For the one with the missing -23v rail:
According to page 27 of the schematic, there's really not much between the output of the -23v rail and the source transformer.
The only component between the transformer and the -23v output is a 300 ohm 10W resistor. There are also three capacitors to ground (C8, C18 and C37), and finally a rectifier diode on ground ( D28 ). With so few components, there's very little that could be wrong on this rail. The first two things I'd suspect are the 300 ohm 10W resistor being open, or the rectifier diode being shorted. If those two components turned out OK, I'd then check the three capacitors to see if they were either shorted, or are electrically leaky or have high ESR.
If all of those components test OK, then it would mean unfortunately the winding on the transformer is open. There's really nothing you could do to fix that, unless you have experience rewinding multitap switching transformers. You can test for this with the power supply off and make sure the line capacitors are discharged. Use ohms mode on your multimeter and see if you get a reading between the -23v tap and ground. If you get nothing, then the winding is open.
If the winding did blow open, then there's a pretty serious fault somewhere in the terminal, I would check resistance to ground on the -23v rail from the power supply connector on the edge connector without the power supply installed and see if you get a very low reading or near 0 ohms, indicating a short.
For the one that blows fuses:
Blowing fuses is almost always a fault with the primary side of the power supply. I would check the bridge rectifier first and see if one of the diodes is shorted (D16, D17, D18 and D37). In diode mode with a multimeter, you should get a voltage drop between 0.5-0.8v when measuring from the cathode (-) to the anode (+) and OL or nothing when reversing the test leads. If you get continuity in both directions, or a dead short, then the diode is bad and needs to be replaced. You may have to lift a leg of the diode to do a proper test, because other components in circuit with it can give you erroneous readings.
The next thing I'd check are the line capacitors (C9 and C14), you'll need a capacitor tester for this. I'd recommend one of the cheapy Ebay ones because they're good enough for stuff like this.
https://www.ebay.com/itm/353404276114
For capacitance, you should get within +/- 20% of the capacitor rating, but obviously the closer to the rated value the better. If you get a reading too low, it generally means that the capacitor has dried up. If you get a reading too high, it usually means that the capacitor has become electrically leaky. In either case, it needs to be replaced. When a capacitor gets real bad, it can short or go open circuit, the former of which can cause the fuse to blow. I have had shorted line capacitors in power supplies before and they do cause headaches.
The last major culprit are the 100k ohm 1W resistors (R19 and R20). These can drift in value over time, short or go open circuit. If the former two cases happen, they can cause the fuse to blow. It would generally be pretty obvious if the resistors were a problem because they'll cause the PCB under them to discolor.
If none of these are the problem, I'd start checking the switching circuitry feeding the second tap on the transformer on the primary side, which is on the upper left of page 27, under all of the components I just mentioned. There are a lot of diodes and a few transistors here that should be checked, along with the couple of resistors.
