Hi, recently got broken Agilent E3647A power supply, voltage readings and setting weren't working, turns out a lot of precision resistors(green ones) were open, double the value, or 5%+ off, replaced 10 of them and it works fine(needs calibration tho).
But then I discovered that on CH1, OVP function trips too early, when output is set over 36V where OVP is set to default 66V, on CH2 it works fine.
Started probing out, and found that resistors are fine, op-amps are fine but output on U31(analog multiplexer) for OVP function for CH1 shows about half the voltage.
To be precise, when OVP is set to default 66V on both channels, then U31: pin4=113mV(working CH2) pin15=76mV(faulty CH1).
So I supect this multiplexer to be faulty, but I'm not sure as I don't really understand how they are using one DAC to control multiple functions, are they switching dac+multiplexer really quickly?
Also I wouldn't suspect the DAC to be faulty because then all voltage/amperage settings wouldn't work properly as well, right?
Is there a way to somehow measure this multiplexer?
Part of the schematic in attachments, manual and all schemtics here:
http://ridl.cfd.rit.edu/products/manuals/Agilent/power%20supplies/E3646AE2.pdf