MOTM

Or modify the power supply.

The Power One dual linear supplies suffer from what is called common 
mode latch up. As Paul says this is to do with the largish amount of 
capacitance that the supply has to charge up.

Power One were initially very secretive about this when I contacted them 
about that, but a little while later my e-mail managed to get to someone 
who was a little more sympathetic to our needs.

He suggested [in caps]:

1) JUST TURN UP THE CURRENT LIMIT SLIGHTLY.  THIS SHOULD WORK IF YOU ARE 
EXPERIENCING BOARDER LINE TURN ON CURRENT.

This is the trimmer that usually has a little gunk on it to stop it 
being moved.

2) ADD CAP AND RESISTOR IN SERIES FROM U1 PIN TWO TO U1 PIN THREE.  CAP 
VALUE TO BE BETWEEN 10\ufffdF TO 47\ufffdF WITH A 16VDC RATING OR HIGHER. 
RESISTOR VALUE TO BE BETWEEN 150ohms TO 220ohms.

I didn't find that this worked that well.

But what I did eventually was much more drastic. I removed many of the 
components around the LM723s and rebuilt the it as the datasheet shows 
[you can look in Horowitz and Hill and also the Elektor Formant too]. I 
used a standard current foldback method, with current limit set to 0.8A 
as before but with a foldback limit of 0.4A.

This worked very well. But it should be noted that this its about a half 
an hours work and you need to know what you are doing. The trimmer will 
need to be removed, as will a few resistors including the main current 
limiter.

I'm saying no more now. If you can do the calculations needed to get the 
values right you should be able to do the job. If you can't then you 
shouldn't be playing with a power supply.

Needless to say that if you mess it up you could fry your whole modular 
or worse, yourself.

If in any doubt at all, buy another supply.

Tony