Improving the cooling of a Sun SPARCstation 20

Cooling a Sun SPARCstation 20.

First written in May 2003 by Dr. David Kirkby

The Sun SPARCstation 20 is to my mind a very nice computer. For its day, the amount of RAM it could take (512 Mb) and the number of CPUs it could hold was very good. At the time of writing (11th May 2003), Sun don't have a quad processor workstation available any more.

However, heat is a problem with the SPARCstation 20- packed with fast CPU(s) or modern disks(s), they just get too hot. Here are some suggestions to avoid system damage due to overheating. You might want to follow none or some of them. You won't be able to follow them all, since some are mutually exclusive. Any other suggestions from others are most welcome.
  1. Limit the number and types of CPUs. It is tempting to put in as many as possible, but they do generate a lot of heat. Take a look at The Rough Guide to mbus Modules to see what is sensible and what is not/
  2. Run headless, with no framebuffer, to cut down the heat generated.
  3. Don't use internal disks. If you can stand the clutter of external disks, they are a better bet
  4. Don't use the leo 24-bit framebuffer, as that generates a huge amount of heat. If you must have 24-bit, a VSIMM is a better bet.
  5. Removing sbus slot covers will certainly increase the airflow over the CPUs. This will decrease the amount of air over the disk. This will probably increase the amount of stray RF radiation and so violate FCC/EC regulations, so should not be done for legal reasons, despite the fact it does aid cooling a lot.
  6. Removing the left hand plastic side panel from the SS20 greatly increases the amount of air that can flow, but it does make the SS20 less attractive to look at.
  7. If you insist on using internal disks, try to use the slowest rotational speed you can. There is probably no performance advantage in using 10,000 or certainly 15,000 rpm disks, but such disks normally (if not always) generate more heat than slower disks. However, 10,000 rpms disks seem more common now - especially in the larger sizes.
  8. Unless you really do want an internal CD-ROM (they are far too slow to really install Solaris unless you have the patience of a saint), don't have a CD-ROM drive, but mount a larger fan blowing air over the disk
  9. Consider fitting at system to shut off the power to the disk if it overheats. Ideally a software solution that shuts the machine down gracefully would be nice, but I know of no such solution that is free. Commercial solutions only work for Solaris, not GNU/Linux or anything else you might put on your SPARCstation 20. The following describes the method I use. I take no responsibility for anyone doing this. Done incorreclty it could be dangerous. It would be easy to damage your SPARCstation 20. Only attempt this if you feel 101% confident about your abilities to do this.
    • Obtain a 4-pin extension lead (with two black, a red and a yellow wire) for power to a nomal disk. These are readily available from any PC shop. Ensure it has a male connector at one end and a femal at the other.
    • Cut the red wire (+5V) in half.
    • Insert a normally closed thermostat using a bi-metallic strip with an opening temperature of 50 deg C. I bought mind from RS components in the UK (stock number 229-5907) at a cost of under 2.00, but any decent professional electronics distributor will sell them. They are not the sort of thing you will probably find at Maplin or other retailers aimed at the hobbyist market. You will need to either solder this (as I did) or use spade connectors. Either way, use heatshrink tubing (best option) or electrical insulation tape to make the connections insulated.
    • Remove the 4-pin power connector between the small PCB into which the SCA disks plug and the power supply. It's a bit hard to undo, but does come out okay.
    • Insert the extension lead (with the thermostat) between the PCB and the original power connector. Hence no wires are cut on the SS20 - you have just added a normally closed swiched in the +5V rail.
    • Glue the thermostat onto the disk somewhere near the middle. If the disk is under warranty, think about what you use to attach the thermostat.
    • Here's a photo of the system with the thermostat fitted.
      Modified SPARC 20
      Should the disk get too hot for any reason, the switch will open and the operating system crash. I'd rather a crashed operating system than a dead disk. Unless the temperature drop quite low (35 deg C for the swich I used), the themostat will not open, so power will have to be removed for some time before the disk will run properly again. This will probably offer some protection to the CPUs too, since if a fan has failed and a disk gets too hot, it might stop the CPU cooking. However, Murphy's Law states the CPU will get too hot before the disk. This mainly protects against the faillure of the fan that cools the disk.
    • Note, only the 5V power line was removed by this - not the 12V line. The 5V controls the logic and removing this spins the motor down, dropping power disipation to near zero - at least on the disks I've tested this on.
  10. Keep the system in a location with plenty of air. Don't put seveal SS20's in a small room and hope they won't cook.