Posted by: opualuan on 2025-09-10 20:19:41
My experience too- default boots to 33Mhz, but still can be adjusted. |
Posted by: DatMac on 2025-11-02 08:05:59
I have a lc575 with a daystar 601, sometimes i can get it to overclock a slight bit before it locks up but hoping the creator has updates soon for this unless there is already and i missed it. |
Posted by: croissantking on 2025-11-25 17:02:41
I recently picked up a couple of LC475 machines and tried out @Phipli's Control Strip Module – initially both topped out at 40MHz.
I upgraded one with a MC88916DW80 and it is now able to go faster. It's stable up to 45MHz, and crashes at 50MHz.
Configuration:
- 68040FE25 (L88M mask) on a PGA adapter
- MC88916DW80
- 70ns internal RAM
- 60ns RAM module
- 80ns VRAM
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Posted by: Phipli on 2025-11-25 17:30:25
I recently picked up a couple of LC475 machines and tried out @Phipli's Control Strip Module – initially both topped out at 40MHz.
I upgraded one with a MC88916DW80 and it is now able to go faster. It's stable up to 45MHz, and crashes at 50MHz.
Configuration:
- 68040FE25 (L88M mask) on a PGA adapter
- MC88916DW80
- 70ns internal RAM
- 60ns RAM module
- 80ns VRAM
Make sure you move the SCSI clock resistor. |
Posted by: croissantking on 2025-11-25 17:39:37
Make sure you move the SCSI clock resistor. I did (I forgot to mention it) 🙂 |
Posted by: opualuan on 2025-11-25 18:14:09
Nice work! With the same mods, this is as high as I’ve also gotten mine to work- faster vram didn’t seem to help. Any plans next, removing built-in ram? |
Posted by: Phipli on 2025-11-26 00:51:02
I did (I forgot to mention it) 🙂 Interesting - the timings in the control strip should mean that it's only a fairly small overclock on the RAM, ROM and VRAM at 50MHz (it has timings for beyond 40MHz in there). I suspect either the 88916 is struggling (could try swapping in a different, perhaps newer manufacturing date one), or try a different CPU. If that doesn't get you to 50MHz, you might have been very unlucky with the silicon lottery WRT the chipset on the board. |
Posted by: Joopmac on 2025-11-28 02:40:04
I have 4x 475, they are stable at:
38mhz with bolle’s diimocache
43mhz
47mhz
48mhz
They all have the 88920 swapped (from the same production/batch) Varying VRAM/RAM simm speeds but that is not the limiting factor, when I swap simms (or cpus) the results stays the same
Even onboard has differences but the slower/less ns RAM is the 47mhz board, the faster onboard RAM is on the 43mhz!
All meanwell converted (which is a great mod btw, especially in the dyna psus in combination with the printed bracket. I just desolder the wires with connectors from the dyna board and put them on the meanwell board. Hakko desoldering unit is really handy)
My next step is to swap 22.14mhz oscillator in my Quadra 700 with 40mhz 650 board as I don’t want the LCs to be faster then the Q’s |
Posted by: Phipli on 2025-11-28 06:58:11
I have 4x 475, they are stable at:
38mhz with bolle’s diimocache
43mhz
47mhz
48mhz
They all have the 88920 swapped (from the same production/batch) Varying VRAM/RAM simm speeds but that is not the limiting factor, when I swap simms (or cpus) the results stays the same
Even onboard has differences but the slower/less ns RAM is the 47mhz board, the faster onboard RAM is on the 43mhz!
All meanwell converted (which is a great mod btw, especially in the dyna psus in combination with the printed bracket. I just desolder the wires with connectors from the dyna board and put them on the meanwell board. Hakko desoldering unit is really handy)
My next step is to swap 22.14mhz oscillator in my Quadra 700 with 40mhz 650 board as I don’t want the LCs to be faster then the Q’s Generally you'll get higher clock speeds with the control strip than with the control panel. The control panel doesn't have the revised timings.
Have you swapped the SCSI speed resistor?
Other than the 88916DW80 mod, my LC 475 is pretty standard. 80ns RAM and Apple brand 80ns VRAM. It happily runs at 50MHz. I have a heatsink on the CPU and recommend running with the case on. I use the stock fan because there is more to fans than the free air volumetric flow rate. Has an actually under spec PSU because it has the lower power LC (not later power bumped one) PSU.
Also, having an ethernet card installed causes the fan to run faster in these machines interestingly. There is a pin on the PDS that detects a card and bypasses a resistor inline with the fan power to increase the fan voltage.
Surprised to hear people struggling to get up to 50MHz. Both my 475s, my 610, and my experimentation 650 all run at 50. RAM is the main issue on the other machines really, but that isn't a problem on the 475 because the timings are tweaked. |
Posted by: Joopmac on 2025-11-28 08:29:48
Pure copper Heatsink with printed duct, decent paste under it. The temperature is not the issue
The resistor has been moved
Yes I have farallon ethernet cases in all, btw! Curious if i lose 48mhz when i pull the card
My previous reply i ment slower ram with “more ns” instead of “less ns”, for the faster running lc; that was a bit confusing. Excuse me for that |
Posted by: Oliver_A on 2026-01-21 11:44:00
Hello there,
while I was running the Soft475 extension, I noticed the following issues during usage:
- Any screen resolution change flips the clock back at 25 Mhz (the default jumper clock setting)
- When using 40 MHz and switching to a 640x480 resolution, the pixel clock (which is also generated by Gazelle) seems to be wrong, so I get an "Out of range" message from my monitor. When testing the mode (e.g. by using SwitchRes), reverting back to the desktop resolution (e.g. 1024x768), and THEN switching back once again to 640x480, the pixel clock / refresh rate is correct, monitor can sync. But obviously, Gazelle has also now reverted back to 25MHz CPU clock settings
Do you think there is any way to work this around? |
Posted by: croissantking on 2026-01-21 11:46:47
Hello there,
while I was running the Soft475 extension, I noticed the following issues during usage:
- Any screen resolution change flips the clock back at 25 Mhz (the default jumper clock setting)
- When using 40 MHz and switching to a 640x480 resolution, the pixel clock (which is also generated by Gazelle) seems to be wrong, so I get an "Out of range" message from my monitor. When testing the mode (e.g. by using SwitchRes), reverting back to the desktop resolution (e.g. 1024x768), and THEN switching back once again to 640x480, the pixel clock / refresh rate is correct, monitor can sync. But obviously, Gazelle has also now reverted back to 25MHz CPU clock settings
Do you think there is any way to work this around?
This is a known limitation. Would setting the resolution before playing with Soft475 not be an adequate workaround? |
Posted by: Oliver_A on 2026-01-21 11:55:44
No, because I‘m using SwitchRes to define profiles for automatic resolution switching for certain games.
I suppose then that I should do the resistor mod instead, since everthing works great at 40MHz |
Posted by: croissantking on 2026-01-21 12:30:37
No, because I‘m using SwitchRes to define profiles for automatic resolution switching for certain games.
I suppose then that I should do the resistor mod instead, since everthing works great at 40MHz This seems like a good idea. Just be aware that the Gestalt ID will change and some software will not recognise it as an LC475 - but you can install ‘wish I were’ to get around that. |
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