MOTM

Recently I shuffled some units around, pulled the 960 out of the system and 
put it back. I've noticed that now the + voltage takes an eternity to settle 
after powering up. It will swing up to 15.6v and then drift randomly between 
that and 14.8v for maybe 15 minutes before finally settling on 14.9, while 
the - voltage heads right to -14.9 and stays there, rock-solid. I've had a 
meter hooked up for the last few days trying to figure out the pattern.

I'm inclined to say that the problem isn't due to the PSU, which is a dotcom 
NOS by Power One, because my dotcom VCO doesn't drift in pitch at all but 
the two MOTM vcos do, together, and along with the + voltage. The 960 is the 
only thing between the PSU and the MOTM units, so it's the only thing that 
appears wonky.

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This is very odd. It sounds like the Power One is unstable, the LM723N on 
the Power One is 'wandering'. They have a built-in Zener diode reference, 
maybe it is drifting around with temperature. You can try disconnecting the 
'960 from the Power One, and see if it still wanders around.

If it still does, you might get lucky and if it's in a socket you can get 
new ones from Mouser/Digikey for <$1.

If if does *not*, then:
a) are you exceeding 80% of the rated current? You might have an in-rush 
power issue. The +15V current draw is probably 2X the -15V draw. Use the 
meter to check the *current* on each supply line.

b) a new LM723N might still be the fix. If both of the parts are in sockets, 
swap them and see if that fixes it (there may even be 3 on there if there is 
also +5V).

c) you can see if it really is the '960 by keeping it connected to the Power 
One, but unplugging all the modules to it.

Paul S.