Alright here you go....read this as well but note it's rev a so some values (DC and component) will be different.
http://www.groupdiy.com/index.php?topic=29981.msg615080#msg615080
Print off the rev D schematic from the MNATs site. Now go to the rev A schematic and write in the pad numbers from there on to your Rev D schematic...20,21,18 and so on.
Now here is one of your issues....you have no DC voltage at pad 21. Here is how you get that voltage. Look at your schematic, R64 connects to your -10V rail and then to pad 20. From here is runs up to the ratio board and feeds the R63, R62, R61, R58 divider network and back down to the Qbias wiper where it connects to ground closing the circuit. Looking at the schem R64 is 1.5K and the rest of the R in the chain are like 2K all together. So you'll a sizable drop across R64. Rail on one side (-10V) and something like -6V on the other. If you don't at least have this with PAD 20 disconnected you have a main board issue at R64. Edit: With pad 20 disconnected you'll have no path to ground...so no voltage drop accross this R. Just make sure you have that side of the R64 going to the raio PCB pad 20. [End edit] Now this 6V gets connected to that R network with pad 20. Now if you follow those resistors in order you should see a stepped drop -6V -> -4V -> -3.2V -> -2V (real roughly) until you get to the other side of R58 where it should be near fairly low, like -1V.
Now the switch just taps off those stepped voltages 6V -> -4V -> -3.2V -> -2V and feeds them to pad 21.
You've got basically no voltage anywhere in that chain I just described. If you have -6V or whatever on the on side of R64 and not at pad 20 on the ratio, then you have wiring issues. Likely it's miss wired, which would also help explain your voltage sag.
Good luck.
