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IBM PS/2 Model's 70 PSU: what is the System Status pin?

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First post, by seleryba

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Hi Folks. I have an IBM PS/2 Model 70 with broken power supply.

I decided to swap internals of the supply with some modern ATX SFF one. I did it before with one of my IBM PC330 - a lot of cables to manage, but at all the pinout was like a standard AT/ATX power brick.

In this case it's not that easy. I found the pinout on the web:

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and while most of that are easy-peasy (-12V/+12V/+5V/POWER_GOOD, DC RETURN is just a GND), one label is unclear.

SYSTEM STATUS.

Do you know what's that and how to provide an equivalent from a ATX supply? Is that something hard-connected to the +5V/+12V/GND rail or something more complicated?

Reply 1 of 4, by pentiumspeed

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One of the pin is for hard drive LED output to PSU, keep in mind if you want to use LED for hard drive or use a MCA SCSI card which is way easier to obtain than the limited choice of MCA hard drives.
That's for hard drive LED aka system status. IBM speak. 😀

Cheers,

Great Northern aka Canada.

Reply 2 of 4, by seleryba

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pentiumspeed wrote on 2021-02-27, 03:54:

That's for hard drive LED aka system status.

Thank you @pentiumspeed! So I can leave it unplugged for the testing purposes and it should boot?
BTW, how it works? PSU outputs the HDD led data? How does it know the HDD activity status?

Reply 3 of 4, by pentiumspeed

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don't know. You could trace the circuit inside the PSU?

Leave "system status" unconnected is no issues.

Cheers,

Great Northern aka Canada.

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