To discharge the capacitors, just short the 2 terminals with a resistor. Don't have one? Just pick one up when you order your replacement capacitors. Don't use a very small resistor or it might spark like a short circuit. Use a larger one (I'd say at least 1k). You can even use a really large one, like a 1M Ω resistor but the larger the resistor, the longer it takes to discharge since current will drain slower. If unsure whether its fully discharged, just check with a voltmeter between the 2 cap terminals. It may never go down to zero, but you just want to make sure it's not 90v or some other high voltage, and you are probably safe to work on it if it's just a couple volts. I forget about the G9000 but you might not be able to find suitable replacements for the large filter capacitors, since not only are the purpose important, but also the appearance of the original caps. Modern capacitors are typically smaller than vintage equivalents of the same capacitance. This characteristic allows an opportunity to "rebuild" the original capacitors by "stuffing" them caps after gutting. Whole tutorials or articles have been written on how they did it, so just google about that, if it's something you might be interested in. But first check if replacements are available.
Do (1) at a time, and always note the orientation of the polarity. You don't think you'll forget but I'm telling you after 80 caps, it's easy to forget immediately after you pull it. For this reason, before I begin, I simply make a mark with sharpie on all the caps at the N (or whatever you wish to use as reference) position. After you pull, if you suddenly realize you already forgot, then look at the mark on the cap. Since all the caps were marked at N position, then you'll know which way it was oriented before you pulled it. Then before you start on the next one, clear the bench of all used caps to avoid confusion. Unlike a boombox, these receivers use high voltage and if improperly rewired or component orientation not observed, you may literally see smoke and cause substantial damage.
The protection mode issue is problematic, hopefully your cap replacement helps it, but if it doesn't, then you may need the assistance of a tech. There are people all over ebay offering repair services on these classic receivers. I'm not recommending any in particular, or even using ebay as a source at all. But I will say that usually the people that specifically offers a G-9000 rebuild service are usually very familiar with that particular receiver, which your local shop might not be. Or you can check out the guys on some of the hifi forums. I can recommend user Pacific Stereo over at tapeheads.net, as I know he does fantastic work on the top end Pioneer receivers. You can contact him over there and tell him Norm sent you if you decide you wish to investigate that path (he owns the forum over there). Forget about sending it to me though, these days, I can't even lift 1/2 a receiver much less a full one.
