Jump Start Macintosh IIsi PSU

[plb007]

Hi everyone, I just recapped the MB and PSU from a IIsi. With the PSU out of the computer, I have a nice 4,96V from the 5V stand by line. How can I start the PSU without putting it in the computer. Which pin of the 10 pin connectors tells the PSU to start ? I want to do this before putting the PSU in the computer so I can check the output voltages.
Thanks

 

[Phipli]

Hi everyone, I just recapped the MB and PSU from a IIsi. With the PSU out of the computer, I have a nice 4,96V from the 5V stand by line. How can I start the PSU without putting it in the computer. Which pin of the 10 pin connectors tells the PSU to start ? I want to do this before putting the PSU in the computer so I can check the output voltages.
Thanks

I believe you want to apply the 5v to the /PFW pin. It needs to be kept connected (the logic board would latch it)

Note that PSUs often don't show the correct voltages when not loaded, and sometimes won't even start without a load.

The best, and only reliable way, to do what you're trying to do, without connecting the board, would be to use a dummy load.

 

[plb007]

Thanks, when plugged, my PSU shows only 5V on pin 10, which seems correct as this pin is the 5V stby line. What does the motherboard do with this 5V to tell the PSU to start ? (applying this voltage elsewhere, shorting, .... ) I can put a dummy load on the 5 and 12 volts lines if necessary, but I first need to start this PSU.

 

[Phipli]

Thanks, when plugged, my PSU shows only 5V on pin 10, which seems correct as this pin is the 5V stby line. What does the motherboard do with this 5V to tell the PSU to start ? (applying this voltage elsewhere, shorting, .... ) I can put a dummy load on the 5 and 12 volts lines if necessary, but I first need to start this PSU.

I said above?

I believe you want to apply the 5v to the /PFW pin. It needs to be kept connected (the logic board would latch it)

 

[Phipli]

 

[robin-fo]

I believe you need to connect the 5Vstby to /PFW *and* have enough load on the normal 5V and maybe also the other lines as well

 

[Phipli]

I believe you need to connect the 5Vstby to /PFW *and* have enough load on the normal 5V and maybe also the other lines as well

Yes, that's what I said.

Today is one of those days. I'm going to give up soon!

 

[plb007]

Ok, I understand now how it works in detail compared to ATX PSU. It's "just" a simple link from pin 10 to 9 (with resistor ?), to power this PSU.
Unfortunatly, when checking, I link pin 10 & 9 with a 1 k resistor and something blew inside the PSU (not instantly, but after some times). Those PSU are really complicated to rebuild. I'll switch for an ATX PSU ...

 

[Phipli]

(with resistor ?)

Nope, just short it.

 

[Phipli]

Unfortunatly, when checking, I link pin 10 & 9 with a 1 k resistor and something blew inside the PSU (not instantly, but after some times). Those PSU are really complicated to rebuild. I'll switch for an ATX PSU ...

Shame, guessing it is an Astec. They don't seem to be surviving long term.

There might be some useful stuff in these threads :

Stealth Macintosh IIcx/IIvx style SFX PSU rebuild

Hello, I've been asked to post this here on IRC so there it is. A lot of PSUs from this era are bad quality and difficult to repair (if possible at all). One of the worsts is the Astec AA15830 (Apple P/ 699-0392) One of the solution is to use the excellent adapter board by @blusnowkitty and...

68kmla.org

IIci etc. ATX to 10pin Adapter

A friend designed an adapter for converting ATX to connect to a IIcx, IIci, IIsi, Q700, C/Q650, IIvx, IIvi, P600, Q800 and 7100. Handy for bench testing, and with a little work on mounting, may help with replacing PSUs. He has shared the design. You're free to make some for yourself. I've...

68kmla.org

The first shows how to replace the guts of a IIci PSU (which is the same, but physically bigger). This solution discusses hard wiring the soft power, the computer comes on as soon as you switch on the PSU, as well as soft power discussions.

The second is a little adapter board that adapts from ATX to IIci/IIsi, and sorts out soft power. You can order your own if you're comfortable doing so. You can get the manufacturer to do the surface mount soldering and source your own molex connectors (or just wire in the existing cables if you feel like it). Need to fix it somewhere so it doesn't short to any metalwork. DIY project

 

[plb007]

Thanks for all the links. I already did some ATX conversion without the soft power mod. My first attempt with this mod (soft power) was a fail. I use seasonic PSU as they have enough power ans small form factor to fit in a IIcx PSU.
The IIsi PSU looked fine (and it's a SONY PSU) so I decided to try a recap (I didn't try anymore with IIcx style PSU) without luck.
Regarding the soft power, I have a relay that I want to try This one .