running without a fan- Mac SE FDHD

[Mac128]

The Mac mini's case has very little ventilation to start with, and with all the components close together, it certainly doesn't aid airflow. If you did that, you might find cooling becomes less of a problem.

I'm not sure this is the best solution, especially with modern Macs. Even with the Mac 128K Apple was installing heat sinks to help pull heat away from the delicate electronics and radiate it into the case where convective air would then exhaust it. The Apple III itself was inside a giant heat sink which actually kept it cool despite being much maligned as the cause of its failure. This is why I think the PSU in the SE actually runs cooler than the exposed components on the original analogue boards. Notice even the flyback transformer in the SE is surrounded by a heat sink as well.

The Mac mini, being derived from PowerBook technology is designed to rely on sophisticated heat sinks to cool it. My MacBook fan hardly ever comes on unless I'm doing something processor intensive. Take that delicate balance apart and air may not cool it as effectively. Certain components may actually get hotter once contact with the heat sink is removed – and ultimately it's the component we're worried about.

The real problem is inside the SE case. Essentially he has created an environment which may be outside the mini's specs. Apple says the highest operating temperature is 95 degrees (f). This means that if you use the mini in the middle of the Iraqi desert on a table in the sun, even if you hang all the parts on a string dangling in the hot desert wind, it's still operating outside of Apple's specified tolerances. So no matter how much air he has moving around the individual parts of the mini, if the temperature inside the SE case is above 95 degrees, then he's risking failure. In fact, while Apple may rate the mini for use at 95 degrees, I would be surprised if they ever expected it to be used continuously at that temperature. Doing so can only shorten its life versus running it at standard room temperature of 72 degrees. And, the mini runs significantly hotter than the SE, meaning the inside of that case is going to reach 95 degrees much faster than it would with just the SE hardware (and the SE was rated at 104 degrees!).

So I'm back to, he should probably put a fan in the case, even if it's temperature controlled – set to 90 degrees to automatically come on. So a silent fan that only comes on when it has to would not be bad at all.

 

[joshc]

Even with the Mac 128K Apple was installing heat sinks to help pull heat away from the delicate electronics and radiate it into the case where convective air would then exhaust it. The Apple III itself was inside a giant heat sink which actually kept it cool despite being much maligned as the cause of its failure. This is why I think the PSU in the SE actually runs cooler than the exposed components on the original analogue boards. Notice even the flyback transformer in the SE is surrounded by a heat sink as well.

I doubt very much that a single thin piece of metal can absorb and dissipate heat in any meaningful way to actually maintain or reduce temperatures. A good heatsink that actually does its job usually has some form of extruded cross section.Larry Pina's Macintosh Repair & Upgrade Secrets book mentions that the SE's flyback transformer is surrounded by a high voltage shield - not a heatsink. Do you have something to confirm that the SE's PSU runs cooler than the exposed PSU on earlier analog boards? Though I haven't done extensive tests in this area, logic would suggest that the high number of closely positioned capacitors would restrict airflow (even with a fan), therefore contributing to an overall rise in temperature in the enclosed PSU. This is in contrast to the earlier analog boards where the components have a bit more room to "breathe". Also I would think they placed the PSU inside its own case in the SE for safety reasons - those large capacitors hold a dangerous charge, even after a unit has been powered down. This would make sense, as the SE was the first compact mac to include a flyback transformer with a built-in bleeder resistor, another safety precaution that previous Macs didn't have.

 

[Mac128]

I doubt very much that a single thin piece of metal can absorb and dissipate heat in any meaningful way to actually maintain or reduce temperatures. Larry Pina's Macintosh Repair & Upgrade Secrets book mentions that the SE's flyback transformer is surrounded by a high voltage shield - not a heatsink.

Actually I made an assumption about the metal cage around the flyback being a heat sink, just as you have about other things. Thanks for correcting me on that. However, Pina also refers to a known heat sink removed from the top of early Compact analogue boards as an RFI shield, so I'm not convinced his reference is concrete proof the cage only served one purpose. As for thin piece of metal being a heatsink, the compact Macs are full of them. Take a look through Pina's book, there are a number of individual components that are attached to "irreplaceable" heatsink fins, which are no more than thin sheets of metal (in particular the Q3). I would argue your "extruded metal" sink is based on your modern understanding of a heat sink, as well as assuming the same is necessary for lower temperatures and higher tolerances of capacitors vs. CPUs. As I already pointed out, the PSU inside the HD20/SC is entirely enclosed in a metal box with no air circulation. It must be relying on a conductive heat sink to cool the internal components as that is the only surface exposed to the airflow.

Do you have something to confirm that the SE's PSU runs cooler than the exposed PSU on earlier analog boards? logic would suggest that the high number of closely positioned capacitors would restrict airflow (even with a fan), therefore contributing to an overall rise in temperature in the enclosed PSU. Also I would think they placed the PSU inside its own case in the SE for safety reasons. This would make sense, as the SE was the first compact mac to include a flyback transformer with a built-in bleeder resistor, another safety precaution that previous Macs didn't have.

Again, I make an assumption which has not been tested. This is based on Pina's observations that the various components have a higher tolerances and therefore are not being routinely operated close to their ratings, thereby running cooler. However, Larry Pina's Macintosh Classic and SE Repair and Upgrade Secrets specifically refers to the "heat sink screw" at the front of the PSU and makes specific mention of heat sink grease if the internal insulator falls off. So clearly some aspect of the cage, if not all of it is acting as a heat sink for Pina to refer to it as such. With the Astec PSU he specifically references a heat sink as part of the assembly, as well as with the Sony hybrid PSU. In neither Book does he mention safety concerns when handling the PSU, whereas he specifically mentions discharging the bleeder-type resistor flyback "just to be safe". Also, I've never seen a reference to safety regarding dealing with the older exposed PSUs in any official publication. As for the "safer" flyback transformer being introduced with the SE, I'm not sure that was an effort only to make it safer, particularly since Pina and Apple both continued to recommend discharging them. I am also not sure it was introduced specifically for the SE which did not occur until 16 months after the first Pluses shipped. I would suggest it was simply a more robust flyback which Apple realized for some time it needed to adopt, but didn't want to pay for it. There was already a revision (if not two) to the Plus analogue board coinciding with the Platinum Plus in January 1987, perhaps to accommodate the new flyback. In any event I speculate the bleeder-type was simply a by-product of the transformer manufacturer's own innovations.

But all of this is conjecture without knowing the Apple engineer's actual rationale and doing some testing towards using the SE in a manner inconsistent with its engineering.

 

[joshc]

However, Larry Pina's Macintosh Classic and SE Repair and Upgrade Secrets specifically refers to the "heat sink screw" at the front of the PSU and makes specific mention of heat sink grease if the internal insulator falls off.

This would explain the grease and what would seem to be a thermal pad that lie between the cover of the SE's PSU, and the two transformers inside the unit. I discovered the same sort of grease inside the PSU from an LC III (I think it was a TDK).

But all of this is conjecture without knowing the Apple engineer's actual rationale and doing some testing towards using the SE in a manner inconsistent with its engineering.

Makes you wonder where these people got to - surely they have Internet access and would have found the forums at one time or another. Oh well.

 

[LCGuy]

Knowing (cr)Apple they're probably still bound to an NDA and can't say anything. I know these machines are 22 years old, but still....Apple is Apple, and we all know what they're like.

There's also the chance that they may simply have moved on to bigger and better projects and forgotten about it.

 

[superpantoufle]

Sorry for having letting you guys down a couple of days…

I won't rework on my Macminitosh for now. Whenever I find some time to play with my collection as of late, my main goal is to teach myself enough soldering skills in order to do some recapping job. Scoop: one of my LCIII is running just fine for the last two hours, with brand new caps. And the annoying whinning sound that came from the speaker from time to time seems to be gone for good! I'm quite proud of myself, since that was the first time I ever touched a soldering iron.

Now, back to the Macminitosh and airflow inside a SE case: Mac128 is right about mounting the Mini's elements open in the SE case not being a good solution. The Mini's inside is well designed, so the airflow passes everywere to cool everything. Basically, running it open just breaks the airflow. At first, I ran it without its cover inside the SE case, thinking it would somehow cool it. But I quickly noticed the fan would be pretty much always on. Now, with the cover on, the fan only starts up after about one hour, or when the Mini's on a processor intensive task.

As of the Mini running outside of Apple's specs, you're most certainly right. I never put a thermometer inside the case, but it does feel pretty hot in there. Certainly around 100º F. So as I said before, my best solution would certainly to put a big silent fan inside the case. Maybe I'll do it, someday!