At 10:28 AM 07/13/12, Eric Lemmon WB6FLY wrote:

You asked what the MU1 IC in the Astron SS-30M power supply was.  It 
is the "workhorse" PWM chip TL494CN.  The IC is mounted on a module 
that is about 1.25 inch by 1.75 inches and has nine header pins on one end
that are soldered into the main PCB.  All of the reference numbers that
begin with "M" are mounted on this module.  I examined the parts on the
module and identified them as follows:

MC1 - 50 uF 10V electrolytic
MC2 - 0.1 uF Mylar
MC3 - 0.022 uF Mylar
MC4 - 0.001 uF Mylar

MR1 - 10 k
MR2 - 8.2 k
MR3 - 2 k
MR4 - 15 k
MR5 - 150 k
MR6 - Zero Ohm Jumper
MR7 - Not Used

MD1 - Not Used
MD2 - Not Used

The switching frequency is fixed, and is set by MC4 and MR4, which are
connected to IC pins 5 and 6 of the TL494CN.  With those values, the
switching frequency works out to be about 73 kHz.

I could not identify most of the resistors on the main PCB, because the
designators were under the components and could not be seen.  I did notice
that diodes D23 and D24 were not used; the 12 VDC cooling fan is controlled
by a thermal snap switch on one of the heat sinks.  A similar thermal switch, 
on the other heat sink, will open the AC input line when triggered.
Neither thermal switch appears on the schematic which came with the unit.
As is typical with Astron schematics, it is "representative" of the
circuitry, but it is by no means accurate.

73, Eric Lemmon WB6FLY