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#1 2015-07-02 09:46:23

mc680x0
Member
From: Sydney, NSW, Australia
Registered: 2014-06-14
Posts: 8
Website

Macintosh IIsi/ci/cx PSU requirements

So, as my IIci PSU has bitten the dust, as has the hot-spare; it's time to investigate Alternatives.

I've found a pinout for the PSU that suggests the rails are +12, -12, +5, -5, as well as a +5V pin that directly feeds the power-on circuit, and a "power good" signal.

Is the "power good" comparable to the PWR_OK defined in the ATX 1.0 spec? If not, what does it actually do, and what does it expect when the power is, in fact, good?

Also, is the power-on circuit power a persistent voltage that's fed to the board at all times (i.e. when the PSU is plugged in but the system is not turned on)?

I recall something about the ASTEC PSUs having an internal failure pertaining to the power-on circuit, that can be fixed with replacement diodes or some such; while repairing the PSU is a good option for a machine that is intended to run in "authentic" condition, I actually have another project that would benefit greatly from the PSU no longer occupying quite so much space.

Thanks for any light you guys can shed!


Doing perverse things to Apple Computers since 1996.
I wonder what this wire goes t- /kzzzzt

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#2 2015-07-02 13:13:05

TheWhiteFalcon
Member
Registered: 2015-04-27
Posts: 504

Re: Macintosh IIsi/ci/cx PSU requirements

I'd post some links on this very issue but the site they're on is offline at the moment. Yes, the common issue is the 5v trickle power circuit.

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#3 2015-07-02 15:33:08

jt
Member
From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,470

Re: Macintosh IIsi/ci/cx PSU requirements

Maybe they're busy restoring content obliterated in The Great Pixel Robbery!

.  .  .  or not. roll


I was working on the design a conversion PCB to put a relatively powerful, tiny, ATX PSU into the IIsi PSU's sheet metal. See above. hmm

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#4 2015-07-09 09:44:52

mc680x0
Member
From: Sydney, NSW, Australia
Registered: 2014-06-14
Posts: 8
Website

Re: Macintosh IIsi/ci/cx PSU requirements

jt: I'm trying to figure out something roughly similar so I'll have the space to put heatsinks on my PowerCache and maybe upclock it a little bit. I hear the later 800nm 68030s can clock up to about 58MHz so long as there's something to draw the heat away, so 55MHz shouldn't be too much to ask for parts binned at 50MHz smile

Such an interposer board is certainly possible, but to do it right requires an understanding of the PWR_GOOD/PWR_OK and 5V_TRKL rails and if they behave in the same manner or inverted relative to the ATX 1.0 spec. It would also be helpful to know what the draw tends to be on those rails, but that's the sort of thing that of course varies from system to system. (For instance, the few IIcis with a parity chip would draw more 5V than non, hard drives vary, accelerators, et c.)


Doing perverse things to Apple Computers since 1996.
I wonder what this wire goes t- /kzzzzt

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#5 2015-07-09 18:28:33

bobo68
Member
From: Germany
Registered: 2015-07-07
Posts: 22

Re: Macintosh IIsi/ci/cx PSU requirements

Try to find a copy of Apple's Giude to the Macintosh Family Hardware - a great resource. The pinout of the IIcx/ci PSU is a follows:

If you look at the PSU's plug with the little indicator (which prevents wrong insertion of the plug) pointing upwards, pin 1 is at the lower left, then it goes to pin 5 at the lower right, the pin 6 upper left, pin 10 upper right.

Pin
1: +12 V
2-4: +5 V
5-7: Ground
8: -12 V
9: /PFW, power fail warning
10: +5V.TRKL, supply for the startup curcuit

To my knowledge /PFW serves a double purpose:
power fail warning - ahem, of course. It goes low a few fractions of a second before the PSU fails to supply power
start up: if fed with +5V, the PSU starts up

So you can shorten pin 9 and 10 and the PSU willl start.

HTH, bobo68

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