Re: Amplifier Problem - ***SOLVED***

On Tue, 22 Apr 2008 12:38:19 -0700, "Richard Crowley"
<rcrowley@[EMAIL PROTECTED]
> wrote:

>"EADGBE"  wrote ...
>> That's when I found it -- a *microscopic* crack in the trace between
>> the emitter of Q208 and its adjoining 3.3 ohm resistor.  The crack was
>> so incredibly tiny that I easily overlooked it--repeatedly.
>>
>> I took one of my jumper leads and clipped one end of it to Q208's
>> emitter and the other end of it to the 3.3 ohm resistor.
>>
>> I then took voltage measurements.  EVERYTHING WAS NOW ON SPEC:
>
>Its hard to imagine how the output node (where the two
>3.3 ohm resistors join) could be correct (6.4V) without
>the path through the lower 3.3 ohm resistor and Q208?
>

Pure coincidence - it was the breakdown voltage of the reverse biased
base-emitter of Q207.

>But at least you got it working. Good for you. Trouble-
>shooting  ("fault-finding" as they call it in the UK) discrete
>circuits is rapidly becoming a lost art. 
>
Quite so - when all the components are right, but there is still a
problem, go for the board.

d

-- 
Pearce Consulting
http://www.pearce.uk.com