Logic Board - Macintosh SE Reloaded

[retr01]

Instead of limiting to "SE" or "SE/30", could you phrase something like "Awesome Tinkering Team Member" that would cover various tinkering? Then a choice of logos for Apple, Amiga, Commodore, Atari, etc.?

It also could be a t-shirt with that Tinkering logo with those words all enlarged on the chest. Proceeds could help to keep this site running and other related things.

Maybe this subject needs to be a new thread somewhere so others can join in and discuss it rather than hijacking this thread?

 

[JDW]

I finally got the rusted metal bar desoldered. Here's the BEFORE photo...



After about 2 hours immersed in CRC Rust Remover (phosphoric acid) -- having removed it a couple times to rub it with steel wool -- I washed it off with water and baking powder (to ensure the acid was neutralized), and then I spend 20 minutes last night and another 30 minutes today scrubing it with fine steel wool. Here's the AFTER pic...



My friend, @Kay K.M.Mods, recommended I also use fine sandpaper and a polishing compound, but I am still waiting for that to arrive. I will consider the polishing compound the final stage before I solder it back in.

 

[JDW]

SE Reloaded Part 3 is now Public for your viewing pleasure:

That completes the build.
Please read the text description that I lovingly crafted for you under the video, as it contains a wealth of information. Mouser Cart is in my Parts List.

I wish to humbly thank @Kai Robinson for his ongoing advice and support.

Folks, please know that your purchases of the red-glossy edition SE Reloaded board on MacEffects here supports Kai. You will find the code to get 10% off (for a limited time, courtesy of MacEffects) in my video.

Now, I realize that SE boards can often be found on EBAY for US$140 or so these days. If you buy most of the components like I did, the total cost of them plus the PCB will set you back more than $140 (not to mention the cost of soldering tools). The build will also take many hours of your time. But I suggest you contemplate SE Reloaded more as an amazing project whereby you build the heart and soul of a beloved vintage Mac. Pondering it that way makes it fun and personally fulfilling. And if you happen to be able to save a battery-bombed SE board from the refuse heap too, all the better.

I will commence filming of the Part IV finale (TESTING) after work this evening. That is perhaps the most important video of all as it will show if my many hours of labor actually works. Fingers crossed.

 

[retr01]

I've got the popcorn ready for the SE Reloaded movies!

Cheers!

 

[JDW]

I've got the popcorn ready for the SE Reloaded movies!

Oh drat! Now you've got me hungry for popcorn!

 

[JDW]

Folks, there's a discussion here about Bourns filter replacements, which has expanded to replacements for the metal bracket and for the plastic mounts for the Reset & Programmer's switches here. Please check it.

 

[tmtrains]

How critical is the metal bracket? I understand it's needed to hook up ground, but are there other critical purposes it serves? I ask because rust destroyed the metal bracket I have. About a 1/4 to a 1/3 of it on the power supply side was completely lost to rust / corrosion from the battery leakage.

(Thanks for the pointer to the thread, it's good to know the Bourns filters can be replaced. Also your video series on the SE reloaded has been really informative as I plan to do the same project soon.)

Folks, there's a discussion here about Bourns filter replacements, which has expanded to replacements for the metal bracket and for the plastic mounts for the Reset & Programmer's switches here. Please check it.

 

[JDW]

How critical is the metal bracket?

It comes in contact with the metal chassis and provides a solid chassis ground. It also adds mounting stability to the motherboard, although with the back case on that may not be a major issue.

BTW, if you have a photo of your rust-eaten metal bracket, I'd love to see it.

 

[tmtrains]

It comes in contact with the metal chassis and provides a solid chassis ground. It also adds mounting stability to the motherboard, although with the back case on that may not be a major issue.

BTW, if you have a photo of your rust-eaten metal bracket, I'd love to see it.

Here it is. You can see that it broke behind the SCSI connector.

 

[JDW]

Holy cow! That's a seriously battery-bombed board.

Well, I must say that even though mine wasn't that far gone, such that I was able to remove the rust and continue using it, having a brand new replacement would have saved me hours of time. And for people in your shoes (which no doubt are many in number), having a replacement is essential. But as @alxlab was saying today in his Bourns thread, JLCPCB has a stainless steel 3D printing service that needs only a 3D file, which is pretty amazing to me. And I see that PCBWay offers laser cutting and bending of sheet metal here. There's no way to know how well it would turn out without trying it, but to try it, we would need a 3D file or CAD file of the stock bracket.

 

[retr01]

IMHO, even if cleaned, the main grey stock chassis doesn't look exhilarating. Back in the early 1980s, I am sure Steve Jobs was very disgusted with how the IBM PC looked inside and out, so he wanted everything to look clean and presentable inside and out of the compact Mac. Arthur Rock and John Sculley would not have that. For many people, it was, and still is, the mentality of "who cares what it looks like inside?" Apple needed to cut production costs and did not have the main chassis shiny metal like the HDD or FDD brackets.

I care. Now that needs to spruce up and shine! I wonder if it is cost-effective to print shiny metal chassis and chassis parts than having those professionally cleaned and nickel-plated locally? I know DIY cleaning methods, nickel plating, or air spray painting, but it means more stuff.

 

[JDW]

I wonder if it is cost-effective to print shiny metal chassis and chassis parts than having those professionally cleaned and nickel-plated locally? I know DIY cleaning methods, nickel plating, or air spray painting, but it means more stuff.

@Kay K.M.Mods knows more about that. As I am sure you saw recently in his post here, he has experience in both plating and painting. (Earlier in that thread he shows photos of how neat a black chassis looks too.)

 

[retr01]

It comes in contact with the metal chassis and provides a solid chassis ground. It also adds mounting stability to the motherboard, although with the back case on that may not be a major issue.

Hey, @JDW! Admittedly, I have thought about 3D printing a replacement chassis. However, that is one piece of metal that can be solid ground. So, I wonder about a workaround? What amount of metal for grounding is required?

Cheers,

 

[JDW]

@retr01
The metal chassis of the compact Macs, and the metal bar on the motherboards, provides both mounting stability and ground. Your hands will come in contact with the metal chassis, so ensuring all those metal parts are grounded is needed for safety. It's no different on your car, where the entire body is grounded.

Technically, the motherboard gets grounded with the main wiring harness. The chassis is merely providing another ground.

Interestingly, I have confirmed with Kai's Gerber files and by backlit observation of the logic board that the ground plane is divided into two parts, and the parts are tied together by a single trace on the top side of the board. That single trace is shown in red below...

Gerber view of the same...

I'm not 100% sure why it is designed like that, unless it anticipates a dead short to ground in the chassis or external connectors, such that the trace shown in red above would act as a fuse and blow (split apart) when a short occurs.

 

[retr01]

Yeah, as I think more about that, as long as the compact Mac used the CRT and analog board, it would be better to have metal chassis. The analog board goes out if the CRT is replaced with an LCD. Then, the chassis does not have to be metal. The replacement PSU would be grounded by the ground part of any electrical outlet plug, and thus the compact Mac can also be grounded that way.

Does that sound reasonable?

Cheers,

 

[JDW]

Yes, "chassis" or "metal frame" ground is supposed to be Earth ground, which requires a 3-prong power cord.

Sadly, here in Japan, 3-prong outlets are extremely rare in most homes. It doesn't affect normal operation of the Mac, of course. It just means chassis ground isn't Earth ground.

 

[retr01]

Technically, the motherboard gets grounded with the main wiring harness. I'm not 100% sure why it is designed like that, unless it anticipates a dead short to ground in the chassis or external connectors, such that the trace shown in red above would act as a fuse and blow (split apart) when a short occurs.

That is true. Good circuit board design usually includes a circuit path that acts as a ground with a piece of metal or to a ground layer of the PCB. I guess that has been around for years.

Can someone shed more light on ground circuitry and whether it is necessary to have a metal chassis?

 

[Bolle]

On the SE/30 it's done in a similar fashion. The "analog GND" as it's called on the schematics is connected to the main/digital ground through inductors.

 

[JDW]

On the SE/30 it's done in a similar fashion. The "analog GND" as it's called on the schematics is connected to the main/digital ground through inductors.

Now that I can understand, with the inductors acting as chokes on the ground. But the SE board only has that single trace from what I can see, which is rather odd, don't you think?

 

[JDW]

Separate topic...

I did my first power on test of the SE Reloaded board while filming. To my delight, I got a display, the arrow pointer, the flashing disk icon, and the startup bong. However, the bong is longer than normal as shown in the short video clip below. I've heard a similar long-beep on my SE/30's before when I had accelerators installed, but the SE Reloaded board I'm testing is stock. Curious if it could be something wrong with the SND chip, CPU or something else. You will agree it is a bit odd, right?