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Cooling down the SFD1001.

Hugo Holden

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A recent thread mentioned about how the 1541 drive with the internal power supply tended to run hot. So I wondered about my recently acquired SFD1001.

I had been using it for a few hours and it certainly does run very hot from the power supply area. It relies on convection cooling taking the air in at the bottom vents and leaving at the top. I could feel very hot air slowly coming out the top vents. It is not helped by the fact that the rubber feet on the unit are not very tall and the lower surface sits close to the bench surface and that problem is aggravated if the drive is on a soft mat.

Looking inside the drive, there was little room underneath to add a cooling fan, but some hope on the top.

I found I could make a satisfactory mounting system, by removing two of the pcb's mounting screws and replacing those with metric hex posts and mounting the fans on those, immediately below the top air vents.

I chose some 50 x 50 x 11mm thick 12v cooling fans and was able to mount them so they sit about 1 to 1.5 mm above the top surfaces of the IC's in the region below the upper case cooling vents. They are powered from the 12V supply on the front connector on the pcb.

To join the two fan bodies together I use a piece of 1/4" wide and 1.6mm thick brass plate, with 3mm threaded holes. The holes were tapped with a taper tap, not quite the whole way through, so the 10mm metric retaining screws, whose heads sit in the fan mounting hole recesses underneath, tighten up in the thread just as they tighten the metal plate to the fan body.

Also I made a small piece of pcb, 22mm x 25mm to receive the fan wires and support a pin assembly for a plug.

It only takes 2 screws to un-mount the whole double fan assembly and unplug it. There are no permanent changes to the SFD1001 at all.

I attached the pcb assembly to the fan bodies using 3-48 1/2 inch long screws, nuts & spring washers. They needed to be a low profile head and a nut that would fit inside the fan hole recesses underneath.

The 55 mm long brass strip is attached to the 20mm post with a 6mm long 3mm dia countersunk head metric screw. The idea being to keep the profile low as there is not much clearance. This whole twin fan assembly sits no higher than the surface of the main heat-sink, so like that, it clears the internal housing.

Now when I run the drive I can feel high speed only tepid air existing the case top which is much better. At some point I will put in a temp probe and find the difference with & without the fans plugged in. But it is already obvious it is a substantial improvement.

I kept a record of the geometry of the assembly, in the event of it being of use to anybody else wanting to add cooling to their SFD1001. The useful 1/4' wide & 1.6mm thick brass plate is made by K&S Engineering in Chicago, IL.
 

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As an aside, repair tech Ray Carlsen successfully replaced the internal p.s. of a 1541 with that of a modern p.s.. Now the 1541 runs much cooler!

Truly,
Robert Bernardo
Fresno Commodore User Group - http://www.dickestel.com/fcug.htm
Southern California Commodore & Amiga Network - http://www.portcommodore.com/sccan
Commodore Los Angeles Super Show - http://www.portcommodore.com/class

That would work, but being into Vintage computers I'm very fond of originality and I try not to make such extreme changes like replacing the analog supplies with SMPS's in vintage gear. Instead I try to find a way of getting the best out of what is there, even if it has problems. Most of my add on computer projects tend to use period correct IC's and parts for the "vintage fun".

The PET computer surprised me; without a cooling fan. It helps in the PET to have the large housing and the hot air rises under the cut-out under the VDU pcb and exists via the VDU's back vents and under the rear lower VDU surface. The air leaving those vents is substantially hotter than what the VDU heat dissipation generates on its own. So they get away with plain convection cooling despite the large analog regulator system.

In the SOL-20, they had a very good line powered cooling fan, yet because of the compact nature of the housing and the close vertical stacking of the S-100 boards, along with their 7805 regulator IC's on individual S-100 boards, they get very hot in that area between the pcb's. I added an additional fan (a fully reversible modification) to blow air between the S-100 boards in my SOL-20. Some people have tried replacing the 7805's on S-100 boards with modern switch-mode drop in replacements, but these to not have the very clever and effective thermal and short circuit protections that are intrinsic to the analog 7805 regulator design and they generate interference spikes on the voltage rails. I have never warmed to that solution (no pun intended).

I'm not shy to use modern SMPS's though, especially for a new construction project. I used them to power disk drive pairs for my SOL and the cooling is ok by convection. As I mentioned in this article, the better places for slots for convection cooling are on the instrument's bottom surface and high up on the vertical sides, this way a lot less dust settles in the unit compared to having slots or holes on the horizontal top surface. Also people don't accidentally put objects over the vent holes, like they often do when they are on the horizontal top surfaces. It is also important the bottom surface is separated well from the table surface with good height cabinet feet, or the lower vents can get occluded, there are many traps for the unwary:

 
It is also important the bottom surface is separated well from the table surface with good height cabinet feet, or the lower vents can get occluded...
Back in the day, I would elevate my 1541 off the top of the desk by using a plastic spacer from a car battery, and so, air would circulate more easily through the bottom of the disk drive. Another method from a magazine involved constructing a chimney to fit over the top vent of the 1541, and that would help draft air out of the drive. Several years ago I received a couple of external disk drive fan units. Though meant for Apple II's, they could be easily modded and placed on top of the upper vent of the 1541 and thus actively draw air out through the top.

Truly,
Robert Bernardo
Fresno Commodore User Group - http://www.dickestel.com/fcug.htm
Southern California Commodore & Amiga Network - http://www.portcommodore.com/sccan
Commodore Los Angeles Super Show - http://www.portcommodore.com/class
 
As an aside, repair tech Ray Carlsen successfully replaced the internal p.s. of a 1541 with that of a modern p.s.. Now the 1541 runs much cooler!
Did this many years ago with the 1541 I'm actually using as well. Very easy and cheap to do.
 

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