Working on old Reel machines

[peopleperson]

Hey, does anyone know where there might be some information on servicing older model reel to reel machines? I have two really nice Roberts decks that have particularly good sounding preamp modules in them. It seems that only one module in each of them seems to work (even though I've had both working at one time), and I'd like to know how to possibly work on them. I've read a few things here and there that point to putting new capacitors in old gear as they're one of the parts that will go bad, but I'd like more info if possible. Also what about taking modules out of decks, building a seperate power supply for them and taking them out? Any clues?