Hey there peoples. I'm very new to electronic repair (like looking up what the symbols on my multimeter mean new). I've been meaning to learn how to solder and everything for a while and decided to use my old broken game systems as practice. If I've screwed anything, it's not a big deal as I've been totally prepared for beginner's failure. I was able to fix the NES which was thrilling but the SNES has made me feel pretty lost. So, a few years ago I had cleaned the SNES with alcohol and (like a total nub) not completely let it dry. When I turned it on, there was a tiny pop and no power. I seem to remember the pop happening around the switch but I left it at that since I had no tools or knowledge to go further with it. So, I've tested the fuse for continuity and it seems fine. The AC adapter is also putting out the correct voltage. I don't see any corrosion or burn marks anywhere. Here's where I'm not really sure what I'm doing so there may be some obvious mistakes: I checked for continuity in the power switch using the + and - wire connections under the tiny board where the black switch is. No continuity. Tried bypassing the power switch but got no results which led to me trying to check for continuity in the pins where the power switch connects to the motherboard (right above the fuse). Nothing there either. I've basically just been awkwardly cobbling together info from different threads and tutorials. I had a horrible STEM education in grade school and no interest in pursuing such things on my own, so now it's like dyslexia looking at this stuff sometimes. Any friendly advice or brutal chew outs (peppered with clues to improvement) would be much appreciated.
I thought I had tested the input correctly earlier and didn't get any output at all. Wasn't sure if getting no output was the result of there being no power. Just re-watched a tutorial (just to be safe) on testing the 7806 and now am getting nothing for input or output, so I guess that means it could be a bad voltage regulator. I was sure it had an input reading earlier so I hope something didn't happen in the mean-time and replacing the regulator will merely fix an additional problem I created.
If you have no input voltage it means the regulator is not receiving current. In other words, the continuity is broken somewhere before that. Could be the hot line but could be the ground too (less likely but still possible ). IIRC the Switch is before the regulator so check that out, just follow continuity from the power adapter input until you find where is the break.
Okay, so there's continuity from the plug to only the right two connection points of T1, marked TDK ZJYS-2 J (which looks to me to be the first point of contact on the board). Nothing for the left two. If the common mode choke was bad, wouldn't continuity be absent on all 4 connection points? Update 8/10/14: So I've been looking at the power input section of the SNES schematic (kindly cropped for me by KrisBlueNZ over at electronicspoints.com) So I'm a bit confused as to what differentiates J1 from the DC Jack. I know that the symbol at J1 is for a jack, but cannot find info on what that long rectangle with the circle means above DC Jack, though obviously the title DC Jack means it's a jack also I guess. Also it's surprising to me that the cap at C70 comes before T1 since it's literally on the other side of the mobo. Again, though, there's continuity to C70 from the power jack and only half of T1. Should I just go ahead and replace T1? I'm really not seeing what else could be the problem. No broken traces that I can see.
Bumping for the update in the above reply I posted, and also because I found out even more: So after being pretty confused by the fact that the schematic says C70 (which is on the other side of the mobo from T1) is the first thing to get power, I found a project specifically called "legible SNES schematics" over at NesDev.com Turns out that is not C70 but in fact C30. Well this is still very confusing to me. If C30 is what bridges DC Jack to everything else, how can DC Jack have continuity with only one side of both C30 and C31? It would have to go through the side that I'm not seeing continuity for to get there. There's obviously something I'm misunderstanding or not measuring correctly.
C30 and C31 are decoupling cap, positive side should be connected to + side of DC jack, and the other side to the Negative side of DC jack.
I think what's happening is that the DC resistance of the common mode choke is so low that your meter is taking it as a short circuit. Since power supply circuits are generally low impedance, I also think you will get better results by applying power to the circuit and then using the meter (in DC Volts mode) to find out where it stops.
Thanks guys, that helps a lot. Should have figured that polarity played into it. Update: So if I'm getting +14v on the anode, I should read around -14v for the cathode correct? From what I'm reading it seems the diode just redirects the current while blocking it from going other directions so I shouldn't get a drop in voltage.
There will be a small voltage drop - typical silicon diodes are about 600mV - judging from the schematic, this specific diode is a Schottky barrier type, so the voltage drop will be lower than that - say 200mV - 450mV depending on the If through the diode. If you are getting 14V (referenced to ground) on the anode, you would expect to see 13.5V to 13.8V (also referenced to ground) on the cathode. If that is coming from a standard SNES PSU, it also very strongly suggests that there is no current being drawn at all.
What? Stick the negative lead on a ground point and probe known positive points. Simple. And J1 IS the DC jack.
K, so the diode was bad so I replaced it with a 1n4001 micromini diode which worked great. The fuse blew promptly after that. Went ahead and soldered a fuse holder and put in a glass 1.5a fuse. Now I have power! So thanks for the help. I'm getting better at understanding the mutlimeter and diagnosing the board little by little. I'm a hands on learner so thanks for the patience, the feedback helps solidify concepts in my brain even if they are extremely simple to begin with. Right now I'm having trouble with selectively garbled graphics. A cut-scene and menu will be perfect but then the level will be jacked up. There's also something weird going on with the relationship with the controller. Mario Kart works fine in 1 player mode unless I press the R button which crashes the game to a crazy flashing blue screen. Trying to find dirty contacts or corrosion that I might have missed. The pin connector seems squeaky clean, but the games are dirty as all get out. However, cleaning them thoroughly doesn't change anything. I'll keep exploring some options. Thanks again.
when you cleaned that system years ago with alcohol, did you take it apart or just cleaned it through the dust flap? I think one of the chip in the console might be damaged.
I took it apart. It wouldn't surprise me if one of the chips was damaged regardless, but if I remember correctly this kind of problem is what I was trying to fix by cleaning it back then. I think I had started with cleaning the game, then cleaning the pins through the dust flap (so I guess I did clean it through the the dust flap but nothing worse happened or got better), and then finally taking the whole thing apart and trying to clean it that way. Right now I'm looking at this thread: http://www.assemblergames.com/forums/showthread.php?47286-More-SNES-mainboard-repair! Calpis says, "Bad chips are possible, but unlikely. Far more likely is a open connection." I'll do some reading and see if I can follow his suggestions. If I end up needing to buy a new VRAM chip or something, I probably will. I've spent more money on this project than just buying another SNES (though that includes the soldering gun and multimeter which is more than an investment just into the SNES), but it'll be good practice.
I think the 1N4001 has a max current rating of 1A. The diode will blow before the fuse next time. I would replace it with a 1N4002 (last digit is current rating). This way the fuse will blow first, easier to replace.
Had a similar problem just a few days ago. The diode D1 was damaged. At the input I had 9V, at the output 1.3V which is the input of the voltage regulator. So I replaced the diode (btw. it is a sot89 package) as everthing was fine again. Once I desoldered the original diode, the cathode came off the housing, which caused a lose connection. Now the SNES runs and runs and runs... Have a try
For 1N4001-1N4007, the last digit is the voltage rating, not the current. They are all 1A devices. The equivalent 1.5A series is1N5391 to 1N5399 - also with increases in the last digit indicating increases in operating voltage.
