Old electronics can be a good source of various precious metals, like gold, which is used the most. The problem lies in the fact that it can be rather difficult to extract these metals from circuit boards, pins and all the other places that hold them. You could scrape them down with a tool, melt it down, but all of these methods cause loss of the the metal and they end up containing impurities. Because of that a different method of extracting precious metals from electronics has be introduced, reversed electroplating.
Before you do anything at all, it's important to point out how complicated and dangerous the process of precious metal extraction from scrap electronics really is. In order for you to successfully remove metals you would need to go through two separate processes, extraction and purification. Both of these imply the use of dangerous chemicals which can be rather harmful to your health, because of that you should wear at all times, rubber gloves, protective apron and a breathing mask. If you feel like you won't be up to it, then don't do it at all, because you could end up inhaling dangerous chemicals, pouring acid on your skin that will burn your skin or both.
Besides the health risk, which this type of a hobby certainly is, there's also the question of how profitable the gold extraction from electronics scrap really is. In order to do the process you would need a whole bunch of various chemicals which might not be easy to find and they would also cost money, the search for the chemicals would also cost you money. This is only for the process of gold removal from the plated areas of the electronics, you also need chemicals for gold purification, since it isn't necessary for the gold to be pure. Let's not forget that you would also have to pay for various other knick knacks, which depending on where you're at could amount to a decent sum of money.
So, we already have expenses and we haven't even reached the part of the equation which will be the most expensive, finding electronics. Unless you are a repair person, there's no reason for you to have a lot of old electronics lying around, is there? And if you think that it doesn't take a lot of circuit boards to earn cash, keep in mind that even in the best circumstances, someone with a lot of experiences doing the extraction in under bestest of conditions, you'll only recover somewhere around 1 gram of gold per PC motherboard. In order to achieve a more substantial profit you would need to find a large amount of electronics, and since a lot of people is doing this, you would need to spend a lot of time searching and spending money on transportation fees, storage and so on.
When you add all that up, you reach numbers that give you a marginal profit, if any at all. Because of that, it becomes questionable if doing something like this be profitable? Well in most cases it wouldn't, so what then should you do if you already, for some reason have a lot of electronic boards and whatnot? Best thing would be to drive it all to scrap metal recycling center near you, ask around for one, and they will probably take your scrap in and pay you a certain fee. These kind of companies have their own rules on what kind of materials are allowed, for example you will probably need to strip down the contacts and pins yourself, remove any plastic, but it's best to ask them and see where stand. By doing this, you save yourself a lot of trouble and you turn a profit, hopefully.