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Rebuilding The Power Supply With Modern ATX Innards - IBM 5162 “XT 286” Restoration


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In this episode of my long running IBM 5162 “XT 286” restoration and upgrade series, I transplant a modern ATX power supply into the original PSU casing, retaining the original looks and - most importantly - that lovely chunky power switch.


Welcome to part 4 of my ongoing IBM 5162 restoration and upgrade series! This interesting and now very rare PC from 1986 was pretty badly compromised compared to IBM’s other offerings of the time, with some rather cheeky artificial restrictions, which is a story I talked about in part 1 as well as running one of my favourite games of all time - Wolfenstein 3D on it in what would become something of a recurring theme.

In parts 2 and 3 I set about upgrading this machine which is something that IBM very much didn’t want people to do, and I was actually pretty successful despite a few pitfalls along the way. I’ve also given everything a thorough cleaning and replaced the tantalum capacitors to hopefully keep it running for another 35 years.

On that note one thing I really want to address is the power supply. As with most PCs of this era, the original one is inefficient and noisy, and if it had some kind of age-related catastrophic failure it could also have destroyed other bits of rare old hardware in the process.

So let’s get cracking on that, and finally start putting this thing back together for hopefully the last time.

As with all of these jobs, the most important things to me are retaining the looks and functionality of the original, and of course a big part of that in the 5162’s case is that lovely chunky power switch. I did think about maybe using a Mean Well or other high end brand new unit, but to be honest this PC isn’t going to be getting heavy use and this TFX PSU from a modern small form factor PC has proven to be reliable in the few years that I’ve had it. It’s also pretty basic itself so hopefully future maintenance shouldn’t prove to be too much of a problem.

But first we need to get into the original PSU and being rare and vintage IBM hardware there’s sadly only one way to get past these impenetrable security bits.

Wait, no, turns out they’re just Torx bits. Phew! That saved a lot of trouble.

Now, while I like my hardware original, I don’t generally consider the power supply to be part of that and having it not blow up is much more important to me. Of course I’ll be careful to keep the original innards just like I always do with all of my upgrades.

After removing the screws, the back panel of the original PSU locks together with these two metal tabs, and I’ve discovered that a metal scraper is perfect for teasing them apart without bending anything or causing any further damage.

As I mentioned, I want to keep the original power switch which is a pretty iconic feature of these machines, and I don’t want to risk breaking the old plastic tabs by removing it, so although it’s a bit fiddly, I’m going to desolder this in place.

Wow, this is pretty disgusting inside, which is surprising considering how clean the rest of the PC was. I’m guessing it’s probably never been opened up and cleaned.

So after removing the four screws the main PCB is just held in place with a plastic standoff - this very one in fact - and I apparently didn’t record its removal - so, sorry about that.

Then the guts just lift out, revealing even more of that filth underneath. So before I go any further, it seems sensible to blast all of this out with the air compressor.

Here’s that TFX PSU, and there’s no particular rhyme or reason for choosing this one other than the fact that it’s always been very reliable for me and I’ve already used it to run this machine quite happily in previous videos. It also fits very neatly inside the original PSU housing.

Stripping it down, I discover that the PCB is held in place by only two screws - one on each corner - and of course they won’t line up with any of the existing screw holes or mounts so I’ll need to do something about that.

I made a pretty simple paper template so I know where to drill, and it seems the camera cut out at this point but I’m sure you know what drilling holes looks like so we’ll swiftly move on to some soldering.

So just before I test fit this I’m going to remove all of the orange 3.3V wires as they’re not required for a PC of this age, and that also includes the 3.3V sense wire which in a modern ATX system detects the voltage at the load end to compensate for voltage drop, but of course, in this case it’s also surplus to requirements.

A quick test fitting shows that it all fits inside rather neatly, but I don’t want to linger too long admiring it as I still have a fair bit of soldering ahead of me.

Of course the new unit uses an ATX connector which was introduced by Intel in 1995 and is still a de facto standard to this day, but this 1986 PC uses AT, which had only been invented a few years previously by IBM - for this PC’s predecessor the 5150 no less - the very first DOS PC, and a machine that I own and have covered a few times previously on the channel.

I’d been using a simple adapter up until this point, but I’m removing the original wiring and will be grafting it on to the new PSU as it means that all the wires will be the correct lengths and types for this system and will retain the original looks.

I also need a smaller modern floppy power connector for my XT-IDE card which the new PSU already has so I won’t need to use an adapter for that anymore.

Once the wiring loom is removed from the original PSU I can start grafting it on to the new one, and this means going wire by wire splicing and soldering, and adding heat shrink as I go to insulate it all and add some mechanical strength.

The process is pretty fiddly and time consuming but hopefully I’ll only have to do it once so it’s worth spending the time to get it right and keep it all as neat as possible.

There is a wire left over on the AT side which is -5V, which isn’t included in some ATX PSUs - including this one - but we’ve already proven we don’t need this in testing. Just out of interest, it is used for some serial communications cards and soundcards and the like, although the AdLib clone I’m using with this PC is quite happy without it. I ran into this in my previous Point Of Sale PC rebuild project and it didn’t prove to be a problem there either so I’m pretty confident that it’s not going to cause any problems going forward.

Although modern PCs have ACPI and can switch themselves on and off and so don’t tend to use an old fashioned toggle switch for power, this can still actually be wired in to an ATX PSU by grounding pin 14 - usually a green wire - and so that’s what I’m going to do. There’s also another spare ground which - as I’ve used plastic standoffs - I’ll connect to the outer casing to make sure this is all grounded properly.

So first things first, let’s crimp a connector on to that and get it screwed down so everything’s safe. Then it’s just a case of soldering the green “power on” wire and the other spare ground to the power switch.

I’m reusing the original power connectors on the back panel as they’re the standard IEC or “kettle lead” type, along with the original wiring so let’s get that soldered on, and as you can see the new PSU had some decoupling and bypass capacitors on the power input which I’ve already transferred over. They’re probably not strictly necessary but they’ll help to clean up and RF noise so why not.

As the fan was the same size and much quieter than the original I’ve also transferred that over reusing the original screws and already extended the wires, so I’ll crimp some spade connectors onto those to make future disassembly easier, as this top panel comes off separately.

The cables are all bundled up neatly with those soldered joins on the inside to stop them getting pulled about, and passed through to the outside world using the original grommet. So after a thorough test of the fan and the voltages, it’s finally time to put the lid back on.

And there we have it - one fully reassembled power supply, and from the outside you really can’t tell that it’s hiding those modern guts, which is fantastic!

A flick of that amazing chunky toggle switch and I can feel the airflow. This is actually the only fan in the system and helps to ventilate the case too, which probably explains how all of the muck ends up collecting in here.

The cool thing is that the new PSU is dual voltage just like the original so the sticker is still correct, and being 300W compared to the original’s 157W it should have plenty of oomph.

So now it’s time to start putting this old PC back together, and the case is in lovely clean condition with its original cork feet all intact, which is always great to see.

The first thing to go in is that reconditioned PSU, which slots into a couple of tabs on the bottom of the case and also screws in from the back.

Of course a PC isn’t much of a PC without its motherboard, so that goes in next, and as mentioned in the previous video, I’m going to build this up as an 8MHz system for now, so I’ll swap the crystal out for the 16MHz version.

If you want to know a little bit more about how this works and you haven’t seen the previous videos in this series - or need a refresher because it’s been months since the last update - I’ll link the playlist down in the description below.

So now it’s just a case of inserting my XT-IDE, which is an ISA card that allows IDE hard drives to be used with these old systems - in my case, I’m using a Compact Flash card to make life even easier - and the VGA graphics card that I’ve been using for testing in all of my previous videos.

Of course I won’t be using this TFT monitor with this PC longer term but it takes up less space on the desk so it’ll do for now - and it is IBM branded after all. Speaking of IBM hardware, to complete the setup there’s also this lovely Model M keyboard which was very kindly donated by Byron from the channel Has Beard, Plays Games in the previous video. I’ll link to his channel again down below.

So with the patron saint of old PCs himself watching over me, I flick the power switch and…

…it boots!

Running the Check-It benchmark again shows that 37% speed boost over the stock configuration that we saw before, and of course I also have to play some Wolfenstein 3D. Partly as a bit of a burn in test, and partly because it’s tradition at this point, but mainly because I love it and I’ve surely earned it after all that hard work.

So there we go, another bit of future proofing done, and in the next video I’m planning on finishing putting this back together - which as you can see I’ve already started on - and also going over the software setup side of things. I’ve put an Action Rewind card in this system which is a modern clone of the old Action Replay and will allow me to have loads of fun with those old DOS games including cheating by messing around with the memory as they’re running, taking screenshots and some other cool stuff, so you can also look forward to a video on that particular piece of hardware in the near future.

Big thanks to my patrons and channel members as always for your support - you can see their names on screen as I speak - this support helps to make these projects possible and every penny raised and then some is invested directly back into the channel and helps me to justify the time that I spend on it, so it’s genuinely very much appreciated.

Finally, all that’s left is to thank you very much for watching, and I’ll hopefully see you again soon.

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Relevant Links:
Has Beard, Plays Games:
Action Rewind:

Further Viewing:
Point of Sale PC Part 1:
Point of Sale PC Part 2:

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