Repairing "open frame linear" modules

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Brian Roth

Well-known member
Joined
Aug 20, 2005
Messages
3,185
Location
Salina Kansas
I'm beginning to collect more than a few "blown" Power-One, Condor, International Power units here. I have exactly ONE schematic (for a 15VDC @ 15Amp module) that came via Amek...they used many of those modules in the 9098i desk. Sidebar: Amek had a "factory sanctioned" mod to raise the output voltage to 18V, and slow down the overcurrent protector so the inrush current wouldn't shut-down the module at power-up.

Today, I replaced a bipolar 15VDC/5A module in the power supply rack frame for an Otari Concept One recording desk. I could smell something vaguely burnt, but nothing was obviously charred on the regulator card. Time Is Money, so "in went" a new International Power module to replace the OEM Power-One module, which was date coded 1993 and has been running 24/7 ever since.

Curious if anyone has "factory" schematics for these various modules on-hand since it's NOT worth my time to trace the foil on the regulator cards.

Bri, collector of open-frame "door stops" <g>
 
I have fixed a number(few hundred) 723 based power supplies over the years. The lamdas seem to last the longest. What I found was the cap used on the voltage X2 part dries up, pops off the board etc. The X2 is so the circuits can use a NPN(s) series pass.

The NPN needs more voltage than the regulated output voltage at the base so the drive circuit is at a higher voltage than the main raw supply.

What happens is you first get a lot of ripple on the output under load. A lot of times the big caps are fine it is often just the X 2 cap.

most supplies seem to be based off the 723 app note. The app note was in an old RCA soft cover book IIRC.

look for a diode and cap off the main diode bridge.

Books often show NPN low side and PNP high side switches. The PNP with a + supply just needs it base "pulled" closer to ground to turn on more. I guess PNPs cost too much or were not a good as cheaper NPN power transistors.
 
I vaguely recall seeing the "extra" xfmr winding and associated circutry on the International Power 15V/15A module used by Amek, but I don't know if that was a universal design in all of the jillions of variants.

The failure modes I've encountered are all over the map.

Bri
 

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