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Stealth Macintosh IIcx/IIvx style SFX PSU rebuild

demik

Well-known member
Hello,

I've been asked to post this here on IRC so there it is. A lot of PSUs from this era are bad quality and difficult to repair (if possible at all). One of the worsts is the Astec AA15830 (Apple P/ 699-0392)

One of the solution is to use the excellent adapter board by @blusnowkitty and @Compgeke (thread here)

I didn't want to use a full ATX PSU and wanted to keep the plug & play part of the original PSU.
Here is a quick teardown on how to do it:

You need a SFX PSU, a lot of heat shrink tube and an axle grinder or something to cut PSU cases. Here is what you start with:

stealth_PSU_1.jpeg


Next you have to gut the old PSU. Keep the Motherboard and wall connectors with the maximum possible wire length:
Also remove the new PSU board from its enclosure. You need to cut the bottom of the NEW cpu and screw it inside the OLD PSU like this:

stealth_PSU_2.jpeg


Next thing to do is to connect all wires from the new PCB to the old connector. It's helpful to remove unused cables from the new PSU as well.

stealth_PSU_3.jpeg


For the power on circuit, you need to build the same circuit as Eric Bylenga described on his blog
The relevant part is this one:

circuit640bw.jpg


It's easy to do without a PCB, just weld both resistors to the NPN Transistor, head wrap everything and you are good to go.
You can now close everything and nobody can guess what's inside

stealth_PSU_4.jpeg


The old fan is wired to new PCB fan header, so now the fan is temp controlled as a bonus

Hope this is helpful to somebody !
 

jessenator

Well-known member
Nice! Yeah, I'm certain the recapping of the originals is buying only a few more years, perhaps, so it's nice to know there are some drop-in solutions for the original. @Fizzbinn and I were making up re-cap diagrams for this series of (varied designs…) compact-desktop PSUs

Personally, if anything beyond just caps start to go, I'm definitely going to go with your route @demik of dropping in a budget ATX's guts and call it a day. Thanks for that!
 

joshc

Well-known member
@demik This looks great, but I do have one question about the implementation.

How do you deal with the input filtering on the high voltage side if the PSU manufacturer attached components to the AC socket rather than the PCB. Would you move the components over to the socket on the original PSU?

I cannot remember if the original Astec PSU has some filtering components attached on that end already.

Example photo of what I'm talking about, from a Silverstone PSU:

1626422366264.png
 

joshc

Well-known member
The Seasonic I was planning to use for a conversion is even worse, it uses a whole mini PCB on the back of the AC socket which doesn't look like the easiest thing to move across. :unsure: I can see X / Y class caps on that board, which are absent from the Astec housing.

54F44500-0861-4F50-AA70-6764062E9639_1_105_c.jpeg

Astec side:


31199BC7-FB19-4372-9F8F-BC4130876745_1_105_c.jpeg
 

demik

Well-known member
Hello @joshc

Both circuits (SilverStone and Seasonic ones) are passives Power Factor Correction circuits. Long story short, it helps having a better efficiency but isn't part of the PSU per see. It's more off an helper circuit for non linear loads.

PFC is mandatory since 2001 in EU, but even after that, a lot of low quality PSUs were shipped without a PFC circuit. A lot of our old PSUs were shipped without any PFC circuity.

Your PSU will do fine without. It's just better of you can keep it. If not, not a big deal for a vintage equipment which probably didn't come with one.
 
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