2025 Exxos PSU in 520STE – clearance / case won’t close properly

[mascis]

Hi, I’m hoping someone can advise before I undo all the work I’ve done installing this.

I’ve fitted the 2025 Exxos replacement PSU to my Atari 520STE, along with the recommended replacement power switch. The PSU bolts perfectly onto the original metal base using the existing mounting holes, and I’ve completed the wiring and continuity checks successfully.

Unfortunately I’ve hit a physical clearance problem.

The original PSU shielding plate is extremely difficult to fit over the new PSU. I managed to get it on by carefully routing and cable-tying the wiring out of the way, but even then the Atari’s plastic top case no longer sits naturally. It noticeably rests on/pushes against something underneath and would have to be pressed down while tightening the case screws, which I really don’t want to do.

I’ve also tried it without the PSU top shield, but with the rear shielding arrangement in my particular STE there still seems to be too much obstruction for the plastic case to fit as it originally did.

Is this expected with the 2025 PSU in some 520STE chassis/shielding revisions, or am I missing a particular way this is supposed to be mounted or routed?

I really don’t want to force the case closed or modify the original Atari if that isn’t intended.

Thanks very much for any advice.

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[exxos]

Looking at your last image it looks like the rear IO shield isn't fitted properly.

[mascis]

Looking at your last image it looks like the rear IO shield isn't fitted properly.

Sorry, I should have labelled the photos clearly.

This is how the plastic top case fits on top when I have the PSU shielding plate fitted. It almost fits but not quite. See below:

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And this next photo shows that if I remove the PSU shielding plate and try fitting the plastic top case, then not only am I still battling with the PSU height and getting the wires to lie out of the way but the rear IO shield tab then creates a new obstruction because there is no PSU shielding plate for it to screw into, which would bring it away from the casing and out of the way. See below:

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I'm considering trying to remove that rear IO shielding tab. However I'm not entirely sure how it comes off, but I'm pretty sure I'll have to remove and disconnect the main PCB entirely again to do it, and even then I'm not confident it would give me the clearance that it needs, so I'm not in a rush to do that right now.

[atarifreakz]

you need to fit the 3 black screws that hold the IO shield to the rear of the PSU metal top, If you don't the IO metal sticks out and stops the plastic lid fitting on

From your other pic the PSU metal top looks like it fits on ok so i see no other reason why the plastic lid wouldn't fit

To prove it get a cocktail stick or similar and push the metal plate back and see if the plastic lids fits then

[mascis]

To prove it get a cocktail stick or similar and push the metal plate back and see if the plastic lids fits then

Ah, thanks for the tip about the cocktail sticks! I just got my wife to help provide an extra hand by keeping that IO shield tab out of the way by using two cocktail sticks while I guided the plastic top cover on while making sure all the PSU wires stay as low as possible.

Unfortunately, as I suspected, there still isn't enough clearance even with the main PSU shielding plate removed and making sure that IO shielding tab is out of the way. The new PSU still seems to be obstructing the top cover. To make it fit like this I'd need to compress the wires on top and bend the plastic top cover over them whilst screwing in the from the bottom. Which I don't really want to do, it seems to almost fit, but sadly doesn't.

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[exxos]

Maybe this will give you some clues
https://www.exxosforum.co.uk/atari/last/stedis/main.htm

[Steve]

As long as the PSU top shield fits properly that means the PSU isn't too tall. If the PSU top shield couldn't be fitted at all, that's when you'd know the PSU is too tall. So I am of the same thinking of the other guys, that rear shield is catching on the case. Either that or the entire motherboard has been lifted ever so slightly?

[PhilC]

Just a quick suggestion, have you checked that the mounting bracket is not bent and that it's located correctly in the motherboard slots?

[rubber_jonnie]

I agree with @PhilC, if the metal plate isn't correctly fitted the tabs sit on top of the mainboard and not in their slots and will lift it up by a surprising amount:

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These are the tabs I mean and they are only at the back of the bracket.

Looking at the position of the IEC power socket on your machine I think it's too high as it's touching the top of the case hole. It should be more centrally located.

Also your power switch is touching the top of it's slot in the case, thats too high as well.

Tabs not in the slots will cause this for both the power connector and the switch..

[mascis]

Thanks everyone! I really appreciate the suggestions. They gave me a bit of hope that I’d simply got something seated incorrectly, so I’ve gone back through the machine quite thoroughly this evening to check.

As long as the PSU top shield fits properly that means the PSU isn't too tall.

I think this is probably the main thing I haven’t explained clearly enough: the PSU top shield doesn’t actually fit properly over the new PSU.

I can get the screws into it, but only by using the screws to pull the shield down over the PSU. In doing that, the top of the metal shield is visibly flexing/bulging because something underneath is pushing against it. I’d originally done this partly as a rather inelegant way of clamping the top PSU wiring down as low as possible, but it definitely isn’t sitting naturally in the position the original shield did.

I’ll attach another photo showing the PSU shield simply resting over the new PSU without the screws fitted. You can clearly see that the lower edge is raised rather than sitting down where it should. The only way I can make it meet the mounting points is by screwing it down and flexing the shield. See below:

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When the PSU shield is screwed down, the rear I/O shield tab isn’t the thing stopping the plastic case from fitting, the three black rear screws pull that into the correct position as they should. Even then, though, the plastic top still won’t sit naturally because the PSU/shield area is simply too high.

Just a quick suggestion, have you checked that the mounting bracket is not bent and that it's located correctly in the motherboard slots?

I agree with @PhilC, if the metal plate isn't correctly fitted the tabs sit on top of the mainboard and not in their slots and will lift it up by a surprising amount:

Thanks for this suggestion and the posting a photo. I really hoped this might be it!

Unfortunately I’ve now removed and refitted the PSU mounting plate specifically to check those tabs. Both rear tabs are definitely located in their motherboard slots properly and won’t go any further down. The lower mounting tabs are also screwed down fully, as are the four screws mounting the new PSU PCB to the original PSU plate. I can’t see anything trapped between the PSU and its mounting plate, and there doesn’t appear to be anything there that should have been removed.

I also took the entire motherboard/chassis assembly back out of the plastic bottom case and checked underneath it carefully. There’s nothing trapped under the motherboard/lower shielding, and nothing in the bottom plastic shell preventing it from seating. I tried refitting the assembly at slightly different angles and making sure it was pushed down as far as possible, but it always positively locates back into exactly the same position. I can’t get the motherboard assembly any lower.

Looking at the position of the IEC power socket on your machine I think it's too high as it's touching the top of the case hole. It should be more centrally located.

Also your power switch is touching the top of it's slot in the case, thats too high as well.

Thanks for pointing this out, I agree, the IEC and power switch do look a little high in the rear openings.

However, that position seems largely dictated by the original metalwork: there’s an awkward screw at the rear which fastens the PSU mounting plate to the main shielding and rear I/O shielding, so those parts all have to line up in that position.

I also checked some photos from when I originally received the machine, before I had dismantled anything, and the IEC socket already sat slightly high in its opening then. The other rear I/O sockets look normally positioned within their openings as far as I can tell, so I'm somewhat doubtful that the entire motherboard and the attached PSU base plate is currently sitting unusually high.

Even if I somehow gained another 1–2 mm there, I’m doubtful it would solve the PSU clearance issue. Judging by how far the PSU shield sits proud when simply rested over the new PSU, I’d estimate I need something more like 5 mm or more before everything would sit naturally without being compressed.

So at the moment I’m struggling to find anything else that can physically be seated lower. I’m very happy to check anything specific that I’ve missed, but I don’t want to force the metal shield or plastic case down under permanent tension just to make it close.

Thanks again for taking the time to help, it’s very much appreciated.