Need some help with an Atari Switching Power Supply

Hello Again - Happy July 4th!

I'm trying to fix an Atari Switching Power Supply out of an I,Robot game
and I'm a little stuck. This is the first time I've worked on one of these.
 I'd like to see if I can fix this instead of replacing it with a new
switching power supply because this one also includes the audio amp.

Here is some info:

1) If there is no load at all on the power supply, I can read +5v on my
DMM. As soon as there is any load, the regulator shuts down and the LED
lights up.
2) The +12v supply is good
3) The following components have been replaced; The 3525a regulator at U1,
the LM339 comparator, and the two Mosfet Transistors

Here is the Schematic for reference. ->
http://games.rossiters.com/manuals/ir_ps1.jpg

Questions:

1) I'm not seeing pulses on pins 11 and 14 of U1 - which are supposed to
power the T2 Transformer. http://games.rossiters.com/manuals/pulses.jpg
(Diagram 1)
On U1 - Pins 5 and 7 I'm seeing a sawtooth wave form, but on pin 6 I'm only
getting a flat 5volts. The manual says "Resistor R7 and Capacitor C10 set
the frequency of the U1 oscillator while R8 and C10 set the dead time."
Should I be seeing some sort of wave form on pin 6?

2) I'm assuming I'm supposed to measure the test points with an
oscilloscope the same way I usually do right? (i.e. Ground lead goes to
ground, other lead goes to test point). I'm not getting any reading from
those test point.

Thanks!

Matt

Other reference material -
Atari Switching Power Supply Manual ->
http://games.rossiters.com/manuals/Atari_Switching_Power_Supply.pdf
3525a Pulse Width Regulator Datasheet ->
http://games.rossiters.com/manuals/4286.pdf

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Thu Jul 3 21:33:59 2008