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Modern PSU for the SE/30


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Lots of possible explanations there - it could be measuring average load over X amount of time.

 

Would be easy to test if anyone cares - plug a Seasonic PSU out of the box with no load into the wall, then point a hairdryer at it.

Edited by Crutch
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Well, I'm not going to take out the SEASONIC from my SONY PSU chassis only to blast it under no load with a hairdryer.  But back in 2018 I made the video below which serves to better explain what I said in my previous post, showing very clearly that "high current" does not appear to trigger the fan.

 

 

Edited by JDW
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Good and clear video as usual.  Did anyone respond confirming similar behavior?  The statement on the spec sheet that the fan doesn’t run under a 30% load is so specific it’s hard for me to believe they just completely made it up and the fan really is just temperature controlled.  I have a spare Seasonic PSU, maybe I will try it this weekend.

 

Edited by Crutch
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5 hours ago, Crutch said:

Did anyone respond confirming similar behavior?  I have a spare Seasonic PSU, maybe I will try it this weekend.

No one responded, so I look forward to your test results this weekend! :-)  No doubt you'll confirm what I show in my video.  I doubt the unit I have is unique.

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I just installed a SSP-250SUB in one of my SE/30s and I am not getting good results at all.

The 5V line is at around 4.8V with just the logicboard and some RAM and no PDS cards. It drops to 4.6V if I add a network card and down to 4.2V (resulting in a non-booting Mac) if I add an accelerator on top of that.

Exchanged the power supply for another unit just to make sure it is not faulty - same results.

I am running a spinning hard drive so there is at least some added load on the 12V rail.

 

I can not recommend doing this unless some other modification is done to get a stable 5V output... I am going to experiment with additional dummy loads on the 12V and 3.3V rails. This kind of defeats the purpose of a modern power supply though because adding a dummy load to the 12V line is a thing I already have to do on some of my stock Sony power supplies to get the 12V rail back into spec.

Edited by Bolle
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4 hours ago, Bolle said:

I just installed a SSP-250SUB in one of my SE/30s and I am not getting good results at all.

The 5V line is at around 4.8V with just the logicboard and some RAM and no PDS cards. It drops to 4.6V if I add a network card and down to 4.2V (resulting in a non-booting Mac) if I add an accelerator on top of that.

 

I had the same problem until I checked the main wire harness that connects the Analog board to the motherboard.  A couple wires were higher resistance than they should have been.  Since I didn't have the required terminals to merely swap out the wires, I soldered on a wire in parallel with each of the bad wires and the voltage then tested right at about 5 volts at the external floppy connector.  So it could be a high resistance wire (due to age) or corrosion on the terminals inside the connector or both.

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4 hours ago, JDW said:

 

I had the same problem until I checked the main wire harness that connects the Analog board to the motherboard.  A couple wires were higher resistance than they should have been.  Since I didn't have the required terminals to merely swap out the wires, I soldered on a wire in parallel with each of the bad wires and the voltage then tested right at about 5 volts at the external floppy connector.  So it could be a high resistance wire (due to age) or corrosion on the terminals inside the connector or both.


This is a problem I've encountered in some late 70s/early 80s micros so there's potential for it to be at least partly to blame here. A complete harness transplant fixed all the issues on my old Heathkit, which seemingly couldn't hold voltage even after a total PSU rebuild. I'm very curious to see how things develop on the Mac side of this issue.
 

As for how or why old wiring becomes more resistive I have no idea. Oxidisation? 

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6 hours ago, PowerMac_G4 said:

A complete harness transplant fixed all the issues on my old Heathkit, which seemingly couldn't hold voltage even after a total PSU rebuild. I'm very curious to see how things develop on the Mac side of this issue.


I wonder if this is just good due diligence with machines this age; i.e. if replacing the wiring harnesses all around should be required. I mean, it's all Mini-Fit Jr. (thanks, @cheesestraws) receptacles, right? Even though I really dislike crimping, perhaps this will avoid the problems?

Here are PNs I've found (checked against an AB image and molex'sCAD viewer):
2x5 receptacle: https://www.molex.com/molex/products/part-detail/crimp_housings/0039012100
2x6 receptacle: https://www.molex.com/molex/products/part-detail/crimp_housings/0039012120

2x7 receptacle: https://www.molex.com/molex/products/part-detail/crimp_housings/0039012140


I think JDW references the CRT receptacle and board plug in his analog board re-cap video, because I don't know it off hand :lol: if that's another one to do out of due diligence.

What wire gauge should one use, if they were to tackle this challenge?

 

Which invites another question I had: the OE harnesses that come with the SeaSonic PSUs have 4-pin molex power coming out of them. Is there any harm in splicing off of them (fan power mainly) instead of using the analog board's connector? My gut says "no problem" because some folks aren't installing a spinner to draw from anyway, however my gut is also not an electrical engineer ;) 

This is all very timely, as I was considering a swap, as well as implementing Bolle's adapter+NIC with an accelerator.

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4 hours ago, jessenator said:

it's all Mini-Fit Jr. (thanks, @cheesestraws) receptacles, right?

 

Both the AB <-> LB and PSU <-> AB connections are mini-fit jr. on both ends.  I don't have an SE AB out right now to check what connectors the other AB cables are. 

 

For people who are good at crimping and cable-building, replacing those cables might not be a bad plan.  For people like me who are terrible at it, it is less likely to help ;-).

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4 hours ago, jessenator said:

What wire gauge should one use, if they were to tackle this challenge?

 

Answer: The thickest wire that can be used to fit the terminals in a compatible connector.  As such, I do not believe you can go thicker than the stock 18AWG wire.  If you could, that would be great.  The thicker the better, especially for an upgraded SE/30.

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4 hours ago, jessenator said:

I wonder if this is just good due diligence with machines this age

The folks over at the Society of Eight Bit Heathkit Computers certainly seemed to think so. It's fairly normal for cars to need new wiring once they approach 30-40 years old so it figures that computers of that age do too. The fact that those kit computers sometimes required the builder to make their own wiring harness compounds the issue. I've read a few accounts of machines with wiring that was two thirds or even half the gauge it should have been – scary stuff when you're working with old-school CRT boards. 

 

4 hours ago, jessenator said:

What wire gauge should one use, if they were to tackle this challenge?

I would strip some of the old wiring and measure the gauge with a micrometer. Obviously you'll want to match both the gauge and the type of wiring with your replacements. Thicker wiring would be advantageous for upgraded systems.

 

I sure am jealous of the upgradeability of other compact Macs. I have a lowly Classic so the upgrade path is somewhat more complex than any other compact.

Edited by PowerMac_G4
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4 hours ago, JDW said:

As such, I do not believe you can go thicker than the stock 18AWG wire.

 

Yup.  Per Molex's website, the biggest is 18AWG (c. 0.8 mm² for those of us in metric lands) in the normal mini-fit terminals.  You can get terminals to push into the mini-fit jr shells that go down to 16AWG, but I think those require matching high current terminals at the other ends.  (I may be wrong; I am not an expert, just someone who worries too much about connectors).

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9 hours ago, JDW said:

until I checked the main wire harness

You sir are the hero of the day.

I was running this on my testbench setup with an extension cable and believe it or not one of the two 5V pins slipped out of its seat in the connector housing and wasn’t making good contact.

After crimping on a new contact everything is now running well. Voltage on the 5V line still is a little bit on the low side with 4.7V, but at least it’s staying there no matter if there’s no card installed at all or if I am running 2 PDS cards + accelerator.

It also seems that while the stock PSU would not be able to run the Turbo040 stably at anything below 4.8V the replacement PSU handles this just fine.

Might still see if I can adjust the voltage a little bit closer to 5V.

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Great tip @JDW.  I have a recapped SE/30 analog board with a Seasonic PSU that isn’t getting the floppy port voltage anywhere near 5V ... definitely going to give replacing the harness a try.  I would not have thought of that, obvious as it is.

 

(Still haven’t tested out if I can trigger my Seasonic PSU fan with heat .... one day soon!)

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Thanks for the great insight @JDW! I wonder if anyone is interested in making replacement SE/30 wiring harnesses? Making these is a huge pain for me, and I imagine there'd be healthy interest here if they're a weak link in SE/30 maintenance.

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19 hours ago, nickpunt said:

Thanks for the great insight @JDW! I wonder if anyone is interested in making replacement SE/30 wiring harnesses? Making these is a huge pain for me, and I imagine there'd be healthy interest here if they're a weak link in SE/30 maintenance.

 

Replacement, thick-wire harnesses for the SE & SE/30 might prove a popular item if the selling price is right.  I've just been too busy with work and videos to rebuild any myself.  With all of the products and accessories on the market for vintage Macs these days, I'm a bit surprised no one has addressed that need yet.  I guess it's just assumed everyone will build one themselves.  

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On 3/31/2021 at 5:11 AM, JDW said:

Replacement, thick-wire harnesses for the SE & SE/30 might prove a popular item if the selling price is right.

 

This is the kind of thing that can be done well by automated machinery, definitely this comes down to someone making the dive to start doing so.  Now that the prospects of replica logic boards are floating around, I'm guessing this is getting closer to someone's radar to try out.

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On 4/3/2021 at 5:53 PM, quorten said:

Now that the prospects of replica logic boards are floating around, I'm guessing this is getting closer to someone's radar to try out.

Maybe not.  Think about how complex a motherboard is, and yet someone came out with one because they wanted it that badly.  A wire harness is far, far less complex, yet no one has released that yet, despite the need.  It really comes down to will.  For where there's a will, there's always a way.  

 

Perhaps if more machines were failing left and right due to that harness, the will to create new harnesses would exist.  But for now, we simply have low voltage problems and intermittent operation.  Most people don't point to the harness when that happens, and as such, we don't have a market for replacement harnesses yet.

 

But by all means, if someone comes along and creates a batch of new wire harnesses, I think that would be wonderful.  Maybe my pessimistic post will inspire someone to do just that.

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