OK, I guess we need to check the -15V and +5V regulators on the LVPS.
We have to fix the +5V regulator first because the +5V rail voltage is used by the -15V regulator.
The 5V regulator is a standard linear series regulator using Q5 (off-board) as the pass transistor, with U2 as the controller.
Can you measure the following voltages with the scope powered up and everything connected as normal. When measuring U2 pin voltages, be careful that the probe doesn't slip and short two pins together. If possible, measure the U2 pin voltages on the underside of the PCB. Measure relative to 0V except where stated.
1. Across R30. Should be less than 0.6V. R30 is a "current sense" resistor, connected in series with the load, so the load current can be calculated using Ohm's Law: I = V / R where I is current in amps; V is voltage across R30 in volts, and R is the resistance of R30, in ohms, which is 0.82.
So when you've measured the voltage across R30, divide that value by 0.82 and the result will be the load current in amps.
2. The +5V rail test point.
3. Q5 (off-board) collector. Should be between +7V and +10V roughly.
4. U2 pins 7 and 8. Should both be about +15V (they come from the +15V rail).
5. U2 pin 3. Should be between +4.5V and +5.5V. This pin sets the +5V rail voltage.
6. U2 pin 2. This is the feedback from the +5V rail that U2 uses to tell when the +5V rail voltage is right.
7. U2 pin 6. This is the output from U2 that controls Q5. It should be about 0.7V higher than the +5V test point voltage.
With those numbers, I should be able to figure out the problem with the +5V regulator.
It seems reasonably likely that U2 is faulty. This is a µA723H or LM723H regulator. U1 and U3 are the same.
The ones used on that board are in a 10-pin metal can package, indicated by the "H" suffix on the part number, which is still available from Texas Instruments at
http://www.digikey.com/product-detail/en/LM723H/NOPB/LM723H/NOPB-ND/148205 for USD 8.45. The DIP version (
http://www.digikey.com/product-detail/en/UA723CN/296-11104-5-ND/382232) is under USD 1.00 but would require an adapter made from a socket and some wires.
If U2 turns out to be faulty, you might want to buy one more in case you need to replace U3 in the -15V regulator as well.
What is the status of the HVPS now? Is it running?