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Richard Crowley Richard Crowley is offline
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Default Amplifier Problem - Revised Schematic

"EADGBE" wrote ...
I have just discovered that the voltage measured directly at the
emitter leg of Q208 is a NEGATIVE voltage that fluctuates anywhere
from -300mV to -16mV.


You show the collector of Q208 as being ground.
Is that same ground not the reference for all your
reported voltage measurements. How could it
possibly be negative? There are no sources of
anything below ground shown in your schematic.

What is the voltage on the "to volume control pcb"
node at the bottom left corner of the circuit? Is it
ground/zero? Is that node *really* disconnected
from the rest of the ground reference (collector of
Q208, bottom of the 680 resistor, etc.)? It seems
like it ought to be ground, but you show it as a
separate node.

It seems suspicious that the base of Q204 is measured
to be the proper voltage, but the collector seems to
be pretty much up at the supply rail. That indicated to
me that Q204 isn't conducting properly and preventing
proper bias on Q205.

We have asked you several times about measuring the
equivalent nodes in the other (working) side, but you
seem to have ignored this valuable source of information
about how a proper circuit behaves.