By "Not powering up" do you mean not spinning? If the drive is not spinning with just power applied it could be two things assuming that power is reaching the HD. First old drives sometimes fail to start due to the heads sticking to the disks. Tapping the drive against the palm of your hand while power is applied will sometimes free them. It is a temporary fix however and the data should be copied if it is needed.
The second most likely fault is a bad logic board. Although it is possible that the motor is faulty, it is rare. Swapping out a logic board is a fix for a faulty board, but you need to find one just like the old one. Sometimes it requires the same ROM series rather than just the model number of the HD. For what it is worth, many times the fault on the PWBs are open chokes. If you find one it is easy to replace it with one from a scrap PWB.
As for test equipment, I would think that a good DVM would be the only tool required for trouble shooting the PWBs. It is alway nice to have more equipment, but since many ICs are custom made, it is highly unlikely that a replacement is readily available. At least that has been my experience.