Astec AA21660 power supply modification for 13.8V output

Astec AA21660 power supplies can be modified to give 13.8V / 24A.

They are specified to 24A @12V and 27A @5V, with 400W max continuous power. It is used in various  Engenio (former LSI Logic) storage products, which are OEM-ed by many companies: IBM (TotalStorage DS4xxx and DS5xxx line), NetApp etc. The IBM FRU is 19K128.

The following mods change the overvoltage protection to 14.4V, and set the voltage to 13.8V.

Locate IC13, IC11 and R70:

Astec AA21600 SQ5BPF mod 1

Solder 100k between IC13 pins 10 and 12, and 1k between R70 (left pin, near the AC input side) and IC11 pin 12. This sets the overvoltage protection to 14.4V.

Astec AA21600 SQ5BPF mod 2

Cut the narrow trace left of  the +12V trace. Between the +12V trace and the narrow trace insert a 370ohm resistor (I used 470 + 2k2 + 4k7 parallel), or a 470ohm potentiometer.

Short the pad on the left to ground (the pad on the left side of the +5V pad).

Astec AA21600 SQ5BPF mod 3

Turn on and check the output voltage under a load of at least 1A (a car light bulb can be used as a load resistor). If a potentiometer is used, then adjust it to get 13.8V.

This power supply needs forced air flow if continuous high current is drawn from it.  If so, install a fan.

VY 73 de Jacek / SQ5BPF

Warning: this device contains lethal voltage inside. Don’t play around with this equipment  unless you know what you’re doing.