Re: QCX TROUBLESHOOTING


Syd
 

The biases on C43 through C46 should all be very close to each other since that is where the I and Q pulses are integrated/filtered and all the filter circuits are identical.  So compare all 4 of the caps to resistor (R5, R6, R8 & R9) junctions with a DVM. If one these is off make sure there is a ground at the gnd end of the cap and then check the filter resistance value.  You could also ohm out each cap/res junction to ground just in case some is messing up the  paths from the Quad chip. Make sure the caps all have the same code.

Actually looking at the schematic you should be able to pretty accurately measure all the resistors in-circuit in all the OPAMPS! I have found out the hard way that the pots can give some strange problems if any one of them are at the shorted out end of range, so make sure to  measure them to make sure they are not at the end of range.
wt1v

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