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Replacing IIsi Power Supply PSU with a new alternative
Posted by: MrFahrenheit on 2023-03-25 04:37:08
There are a few projects on the go regarding replacing old Mac power supplies (like those in the LC Macs) with new Mean Well power supplies.

This got me thinking: the IIsi PSU needs +5v, +12v, and -12v. The Meanwell RPT-75b seems to be an ideal fit.

From what I’ve found the IIsi needs:
6.8amps for 5 volts, 0.8amps for +12v, 0.3amps for -12v.


Thoughts on whether this would work in a IIsi?
Posted by: cheesestraws on 2023-03-25 04:45:37
I think if I were in your position I'd give it a go, although you'd lose soft power, which would be a bit of a pain.

My only thought is that in the spec, the minimum current draw on the 12V line is given as 0.2A. What I can't tell from the datasheet is whether not meeting the minimum current draw will also affect the 5V and -12V lines' regulation. I'm guessing probably not, meanwell stuff I've had has been better built than that, but be aware it's a possibility that you might need to add a bit of extra load to the 12V and/or -12V line to stabilise things.

Here's the datasheet for the series, which isn't linked from the page you were looking at I think: https://docs.rs-online.com/58ee/0900766b81621f56.pdf
Posted by: MrFahrenheit on 2023-03-25 04:51:51
I think if I were in your position I'd give it a go, although you'd lose soft power, which would be a bit of a pain.

My only thought is that in the spec, the minimum current draw on the 12V line is given as 0.2A. What I can't tell from the datasheet is whether not meeting the minimum current draw will also affect the 5V and -12V lines' regulation. I'm guessing probably not, meanwell stuff I've had has been better built than that, but be aware it's a possibility that you might need to add a bit of extra load to the 12V and/or -12V line to stabilise things.

Here's the datasheet for the series, which isn't linked from the page you were looking at I think: https://docs.rs-online.com/58ee/0900766b81621f56.pdf

Thanks, I might give this a go.

In another related PSU question, the IIci PSU seems to require 15amp +5v, 2.5amp +12v, 0.6amp -12v.

Would the Mean Well RPT-160b work in a IIci, with only 14amps at 5v?

MEAN WELL WEB is officieel distributeur in Nederland en België. MEAN WELL voeding nodig? Wij zijn specialist in AC/DC, DC/DC en DC/AC voedingen, converters en inverters. Bestel direct online je DIN Rail voeding, LED drivers, AC/DC omzetters, DC/AC in

MEAN WELL Web is de officiële distributeur voor Nederland en België. Bestel eenvoudig online AC/DC voedingen, LED drivers, DIN-rail voedingen, DC/DC converters en meer. Specialistisch advies, snelle levering en een compleet assortiment voor industriële en professionele toepassingen.
www.meanwell-web.com www.meanwell-web.com
Posted by: Phipli on 2023-03-25 04:53:03
One other thing, the link you shared quotes the wrong 5V current for that PSU, other sites and the manufacturer quote 6A.

RPT-75-MEAN WELL Switching Power Supply Manufacturer

MEAN WELL is one of the world's few standard power supply mainly professional manufacturers, covering 0.5 to 25,600W products are widely used in industrial control, medical and other fields, in line with international safety certification, short delivery of spot inventory.
www.meanwell.com
Posted by: MrFahrenheit on 2023-03-25 04:56:17
One other thing, the link you shared quotes the wrong 5V current for that PSU, other sites and the manufacturer quote 6A.

RPT-75-MEAN WELL Switching Power Supply Manufacturer

MEAN WELL is one of the world's few standard power supply mainly professional manufacturers, covering 0.5 to 25,600W products are widely used in industrial control, medical and other fields, in line with international safety certification, short delivery of spot inventory.
www.meanwell.com

Ahhh!! There seems to be two specs quoted: “rated current” and “current range”. They are rated for 6amps and range can be Upto 8amps according to specs. Some sites seem to quite the high end of the range as the max. Interesting…

Would that little bit of under value matter at all?
Posted by: Phipli on 2023-03-25 04:56:31
Thanks, I might give this a go.

In another related PSU question, the IIci PSU seems to require 15amp +5v, 2.5amp +12v, 0.6amp -12v.

Would the Mean Well RPT-160b work in a IIci, with only 14amps at 5v?

MEAN WELL WEB is officieel distributeur in Nederland en België. MEAN WELL voeding nodig? Wij zijn specialist in AC/DC, DC/DC en DC/AC voedingen, converters en inverters. Bestel direct online je DIN Rail voeding, LED drivers, AC/DC omzetters, DC/AC in

MEAN WELL Web is de officiële distributeur voor Nederland en België. Bestel eenvoudig online AC/DC voedingen, LED drivers, DIN-rail voedingen, DC/DC converters en meer. Specialistisch advies, snelle levering en een compleet assortiment voor industriële en professionele toepassingen.
www.meanwell-web.com www.meanwell-web.com
I prefer to exceed ratings if possible, but it would work as long as you didn't max out the machine with high current hard disks and high power nubus cards. It's about a 7% shortfall.

The later Centris and PM 7100 PSUs were slightly higher rated than the IIci ones, I'd aim for those ratings so I had a universal solution.
Posted by: MrFahrenheit on 2023-03-25 05:07:01
I prefer to exceed ratings if possible, but it would work as long as you didn't max out the machine with high current hard disks and high power nubus cards. It's about a 7% shortfall.

The later Centris and PM 7100 PSUs were slightly higher rated than the IIci ones, I'd aim for those ratings so I had a universal solution.

Actually from what I’m finding the IIci required 12amps 5v and the Q650/7100 required 15amps. Do you have a reference that indicates the 7100 is higher than 15amps @ +5v?
Posted by: Phipli on 2023-03-25 05:20:32
Actually from what I’m finding the IIci required 12amps 5v and the Q650/7100 required 15amps. Do you have a reference that indicates the 7100 is higher than 15amps @ +5v?
I hadn't checked the figures, I was just saying the later ones were higher.
Posted by: MrFahrenheit on 2023-03-25 05:48:19
It looks like the LPT102-M from Artesyn Embedded Technologies might work for >14amps.


This PSU has 18a on +5v, 9a on +12v and 2.3a on -12v. I found stock at a supplier for around $95 US.
Posted by: MrFahrenheit on 2023-03-25 05:54:34
I think if I were in your position I'd give it a go, although you'd lose soft power, which would be a bit of a pain.

My only thought is that in the spec, the minimum current draw on the 12V line is given as 0.2A. What I can't tell from the datasheet is whether not meeting the minimum current draw will also affect the 5V and -12V lines' regulation. I'm guessing probably not, meanwell stuff I've had has been better built than that, but be aware it's a possibility that you might need to add a bit of extra load to the 12V and/or -12V line to stabilise things.

Here's the datasheet for the series, which isn't linked from the page you were looking at I think: https://docs.rs-online.com/58ee/0900766b81621f56.pdf

What are your thoughts on the Mean Well RT-85b for the IIsi, instead of the RPT-75b?

RT-85-MEAN WELL Switching Power Supply Manufacturer

MEAN WELL is one of the world's few standard power supply mainly professional manufacturers, covering 0.5 to 25,600W products are widely used in industrial control, medical and other fields, in line with international safety certification, short delivery of spot inventory.
www.meanwell.com
Posted by: Phipli on 2023-03-25 07:01:02
These look interesting :


There are two versions, one with a stronger 5V. They support fairly low min currents, and soft power would work.

Not sure of the logistics of a mod, but they are smaller than a IIci PSU.
Posted by: cruff on 2023-03-26 08:36:36
Don't let a minimum current draw stop you, you are only one suitably spec'd resistor away from using it. Or maybe add a LED lighting strip.
Posted by: superjer2000 on 2023-03-26 21:09:14
I replaced my IIsi PSU with a Seasonic ssp250sub. Works great. I have a little transistor circuit that maintained soft power. (did same mod with a IIci)
Posted by: pizzigri on 2023-04-15 00:41:56
Seasonic psu are only available used and the ones from Ebay need to be recapped just like the psu they’re intended to replace.
at least the ones that have been mentioned here in MLA.
I’d also love to hear from EU MLA’ers a source for a SFX format PSU that can be used for all these vintage Macs.
Posted by: Melkhior on 2023-04-15 01:12:59
Seasonic psu are only available used and the ones from Ebay need to be recapped just like the psu they’re intended to replace.
at least the ones that have been mentioned here in MLA.
I’d also love to hear from EU MLA’ers a source for a SFX format PSU that can be used for all these vintage Macs.
The one mentioned by @superjer2000 , the SSP-250SUB, is current; there's stock at Amazon Marketplace France (so seller is not Amazon). I also see stock for the outrageously priced SSP-300SUG (B are Bronze, G are Gold for the 80+ standard). They are Flex-ATX, not SFX, but that fit in the IIsi. You can see the dimension of the standards in this Silverstone page. Flex-ATX has many available options new - and they are all very expensive compared to their ATX brethren...
For 'SFX, the SilverStone SST-ST30SF mentioned by @Phipli also has stock for the current V2 (the one with weaker 5V, but still 16A), and there's some more from e.g. Be Quiet! (SFX Power 3 300W). Though, like for Flex-ATX, SFX are much more expensive that regular ATX.
Posted by: MrFahrenheit on 2023-04-15 02:52:51
I have two Corsair SFX power supplies. They’re really small and work great.

I currently use one with my G3 board and I intend to use it when I place the G3 board inside another (non-G3) Mac case (a project that I haven’t finished yet).
Posted by: f17 on 2024-02-13 10:17:45
@MrFahrenheit Did you ever end up trying this? I spent about 2 hours desoldering almost every component for a totally trashed IIsi PSU yesterday. A few lands are gone and I suspect I will never make this one work again. I've got one more I'm almost afraid to even open. So I'm looking for any alternative here. Even losing soft power would be a small problem compared to not being able to use the computer at all.
Posted by: MrFahrenheit on 2024-02-13 13:55:48
@MrFahrenheit Did you ever end up trying this? I spent about 2 hours desoldering almost every component for a totally trashed IIsi PSU yesterday. A few lands are gone and I suspect I will never make this one work again. I've got one more I'm almost afraid to even open. So I'm looking for any alternative here. Even losing soft power would be a small problem compared to not being able to use the computer at all.
@f17 No I haven't touched any of that stuff since writing that back in March 2023.

I don't know what to tell you. I had started some research on this, and then I just gave up for now. I wish I had better news.
Posted by: chiptripper on 2024-03-10 12:49:28
@MrFahrenheit Did you ever end up trying this? I spent about 2 hours desoldering almost every component for a totally trashed IIsi PSU yesterday. A few lands are gone and I suspect I will never make this one work again. I've got one more I'm almost afraid to even open. So I'm looking for any alternative here. Even losing soft power would be a small problem compared to not being able to use the computer at all.
I have the guts from a IIsi PSU. It’s pretty clean. Only real damage is to the sub-board with the two very leaky SMD caps (which I assume controls soft power). That’s toast, so I am planning to attempt a Meanwell transplant.

If you want the guts to fix your trashed PSU, you’re welcome to it for the price of shipping. I’m just across the water from you in Victoria.
Posted by: f17 on 2024-03-10 12:59:27
I have the guts from a IIsi PSU. It’s pretty clean. Only real damage is to the sub-board with the two very leaky SMD caps (which I assume controls soft power). That’s toast, so I am planning to attempt a Meanwell transplant.

If you want the guts to fix your trashed PSU, you’re welcome to it for the price of shipping. I’m just across the water from you in Victoria.
Thank you. I will keep this in mind. Just in the short time since I posted this, I found that I have more IIsis that I knew about and at least one of them is missing the top case, so unless more than one has an absolutely destroyed PSU, I should have enough PSUs for each machine with a complete case. That said, the most recent one I opened has a lot of green goo in the connector of the power supply, so we'll see. I think the little daughter board actually survived in the one I was talking about. It might be the only part of it that did. Also I discovered that there is another version of the power supply for these that is riveted shut and is essentially on repairable. However, I think I have two of those and there is no sign of any leaking inside or in the connector, and I used a flashlight to get a pretty good look inside, so I'm fairly confident that those are going to be okay. I'll try to document what happens with these.
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