Old power supply connections question.

[Loose rivets]

All my bench PSUs are still in storage in the UK, so to help the mini Rivets I thought I would make a temporary bench supply out of an old Morex unit. But I can't remember the requirments of the "OK circuitry." -- The line or lines that have to be linked or powered up to make the thing turn on.

The P8 P9 plugs look standard for the time RRRYBB-BB,Blu,YRO

I would be grateful if someone could tell me how to bypass the safety circuit. R

[Mac the Knife]

As I recall, the old AT power supplies just turn on - Pin 1 (usually orange) is the "Power good" signal (+5v) for the mobo to tell it that all voltages are nominal and it can safely start. There's usually a delay of 0.1-0.5sec before it goes high.

ATX PS's have a line (Pin 14) on the mobo power connector called POWER ON, usually colored green (see Table 2). If you short this to the next wire (Pins 13 or 15, GND, colored black), the PS should start. The mobo usually controls this.

Just remember that switching power supplies need to see a load - either they won't start/shut down or burn up if you try to run 'em no-load! From my book*, usually a minimum load of 0-0.3amps at 3.3v, 2-4amps at 5v, 0.5-1.0amp at 12v is acceptable.

*Scott Mueller's "Upgrading and Repairing PCs" - http://www.quepublishing.com/promotions/promotion.asp?promo=1626&rl=1

[Keef]

Yes - ATX power supplies get very upset if run with no load (don't ask how I found out :( )

Is this bench PSU for a computer, or something else?

I wanted a 12v PSU to run some kit up in the Norfolk cottage. A nice 12v 15amp one with a transformer, bridge rectifier, and transistors to hold the output voltage stable was £100.

I got a switch-mode one, 13.8 volts max 20 amps for £20. It will need some added protection circuitry before I use it to power anything expensive, but at that price I don't mind.

[Loose rivets]

Thanks Mac and Keef. It's all coming back now, the loads needed to keep the PSU happy would be rather a burden to contrive, just to give me a bench PSU with two fixed voltages.

I used to use some CB radio power units for odd tasks. The voltage control was somewhat basic and I could put a pot in and control the v with that. They were well built and cost nowt as CBing lost its popularity. I never did purchase one of those all singing units with LEDs showing the current and voltage. They were always just that little bit too expensive.

I was lucky to have a good scope, which I got in exchange for rebuilding a Sony camera. 0 to 100 Mhz Iwatsu Sp? But I sold that when I was packing up my home.

All of this is old-hat now I suppose, as a humble PC can be made to do most measurements...and indeed record the data forever. One will have to see if the grand-sprog is really interested before making him the excuse to buy more toys.