Possibility of complete redesign and modern manufacture of LC-LC475 power supplies

[Androda]

I had no idea that little power supplies like these even existed.
It's under-rated on the 5v line by a bit, but so is my board. And this is all-in-one. Just needs cabling and mounts.

 

[RetroTheory]

Its also universal input so it will work on 110V and 220V.

 

[Androda]

After an incredibly long delay, this project is back underway. I've designed a protection PCB that has fuses and zeners to protect the LC motherboard, and it's on the way from JLC now.

@GeekyBit has designed a very nice 3d printed mount for this setup.

More or less we're waiting for parts to show up to do assembly and testing using the prototype protection board.

Thanks to the component shortage, the power supply we picked is in very short supply unless you order from China. So we could place a big order for them, but they're not exactly cheap.

The project is still moving along, but a bit slowly.

 

[GeekyBit]

Here is some early examples of the 3d printed case

 

[GeekyBit]

That's amazing! I need 50 of those please!

well we will be selling them soon sorry there isn't a better Time frame other than soon TM... The fact is this has been an on going project and it was mainly @Androda working on it by himself. We had just talked about some stuff with it. But I have helped out a bit more recently all the PCB stuff is still @Androda , but I have been helping with a lot of the other stuff for this project. IF all goes well there will be other PSUs to fallow.

 

[MacKilRoy]

well we will be selling them soon sorry there isn't a better Time frame other than soon TM... The fact is this has been an on going project and it was mainly @Androda working on it by himself. We had just talked about some stuff with it. But I have helped out a bit more recently all the PCB stuff is still @Androda , but I have been helping with a lot of the other stuff for this project. IF all goes well there will be other PSUs to fallow.

My guess is, if it fits inside the LC power supply housing, it shouldn't be much of a challenge to make it fit inside a IIci style PSU housing. Or is this unit underpowered for use in a IIci?

 

[Androda]

My guess is, if it fits inside the LC power supply housing, it shouldn't be much of a challenge to make it fit inside a IIci style PSU housing. Or is this unit underpowered for use in a IIci?

This particular power supply is too weak for the IIci and similar. Another design would have to be sourced and designed around. I'm sure they exist.

 

[Androda]

That's amazing! I need 50 of those please!

If all goes well with the PCB testing, I could have 5 ready after Christmas.

If you really want to do a large order then let's DM about it. The parts are starting to be in short supply (sigh, like everything else) and might need to be ordered in bulk from China.

 

[Androda]

well we will be selling them soon sorry there isn't a better Time frame other than soon TM... The fact is this has been an on going project and it was mainly @Androda working on it by himself. We had just talked about some stuff with it. But I have helped out a bit more recently all the PCB stuff is still @Androda , but I have been helping with a lot of the other stuff for this project. IF all goes well there will be other PSUs to fallow.

Don't discount your work here, that mount design is miles better than the one I came up with. And you helped scouting for other parts.

 

[Androda]

This is great news. My question on the project is, how do we get a switch and AC power connector on it? Or is that taken from an existing unit?

Can it fit inside a standard LC PSU housing or does it need the 3D printed case you demonstrate?

I’d like a much simpler solution of integrating brand new PSU as like you have there.

This solution doesn't technically need anything at all from the original power supply. Not the case, not the PSU to motherboard cable, nothing.

The new power supply doesn't really fit in the original supply casing, tolerances are just not large enough for it to be safe. Hence the printed bracket.

My intention is to offer probably two different options, with others available on request.

1. A literal drop-in replacement. Power plug and switch preinstalled, all assembled and tested and ready. Pull out old supply, put in new one, done. Downside: Plug and switch are not beige. Current parts on order are black, beige ones are harder to come by.
2. SMD parts preassembled (there are a few SMD zeners on the protection board), with all the remaining parts loose. Power plug and switch not installed, have to solder the rest of the parts together, etc. Includes the mounting bracket, of course.

The "protection board" I mention is basically an over-voltage zener clamp on every rail (12, 5, -5), plus cartridge fuses for 5 and 12. This way (for example) if the PSU has a regulation failure and sends 12v to the 5v line "pop goes the weasel" and the zener + fuse will clamp and pop and protect the board. -5 gets a polyfuse because cartridge fuses rated that low are actually kind of expensive.

I would do a similar protection board on any future PSU designs too.

 

[Androda]

Ok. I’d love to see a picture of the complete “product”. I don’t think switch or socket color really matters much.

Would it be advisable to 3D print a cover for the case so the PSU is shielded from accidental touch?

When I say I could use 50 of these, I’m completely serious. However, that is entirely based upon price. I’m an very willing to solder myself if it saves money. Including SMD (I easily hand solder SMD 1mm in size, like this).

Will definitely post a picture here once I have one fully assembled and tested.

There's not a lot of accidental contact surface on the top of these power supplies, which is pretty surprising. The exposed capacitor top doesn't test as connected to either positive or negative, and most of the rest of the contact surfaces are on the bottom.

The SMD soldering will require a heat gun, because the exposed pads on the zeners are inconveniently placed on the bottom instead of the ends. Vishay SMPZ3928B-M3/84A is one of the zeners used.

 

[Kai Robinson]

You could have the SMD soldering done by JLCPCB if you have the BOM and P&P data to hand, then you only need concern yourself with the through hole parts.

 

[Androda]

Did a test on the latest design (using my LC II), and everything seems to be working. At this point the mounting bracket is probably the final target for some tweaks before this is ready to go.

 

[EffingController]

It's so uplifting to read all of these updates. Thanks to the both of you for all of this work! Can't wait to get one of these babies so I can make my nostalgic dreams a reality.

 

[Androda]

Looks like I need to do a small protection PCB revision. My solution for connecting to the selected power supply is to sit down over the output pins and solder in place. That connector footprint was off by a tiny bit and scrapes the side of the mounting bracket. Moved that, rotated a few things a little different so it looks nicer, and will be doing another prototype PCB run soon.

@GeekyBit and I have some plans to improve the mounting bracket, but it'll take awhile for those to bear fruit. The existing mounting bracket will work, it's just a bit thin around the switch and plug positions because of how little vertical space there is, and this caused one of my test brackets to crack between switch and plug. The LC series has a few prongs that stick down around the switch and plug, and those help hold things in.

 

[Melkhior]

My guess is, if it fits inside the LC power supply housing, it shouldn't be much of a challenge to make it fit inside a IIci style PSU housing. Or is this unit underpowered for use in a IIci?

The (shorted) PSU in my (currently dead) IIci is rated at 12A@5V, 1.5A@12V, 1A@-12V plus 5V trickle.
From Mean Well, the RPT-160B seems an excellent match, offering 14A@5V, 5A@12V and 1A@-12V ; they are also smaller than the current PSU so should be able to fit. They are expensive though, I see them at ~75€ in Europe (in stock).

So a similar approach for IIcx/IIci/IIvi/IIvx/<other compatible> could work to create replacement PSUs.

Edit: PPT-125B could work as well (11.5/3/0.5; -12V probably doesn't matter as a lot of it is provisioned for the NuBus cards and most probably won't use -12V).

 

[Ron's Computer Videos]

Something that utilized the PicoATX would be interesting.

 

[GeekyBit]

Something that utilized the PicoATX would be interesting.

oddly enough that is what this IDEA was born from... however they are way to cost prohibitive, and really they provide a lot of stuff LC doesn't need power wise. @Androda could answer these questions far better than I can since he is the main guy on this. But the PicoATX is a good idea it just isn't practical from what I understand.

 

[Androda]

The origin of this project was the mAcTX_LC which was released into the public domain on 68kmla. I downloaded the files and made one, but was frustrated that the use of a picopsu wasn't enough by itself, because the picopsu doesn't provide -5v. These files were lost in one of 68kmla's many data loss incidents.

So my first revision used a simple 12v power supply with discrete converters for 5v and -5v. This passed testing and works in my LC series machines (LC II, LC III). It's hard to assemble due to the size constraints, though I could revisit it and possibly rework to something better now that I know the available physical space.

Then along came this thread and we discovered that power supplies exist which already provide 12v, 5v, and -5v in the amp capacities we need. These power supplies are cheaper than the picopsu as @GeekyBit mentions. In this particular case it makes more sense to go with this power supply plus a fuse / zener clamp protection board.

Really the project is practically done, all that remains is the mounting bracket. It likes to crack around the power input plug and switch because there's not much vertical space available. There are some little hold-down prongs in this area at the back, which helps in the situation that the mounting bracket does crack. Would be nice to have a metal back plate to avoid the cracking.

Here's a picture of a test fit that I did on my LC II using spade connectors to power plug and switch. Hard soldering seems like the better idea here, given how much space the spades take up.

 

[Melkhior]

These files were lost in one of 68kmla's many data loss incidents.

FYI, they were reposted: https://68kmla.org/bb/index.php?threads/mactx-lc-boards.38912/.