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LC/LCII Power Supply Replacements?

DracheMitch

Well-known member
I have an LC and and LCII, and both have dead power supplies. To my understanding, they're known for failing. Has anyone made replacements for these, or can recommend a refurbishing service?
 

cheesestraws

Well-known member
Has anyone made replacements for these ... ?

The nice thing about the LC series, especially the earlier ones, is that they're really not picky at all about power. They need 5 V and 12 V, and not much of either: if you want to do LocalTalk networking, you also need -5 V.

The pinout is here: https://old.pinouts.ru/Power/mac_lc_power_pinout.shtml

The connector you need, if you want to fabricate a new one, is a Molex KK396. Compatible connectors are readily available on eBay.

When I get home (I am away for a few days) I will be able to post information about how I got mine working, if you like. I built mine from DC/DC converters; a good alternative is to get one of those power supply bricks they sell for driving hard discs in an external enclosure, because many of those provide both 5 and 12 V at adequate levels. @joshc I believe has done this and can talk more about it.

The short version is: depending on how comfortable you are with electronics and what it is you actually want, you have a number of options here, don't worry :)
 

DracheMitch

Well-known member
The short version is: depending on how comfortable you are with electronics and what it is you actually want, you have a number of options here, don't worry :)

If it's just making a harness to connect the new supply to the board, I think I can do that. I replaced my MDD power supply with an ATX one that way. I don't mind taking things apart to scavenge parts, either. I have a soldering iron, but I'm 44 and literally never soldered anything. Don't know what my skills would be there, but I do have one of those clamp on magnifying lights...
 

cheesestraws

Well-known member
If it's just making a harness to connect the new supply to the board, I think I can do that. I replaced my MDD power supply with an ATX one that way.

If you have another PSU that will give 5 and 12 V, yep! If you have one that will give you -5, even better. So it depends how pretty you want it to be really! But yes, a small ATX-type supply and a wiring adapter should do you fine.
 

DracheMitch

Well-known member
If you have another PSU that will give 5 and 12 V, yep! If you have one that will give you -5, even better. So it depends how pretty you want it to be really! But yes, a small ATX-type supply and a wiring adapter should do you fine.
I want it to be electrically safe, and I'd like it to be contained inside the LC. That's about all I care about.
 

androda

Well-known member
This is a problem I'm working on. The MacTX_LC was released into the public domain awhile back. It uses one of those picopsu things to replace your original LC through Q605 power supply.

I had a batch of prototype boards made and then realized it's only using the picopsu for 5v rail. My plan is to make something that uses an external 12v power supply and then down-convert that to the necessary 5v and -5v. We've also located the original power connector, so it could be sold as a complete solution requiring no soldering.

Found the regulator chips I want to use, just needs a board design and some testing.
 

aeberbach

Well-known member
I only have the LC475 so I can't measure myself. What are the dimensions of the failing supply? Should be easy to print up a 3D enclosure with power inlet/switch in the right place, and one of the available power supply modules inside. Very likely a modern module will fit with room to spare.
 

joshc

Well-known member
As cheesestraws has said, LCs are easy to power.

I hooked up a very temporary thing which is now my go-to way of testing an LC if the PSU is playing up, but it does require load on it, so I only managed to get this working right with a SCSI drive plugged in (still haven't tried with a SCSI2SD yet).

This is using a 5V/12V adapter:
1625636472920.png

The spec of the adapter is:
  • Input voltage range: AC100-240V.
  • Input voltage frequency: 50-60Hz.
  • Output voltage: 5V-12V
  • Output voltage regulation: 5%.
  • Rated output current: 2A
  • Current output range 0-2A (over 2A the working time of more than 5 minutes).
  • Output ripple & noise: 100mVp-p.
  • Working efficiency: 80-85%.
  • Operating temperature: 0℃ to+50 ℃.
  • Storage temperature -20 ℃ to+85℃
  • Output short circuit protection.
  • Input plug size: AC socket product suffix
Cut off the Molex connector on the end, revealing the wires so I could hook those up for 5V, 12V and ground:

89868D69-377B-4557-BC1D-C2B6A5E65659_1_105_c.jpeg

What this is missing is -5V which is used for serial on the LC. I haven't gotten around to that bit yet, but it's not needed to boot/use the machine as long as you don't care about serial. ATX PSUs don't have -5V so you have to create it yourself.

After that, the next next thing on my list is to replace the innards of the original PSU with a modern equivalent, and hook up something for -5V. The ideal solution here, in my mind, is to have the original PSU case kept as it is, with the rear switch and AC plug socket as they are, but with the power supply board itself replaced and the original wiring loom kept.
 

mg.man

Well-known member
the next next thing on my list is to replace the innards of the original PSU with a modern equivalent
Have you tried "opening up" that external 'brick'? It looks like the innards would fit inside an LC PSU (housing)... you'd then just need to figure out something for -5V... which, I believe, is only needed for LocalTalk?
 

cheesestraws

Well-known member
you'd then just need to figure out something for -5V

There are pre-built modules that will do this. I use an isolated DC/DC converter but I'm sure there are cheaper ways.

which, I believe, is only needed for LocalTalk?

Pedantically, it's used for differential signalling on the serial ports in general. LocalTalk is the only thing I've found that uses it, but I'm not going to rule out some peripheral manufacturer using it too for some high-speed peripheral.
 

cheesestraws

Well-known member
My plan is to make something that uses an external 12v power supply and then down-convert that to the necessary 5v and -5v. We've also located the original power connector, so it could be sold as a complete solution requiring no soldering.

This would be a really nice thing to have available.
 

adzq88

New member
I was also asking for this kind of a replacement PSU before here, but my messages got lost in the great crash of this forum. I wonder if someone would be able to sell this kind of PSU replacement in the EU?
 

cheesestraws

Well-known member
I was also asking for this kind of a replacement PSU before here, but my messages got lost in the great crash of this forum. I wonder if someone would be able to sell this kind of PSU replacement in the EU?

FWIW, both joshc and I are in the UK, so the "brick" PSUs are certainly available internationally, as are several options to generate your -5 V. If you're meaning more androda's specific plan, I can't speak for that of course :).
 

androda

Well-known member
I'm going to make these in an RoHS compliant manner, so theoretically could ship internationally.

Started laying out the PCB this morning, not sure how long it'll be until completion because kids and life stuff.
 

reallyrandy

Well-known member
I have 2 LCII's with dead power supplies as well :(
One of them does nothing, the other one displays a blank screen and the speaker hums, no fan or HD activity though.
 

bdurbrow

Well-known member
I'm also cooking up an LC PSU adapter. I'm looking to minimize the number of wiring harnesses that need to be crimped together, however; so I located the Molex part number for a board-mount counterpart to the KK396 connector on the logic board.

Molex 09-48-3076; Mouser 538-09-48-3076. As of tonight, they had 827 in stock for $1.47 qty 1.

I'm also going to put pads on the PCB for a MornSun b1205s-1w DC-DC converter, wired to provide -5v.
 

bdurbrow

Well-known member
Well, here's a preliminary board layout. It accepts either a 4-pin disc drive power supply or an ATX power supply (a PicoPSU or an external full-size ATX boxed power supply); and has pads on it for a MornSun isolated DC-DC converter wired up to produce -5v for the serial chips.

I don't have the silkscreen done yet, and (obviously) it hasn't been built & tested yet.

I'm also going to be cooking up similar adapter boards for the SE & SE/30, the Classic (I and II - and yes, their pinout is different from the SE, despite being the same connector), the compact II series (cx, ci, si, and Quadra 700); and the original II series (II, IIx, IIfx). Aside from the SE & SE/30 however, I have no means of testing these; because I don't have these machines in my possession (if anybody wants to donate a logic board - or even a full machine - to the cause, I would most graciously accept it! ;) ).

Lower.pngUpper.png


Screen Shot 2021-08-04 at 6.14.25 PM.png
 

bdurbrow

Well-known member
I think this is ready to go to PCB manufacturing...

Actually, I think I'll add pads for a DPDT switch, so if you are using the 4-pin molex supply instead of the ATX supply you can turn it off without having to unplug the power brick.

Screen Shot 2021-08-11 at 9.32.36 PM.jpg
 
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