MOTM

On Wed, 3 Jun 2009, funkyfortyatyahu wrote:

> #3 looks good when controlling by Eye, i can't see any wrong wiring, shortcuts or anything else.
> Any more advice ? Paul ?

There is only one way for the circuit to work but there are
infinite ways it can fail.  It may be impractical for anyone
to identify your particular problem.

But as you have three working 300's and one non-working, there
is one obvious approach to take:  compare the two.  Best with
an oscilloscope.  Or paired AC/DC readings from a voltmeter (as
appropriate) if that is all you have.  Start at the summing
amplifier.  Adjust coarse knobs to give similar voltage levels
at the input.  Then work towards the MAT-02.  Identify the
anomalous input/output sets.  You have one already:  U4B
feeding MAT-02.  But something 'in front' of these may be
at fault.  U4B appears to be working backwards in your case.

--
Monty Brandenberg