H7202KA power supply

Hi Guys, I managed to get the two DEC cabinets into the attic. Turned out I could just handle them by myself, without removing any rivets (emphasis on "just" as in "barely"). I've now got some of the Unibus PDP's in my hobby room (a /05, a /24 and a /84), so I figured I'd start with the latest model of the three.The 11/84 has a H7202KA power supply (H7200 + H7211 + H7213). All voltages look ok with a multimeter, but on my scope, the +5V VBB supply looks like a sick puppy. It looks like a sawtooth, with a period of 170 msec (ca. 6 Hz), and an amplitude of about 400 mV. Add to this a peak of 300 mV for 30 msec at the beginning, and a spike of -500 mV at the end, and there's a peak-to-peak difference of 1.2 volts. There's also some random spikes. In the end, the waveform looks like this: 5.5v -> |-_ |-_ | | | | | |__ | |__ | --__ | | --_| 5.0v -> | --|_ | --__ | | --__ | --__ | | --__ | | --__ | | || | || 4.5v -> / |/ |/ | | |----------------------| 170 msec The measurements were taken with the power distribution board and minimum load module plugged in; I don't want to plug any other modules in while the power looks like this. Is there any documentation available on this power supply? Or, does anyone have an idea as to what's going on here? The 6 Hz frequency strikes me as odd... Cheers, Camiel.