80s Philco-branded Philips 13" - Very dark screen

[YamahaFreak]

Adjusting the color control has no noticeable effect on brightness. I pored over the entire board and could not locate a service switch anywhere, which actually surprised me, given I usually do find one. All other controls work as they should, just...a really dark picture. Menu is fine, as is blue screen brightness while auto channel searching.

EDIT: It's doing something else I hadn't noticed before. Almost like clockwork every 7-8 seconds, the image will get slightly fuzzy (like someone tuning away from the center of the channel on a knob tuner) and then 'snap' back into focus. Weird. I thought maybe it was some outside interference but nothing I can think of is running nearby.