Remember that it might still read +5v on your meter if it was a fast changing logic signal, as the meter wouldn't be fast enough to actually keep up with the changes.
Is there already a regulator in a SK5, i don't remember? If there is, and its a full size one then it should be able to supply up to an amp, which is way more than anything you could build and wire in could possibly pull, unless theres a bad short somewhere. If there is a regulator then source your 5v from its output pin, and source your ground from its ground pin. Alternatively you could use the ground and +ve rail of a nearby logic chip, which is probably running on 5v.
If the SK5 has one of those TO92 transistor case regulators like your 78L05, then i think they can only supply 100ma, which might prove a problem. I assume the PSU you're using is up to the job?
Try running the SK5 on 9v, it won't hurt it.