The right channel of the RCA output went out on me today, and I tried opening it up to have a look, and I have no clue what I'm doing. I don't want to risk damaging it. I've been digging through threads, and I haven't found anything helpful.

Flip it over, remove the screws with a crosshead screwdriver, pull the volume and control knobs up and off, lift faceplate off. The motherboard is connected by wires to the unit by wires so don't yank on that too much. The rca deal is right there when you open it so if you can solder it will be simple to replace.

I attached a few pictures of my SP 303 opened up. I don't really know what I'm looking at, so I was hoping maybe one of you guys might be able to see something that I'm not seeing.

In short, the right channel of the RCA input went out around the time I originally posted this thread. I've been busy however and haven't had the time to mess with it, up until now. If anyone has some suggestions on what I can do about it, perhaps a place to have it repaired for under $50, that'd be great!

try a search on this section, we posted something very similair about the RCAs

Just buy new RCA outputs, unsolder the old ones and solder the new one. Its pretty straight forward, no need to work on the whole circuitry.

How about the headphone out? Does that work on both channels or the right channel is missing too?

Yeah, the output works just fine, both the RCA output and the headphone out. It's only the RCA input that I'm having a problem with.

If I were to replace the RCA, where would I be able to acquire a new RCA inputs? Also, how much would it cost either to fix it myself, or to have it repaired by someone else?

Example of rca input being replaced on a circuit board.
https://www.youtube.com/watch?v=F028FG6Ynok

Rca input
http://www.ebay.com/itm/Dual-Input-RCA-Jack-for-Car-Audio-Amplifier-Amp-Repair-FREE-SHIPPING-FROM-USA-/182476938420

or

http://www.ebay.com/itm/Quad-Input-RCA-Jack-for-Car-Audio-Amplifier-Amp-Repair-FREE-SHIPPING-FROM-USA-/182476948798

Not too difficult, but requires a little bit of a steady hand. Just find a junk circuit board from some old broken electronics and practice unsoldering and resoldering things to it. The main thing to avoid is letting two solder points next to each other touch, this will cause the input to short out and damage the unit. I recommend some reading on electrical theory, the principals involved dictate how sounds are capture and reproduced with electronic devices, this will open a door to understanding how phase/polarity affects sounds reproduced through stereo sound systems. Stuff like mid/side listening and new creative ways to eq stereo 2-tracks without stems, which is what we find in vinyl records. Then you will start notice how people isolate certain sounds in mixed and mastered stereo sources so precisley. Anyone can make a beat but it's how you treat the sound that adds your flavor or accomplishes your goal. Sorry for the rant, but I haven't said shit on here in a while.

I decided after a year of it not working, I'd try and repair the RCA jack myself.

However, the right input channel still isn't receiving audio. It's not the cable, I've checked. Is there something in here that maybe I'm not seeing? I've also cleaned around the contacts with rubbing alcohol.

Oh and a side note, the metal pad that was stuck on the contact point came off (the one right of center) which I'm guessing may be the reason I'm not getting audio in that channel? If so, how would I fix it? I think I'm referring to a "copper pad". I put it back on and put solder on top of it, but I don't know if that changes anything.

Anybody have any ideas of what's wrong with my 303?

Is it output or input?
Did you try to record stereo from Mic input (don't knouw, if Mic in is stereo?)
if problem is on Input. If this works, problem is in RCA input.
If the problem is on Output and you tried Headphone output and it works fine, there Is problem with RCA output.
anyway
if Mic input and Headphone output works and RCAs are OK, there is a problem in electronic around RCAs
This could be a little tricky to find a damage and repair it by yourself...
but the damage should be just one little resistor or capacitor blown.

OR
there could be another problem - Mic input turns off RCA's input. Maybe It's blocked on it's possition and causes one of RCAs input is permanently turned off

Audio comes through on the mic input, which is mono. It is the RCA input that I'm referring to. One channel lets audio through, the other does not.

What would that type of repair entail?

hm.
you should find cheap service guy...

anyway you could check, where is audio defected
check the service manual page 30
get some cheap PC speakers (with amplifier in it), connect some audio from cheap MP3 player or walkman (there is always chance you blow your source of audio or your speakers by doing this ...) to both RCAs, play audio.
connect sleeve of PC speakers connector to ground of 303 (eg. sleeve of RCA), connect tip of PC speakers to wire, try with wire's other end some points on 303's PCB - there should be audio playing from your speakers
check tip of RCA's in, if audio is playing - RCA's are OK, than you could go by traces of 303 according to circuit diagram in service manual.

Mic In goes together with Line In to IC3

If you could sample from mic in and audio is in both channels, there is problem with Line In BEFORE IC3

Check in audio is playing on R135
Check if audio is playing on R144
there is probably problem around IC2 or In it (it's Operation amplifier)

Anyway if you could locate defected component, you wouldn't be able to change it probably...

I had the same problem. Sent it to Roland and their technician did it for me for a fee. He was quite surprised to see a 303 in real life lol.

Does anyone have the service manual for the 303 they could share?