Matt
Got your PM and for the benefit of the other members, I will attempt to give you pointers. Unfortunately, I am not at home and don't have the manual handy to reference exact details on parts.
As you had guessed, the slow blow fuse blew for a reason, and you shouldn't just replace it. It would do more damage if the new fuse doesn't blow...
The first area of troubleshooting would be to mark the cards from the bottom rack and remove them all. Then disconnect the Molex connector that feeds DC outputs from voltage regulator board to the Basis Board. I would visually inspect for an axial filter cap for 5.6VDC in the voltage regulator board that is mounted on the left side metal frame as you look at the machine from the back and the basis board where the cards were plugged in before. If you see the dreaded yellow/gold colored Frako type caps, I would replace them first before you go any further.
There's a small chance one of the large can bolt mounted type cap could be bad but it is less likely (unless your machine is the typical eBay sourced A810 had been resting for the last thirty years).
After removing the Molex output connector from the DC Regulator board (or Studer Stabilizer), you put the replacement fuse and power up the machine. Be careful to measure the output voltages from the board pin outs. Check the manual for proper output voltage spec. My guess is that the Stabilizer would be good in supplying the +24V, +5.6V, and +/- 15VDC. If not, I would go back to checking out the input voltages from the power transformer/rectifier/bolt mounted filter caps to the Stabilizer. If input supply voltages are good, then you know you have an issue with the Stabilizer board.
Otherwise, if you get good output voltages from the Molex connector pins from the Stabilizer board, the most likely cause for your trouble would be that you have shorted filter cap(s) in the following boards:
1) basis board - again if they are yellowish Frako type with known 100% failure rate, you would need to replace all of them anyway.
2) LED control panel - if you had Frako caps elsewhere, you are sure to have one there as well. Replace it. If it is shorted, it will blow the SB fuse.
3) Although not related, you should also replace two axial filter caps under the headblock for +/-15DC supplies to the head preamp.
After recapping, you should power up and measure the voltages from the back of the machine at the top section of the basis board's solder side that is marked with proper voltage numbers. After verifying you have good voltages at the back of the Basis Machine solder side, I would power down and insert only the transport cards first. Measure the voltages again at the back of the Basis board. If good, then insert one channel of audio cards and check again...and next channel, etc.
You should be good to go by then.
Hope it helps. Good hunting.
Ki