Quadra 605 build log

[zigzagjoe]

I've had the same experience. I've wondered if it has something to do with the tolerances of the RAM and/or VRAM I'm using.

If the machine isn't crashing, just not going faster, then you've hit the limits of the PLL chip. When they run out of overhead they just stop increasing in frequency.

 

[Fizzbinn]

If the machine isn't crashing, just not going faster, then you've hit the limits of the PLL chip. When they run out of overhead they just stop increasing in frequency.

This is the stock MC88920? Replacing with MC88916 like this would be need go hit higher speeds?

MOTOROLA MC88916DW80 SOP-20 IC DRIVER CLK PLL 80MHZ 20-SOIC | eBay

◆If there are no special circumstances, your product will not be delayed in arrival.

www.ebay.com

Upgrade MC88920 to MC88916 for LC475/P475/Q605 (advanced soldering)

In the Overclock LC475/P475/Q605 without soldering or spicy-o-clock thread I learned that LC475 can be pushed to the limit of the MC88920 by software, but to exceed this limit MC88920 need to be replaced by MC88916. There were some questions about availability and sources that can be discussed here.

68kmla.org

 

[zigzagjoe]

This is the stock MC88920? Replacing with MC88916 like this would be need go hit higher speeds?

MOTOROLA MC88916DW80 SOP-20 IC DRIVER CLK PLL 80MHZ 20-SOIC | eBay

◆If there are no special circumstances, your product will not be delayed in arrival.

www.ebay.com

Yes, to both counts.

 

[65a]

Well, I got the clock chip in nicely (please ignore the fact that tinfoil is insufficient to protect the plastics perfectly in this area). I can actually clock to 45mhz now, but I get a bus error at 50mhz. Haven't investigated that too much (or cleaned the flux off yet).

 

[Phipli]

Well, I got the clock chip in nicely (please ignore the fact that tinfoil is insufficient to protect the plastics perfectly in this area). I can actually clock to 45mhz now, but I get a bus error at 50mhz. Haven't investigated that too much (or cleaned the flux off yet).

View attachment 98627

You'll want to move R96 to the R95 position. It won't be stable without.

 

[shirsch]

You'll want to move R96 to the R95 position. It won't be stable without.

View attachment 98631

Is this mod strictly for the replacement PLL, or will it help stabilize software overclocking with the OEM chip as well?

 

[croissantking]

Well, I got the clock chip in nicely (please ignore the fact that tinfoil is insufficient to protect the plastics perfectly in this area). I can actually clock to 45mhz now, but I get a bus error at 50mhz. Haven't investigated that too much (or cleaned the flux off yet).

Similar to my experience. I need additional cooling on the CPU to stay stable at 50MHz. 45MHz is far more tolerant.

 

[Phipli]

Is this mod strictly for the replacement PLL, or will it help stabilize software overclocking with the OEM chip as well?

It relates to the SCSI chip - the default setting is only intended for 25MHz. Even at 33MHz the other position is what is recommended.

Basically you'll get crashes if you do longer copies or decompress a file or use a scanner or whatever if you push the speed too far without moving the resistor from R96 to R95.

Assuming the CPU can do the speed anyway, but regardless, the resistor needs moving because it will be causing issues, even at speeds less than 50.