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Now, if you see signals that are wildly different from this, or not with the right phase offset, or not approximately equal
amplitude - then worry about IC5 and its surrounding circuits. This is the area of the circuit to examine carefully for faults,
dry joints, incorrect component values, solder bridges, etc.
IC6 and IC7 phase shift circuits
Now it is time to check the 90-degree phase shift circuits, the four op-amps made by IC7 (I-channel) and IC6 (Q-channel).
My simple technique is to look at pin 1 and pin 7 of each of the chips IC6 and IC7. At each of these outputs I am expecting
to see a clean 700Hz sinewave and the amplitude should be practically the same as in the former 'scope screenshot. The
audio phase shift circuits are supposed to have a gain of 1.
NOTE: that the only exception to this, is the case where 1K and 3.3K are swapped. This was the case in some early batch
kits, due to an error on the silkscreen. The silkscreen wasn't changed in later batches, but the assembly manual was
altered to match the PCB silkscreen. If you built your kit using a manual version 1.00 to 1.07, then you have the swapped
1K and 3.3K resistors, R19 and R25. If you built your kit using manual version 1.08 or above (published 23-Oct-2017)
then R19 and R25 are not swapped. These two resistors R19 and R25 are next to each other on the board. R25 is closest
to the IC7 chip body near pin 8 and it is supposed to be 3.3K. R19 is supposed to be 1K and is next to the R27 I-Q
balance trimmer potentiometer. If these two are swapped, it is nothing to worry about. It means that the gain of IC7a will
be increased, so it no longer has unity gain. By good fortune (or otherwise, since it masked the problem for some time), if
R25 is 1K and the IC7a gain is increased, then R19 being 3.3K largely compensates for this unexpected gain, cancelling
out the problem. Remaining amplitude imbalances can be adjusted out using R27. So the swapped resistors are NO
