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

[Mr. Fahrenheit]

How difficult and how impossible would it be to design a brand new LC-class power supply, to fit inside the original metal PSU case, but with an open source PCB and available parts from Digikey? With all of the modern recreations of RAM, VRAM, logic boards, etc., I can't imagine this would be impossible.

 

[Androda]

I'm working on something along these lines, called the 'MACAA'.
Uses an off the shelf MeanWell 12V power supply plus custom 5v and -5v converter board. These plus 3d printed mounting solution and either reuse the old connector or newly made connector (because the shell and contacts are still available). And it looks like it's all going to fit within the footprint of the original power supply.

I currently have (what I hope is) the final prototype PCB for the converter board (gone through three revisions tweaking stuff), just need to set it all up and try longer term use in my LC III. And the mounting bracket needs a redesign, it's pretty ugly.

 

[Ron's Computer Videos]

Another easy solution would likely be an adaptor that has the LC-class power supply power interconnect header on one end and terminate at a female ATX socket. Then a solution like the picoPSU could be plugged into that.

I don't think this would address the -5V being absent, but isn't that use for certain serial devices?

 

[Androda]

There was a project doing exactly that called the mAcTX LC. They released the PCB design as 'public domain' back before the latest 68kMLA data loss incident. I didn't like that approach (PCB design junkie) and went through the process of making my own.

The MACAA will be compatible with direct-wiring to a 12v supply (like the meanwell unit I mention) or also takes a standard 12v barrel jack supply if that's all you have.

 

[Androda]

Could your design be modified to also work with other Macs? Like the IIci style PSU?

Unfortunately it's not quite that simple. The LC PSU is 0.75 amps at 12 volts and 3.75 amps at 5 volts (with a tiny -5v supply for Serial or someting). Not really a lot of power going on here.

IIci and similar have more along the lines of 12 amps output at 5 volts. Q900 has something absurd like 30 amps at 5 volts and another 15 or 20 at 3.3 volts. The chips I chose for this LC design simply don't have the grunt to do that sort of thing. Chips and designs which *can* handle that kind of power do exist and are possible.

I have no doubt that with a suitably-sized 12 volt primary supply, something similar could be created for other Macs. Main questions are whether a 12v + down-converter style makes sense in each case. I'm sure there are some machines where an ATX plus adapter board would work much better.

 

[Kay K.M.Mods]

I made it a while ago. I'm glad if you can use it as a reference.
See the details of my post:

https://tinkerdifferent.com/threads/lc475-with-kei-truck-style-monitor.52/

And my blog:

『Mac LC475 restore, PSU build and Overclocking』

*Jun 21, 2021 Added few schematics and descriptions. I recently repaired my fri…

ameblo.jp

*The screen doesn't appear immediately cause it has 64MB of memory and the checksum takes some time...lol

 

[Mr. Fahrenheit]

This power supply seems readily available and very cheap: https://www.ebay.com/itm/311327132800

The only thing it would be missing is a -5v DC. How difficult would it be to build a PCB with the components needed to also have -5v DC? These could easily be inserted into an existing LC PSU housing, and are very inexpensive. Thoughts?

 

[Kay K.M.Mods]

This power supply seems readily available and very cheap: https://www.ebay.com/itm/311327132800

View attachment 899

The only thing it would be missing is a -5v DC. How difficult would it be to build a PCB with the components needed to also have -5v DC? These could easily be inserted into an existing LC PSU housing, and are very inexpensive. Thoughts?

Unfortunately, this PSU cannot be used.
To know all the currents used for + 12V, + 5V, -5V, refer to the original PSU label.
W= V x A
In the case of LC475, a total PSU of about 45 to 60W is required. *I used 90W...I think it was
Use an inverting regulator to generate -5V.

Furthermore... one thing to keep in mind when using a normal ATX power supply is that a 68K Mac has a much higher current at + 5V than at + 12V.
If you wait for about 12 hours, I will calculate this and reply again.

 

[Kay K.M.Mods]

Genuine PSU specs:
+5V x 4.75A = 23.75W
+12V x 1.0A = 12W
-5V x 0.075A = 0.37W
The wattage for each volt your Mac needs is listed above.

Total wattage : 36.12W *I think actual total wattage is more bigger about 40W or more.
The voltage must be generated at a volt number higher than 12V, when all are controlled by a regulator.

I replaced this with a DELL laptop power supply 20V / 4.5A (90W),
It was controlled by a DC-DC converter (maximum 4A) for + 12V and + 5V,
and a negative voltage inverting converter (maximum 0.4A) to -5V.

If you use a PSU that already has + 12V and + 5V output, + 5V must generate at least 23.75W.

 

[max1zzz]

-5V isn't actually required for the LC series to work, IIRC it is only used for serial
Those ext hdd psu bricks do work fine (I have seen a couple of people use them) but I would worry about them being a little on the under powered side if you have spinning disks or PDS cards installed

 

[Kay K.M.Mods]

-5V isn't actually required for the LC series to work, IIRC it is only used for serial
Those ext hdd psu bricks do work fine (I have seen a couple of people use them) but I would worry about them being a little on the under powered side if you have spinning disks or PDS cards installed

Oh I didn't know -5V unplugged and boot, Can it certainly boot on the LC475?
If that is true, you have to apologize for the wrong information point

However, when I checked the wattage of the small AC-DC adapter (same as Mr.F's link) I had, it was 32W, which is not enough for the rating. Moreover, 5V has only 2A output.

 

[max1zzz]

Oh I didn't know -5V unplugged and boot, Can it certainly boot on the LC475?
If that is true, you have to apologize for the wrong information point

However, when I checked the wattage of the small AC-DC adapter (same as Mr.F's link) I had, it was 32W, which is not enough for the rating. Moreover, 5V has only 2A output.

I have to confess I'm not 100% sure there, I was testing it on a LCIII when I did my test's, I would expect the 45 would be the same but I haven't personally tested it.

Yeah it's proabley enough for a LCI with a SCSI2SD, but your crazy souped up LC475 might require a tad more juice than one of those bricks can provide

 

[Kay K.M.Mods]

I have to confess I'm not 100% sure there, I was testing it on a LCIII when I did my test's, I would expect the 45 would be the same but I haven't personally tested it.

Yeah it's proabley enough for a LCI with a SCSI2SD, but your crazy souped up LC475 might require a tad more juice than one of those bricks can provide

I saw the first post again, but Mr. F said that it was the PSU for the LC series, but not the LC475 I may not have followed the topic

I don't have a Mac up to LCIII, so I can't actually verify it...
But I think all 040 machines need -5V if Mr.F had a LC475(?). I add that all my test results are by my hands and I haven't got the wrong results on my machine.

Amazon.com

Btw, this is the DC-DC converter I used. You can use it with confidence because it produces a maximum of 5A.

 

[Mr. Fahrenheit]

I saw the first post again, but Mr. F said that it was the PSU for the LC series, but not the LC475 I may not have followed the topic

I don't have a Mac up to LCIII, so I can't actually verify it...
But I think all 040 machines need -5V if Mr.F had a LC475(?). I add that all my test results are by my hands and I haven't got the wrong results on my machine.

Amazon.com

Btw, this is the DC-DC converter I used. You can use it with confidence because it produces a maximum of 5A.

The topic was for replacement power supplies for all of LC, LC2, LC3, LC475. I have a large number of these Macs (well over 50!) and almost all of them need a new or recapped power supply.

My thoughts are a lot of people are in the same situation as me, fully recapped and working logic boards but no way to use them because PSU has died.

Can it not be easily done where a PCB is designed and parts from digikey ordered and a user just solders them together and now you have a good, new working power supply?

I’m not an engineer or have knowledge of the designs of these things but I just can’t imagine that it would be very difficult to design a power supply, if someone knows what they are doing.

And if a PSU could be designed, perhaps slightly modified to also work in the IIcx/IIci/Q700/Q650/etc series.

Building a power supply from another power supply seems to easier route, but it relies upon obtaining the PSU to be modified. Building one (if possible) involves ordering a PCB and components and soldering them. That’s what I’d like to see.

 

[Androda]

Been a long time since any updates, sorry. I'm sending a pcb and parts to @GeekyBit so he can put together a better mounting bracket than I designed.

The PCB accepts a 12v power supply with barrel jack, or direct wiring into a 12v supply. There's no switch on the PCB, so your external 12v supply is in charge of switching on / off. Tested it on my LCIII, boots right up.

Only additional testing is to try an Ethernet pds card and original hard drive (was using bluescsi of course).

 

[Androda]

Will this provide enough amperage for use in an LC475? I’m very interested!

The 5v regulator is rated at 4.25 amps, slightly less than the 4.75 which the original power supply is rated for.

It can briefly push 6 amps (this is the peak current limit), and if a small/quiet fan is integrated then 4.75 amps is probably doable. Just needs a fuse rated that high, currently testing with a 4 amp fuse.

My Q605 currently doesn't boot (chimes of death) or I'd test it. Use of a bluescsi as hard drive would probably cut 5v power draw by around the 500mA difference between this one's capacity and the original.

 

[GeekyBit]

Will this provide enough amperage for use in an LC475? I’m very interested!

In theory yes. Given the LC475's power requirements, but if you have a lot of extras in there you might run into some issues. Keep in mind the system doesn't actually draw a lot of power, however with say a CPU upgrade, Add in card, and a High RPM old hard drive... you might push some limits.

 

[reallyrandy]

I would love to have some replacements for my two dead LCII PSUs (1 Astec, 1 TDK). I got the re-cap kits but haven't gotten around to recapping. I don't even know if recapping will fix them.

 

[GeekyBit]

I would love to have some replacements for my two dead LCII PSUs (1 Astec, 1 TDK). I got the re-cap kits but haven't gotten around to recapping. I don't even know if recapping will fix them.

Most the time it will ... and the other parts aren't hard to fix either... Just some times they are hard to source. The good news is once @Androda has his solution done there will be a way to get those... In working with him one thing I have found out is the LC PSU will work on a IIGS ... so with a larger 3d printed housing it might work in a IIGS too.

 

[RetroTheory]

Just a size reference on the meanwell rpt 60b , but rpt-60a might be better as it has -5V, 5V and 12V