diagnosing an Intel Series II MDS monitor failure

The error amplifier of the 723 has both inputs brought out, the reference is not connected to it [1]. So for 5V (or voltages under the reference voltage) you can link the sense wire directly to the +ve input of the error amplifier and a divided down refence to the -ve input. The only practcal advantage of the lower reference is that you can run the chip with a lower supply voltage I guess [1] It is not at all uncommon in systems with multiple 723s to use the reference of only one of them, feeding the error amplifiers of all the ICs. All PSU outputs should then track together. Or in some cases to ignore the reference altogether and, for example tie one input of the error amplifier to ground and the other to a potential divider between the output of that section (configured as a -ve regulator) and a positive supply rail. This then gives you supplies balanced about the ground rail. HP98x0 machines are one place this turns up, there are many others. Possibly, although for most applications this would not be important. -tony