I bought an AV Famicom a couple of months ago, and I have played completely through about 3 games on it (2 FC 1 FDS). So I know it was working perfectly before today. Today I fired it up with the FDS connected to it and realized that I had forgotten to plug the controller in. I plugged the controller in and the game froze. At the time I assumed that this was because I had nudged the FDS RAM adapter while holding the back of the unit. I reset it and everything looked fine, but when I hit start to begin the game nothing happened. I tried another game, and similarly, nothing happened. I then swapped controllers and still nothing. It seems like the controller port stopped working. Am I just screwed, or is there some way to fix this? I know newer systems all seem to have fuses, in the controller ports, but I'm guessing this one doesn't (haven't opened it up yet). Do I need to test/repair some mosfet or something? Any help would be great. Thanks.
The AV Famicom has no internal fuses. I doubt if you damaged the joypads but you can test them by plugging them into a NES and they will probably work fine. So that leaves two other possibilities the JIO chip, which if you have messed up then start to look for a new Famicom... the second is (and I haven't got a AV Famicom to check) a diode array, there are three marked DA216 they seem to be connected to the Joypads (but I can't check) you could check them as I believe they are blown. The notch is where pin one starts, there are three pins... Pin 1 - Cathode of diode 1 Pin 2 - Anode of diode 1 and Cathode of diode 2 Pin 3 - Anode of diode 2 1--|<|--2--|<|--3 (like this). A multimeter should tell you if they are blown. If they are then two diodes would do the same job, as long as they are rated 20v or better.
Thank you so much for your reply. Shortly after posting my request for help, life happened and I got sidetracked. I just now got the time to start looking at this again. I have purchased a multimeter (but must admit that I don't have a clue how to use it properly) I have posted a photo of the board out of my AV Famicom below. I see the diode you mentioned on the right next to the controller ports. At least one other person suggested that the JIO chip might be fried (man I hope not), but you are the first to mention the diode. I'm trying to look up how to test a diode, but again, I don't know what kind of diode (if there are kinds) it is or how to test it exactly. If it's a simple process, would you mind explaining it?
I tried to read up on testing diodes, but I think I must have misunderstood something. I took my cheapo digital multimeter out and set it to the setting that looked like a diode symbol in a circuit diagram. The display went to 1. When I touch the two leads together (and hold them still) it will register some 4 digit numbers and then rapidly count down to 000 - I'm guessing that this is measuring resistance, 1 being infinite? (when I touched the leads to a resistor labeled "110" the numbers changed to 109) The next thing I did was locate DA1 DA2 and DA3 on the board pictured above. Since I don't really know what I'm doing, I touched the leads to the diodes in every possible combination I could think of and here are the results: (This assumes I have correctly identified the "notch" and that pin 1 begins on left towards the cart slot on the diodes in the pic above) black lead -> red lead DA1 pin 1 -> pin 2 = 782 pin 2 -> pin 3 = 1434 pin 1 -> pin 3 = 445 DA2 pin 1 -> pin 2 = 838 pin 2 -> pin 3 = 1645 pin 1 -> pin 3 = 445 DA3 pin 1 -> pin 2 = 784 pin 2 -> pin 3 = 1432 pin 1 -> pin 3 = 445 red lead -> black lead DA1 pin 1 -> pin 2 = 905 pin 2 -> pin 3 = 722 pin 1 -> pin 3 = 396 DA2 pin 1 -> pin 2 = 946 pin 2 -> pin 3 = 755 pin 1 -> pin 3 = 396 DA3 pin 1 -> pin 2 = 904 pin 2 -> pin 3 = 724 pin 1 -> pin 3 = 396 This seems somewhat inconclusive to me - but I only have a small understanding of how these components work. From what I've read, I should have gotten a reading of 1 or "open" on some of these or that indicates a blown diode - but could all three of them have blown at once and so consistently? I also read somewhere that I may have to remove these from the board in order to properly test them, and even then replacing them is the only way to know for sure if they were the problem. That leads me to my next question: what kind of diode should I buy to replace these? Just looking through Radio shack's website I found at least three different kinds and I'm not sure which ones would work. I'll happily replace all of them, if someone would be kind enough to point me in the right direction. Again, many thanks for any help you can provide.
Well, my understanding of diodes has expanded somewhat. I now understand the reason you have to remove them from the board to test - because if the current only had the potential to flow in one direction you wouldn't need them in the first place, so testing them on the board will result in false positives because the circuits usually connect elsewhere. I removed all three of the diode arrays from the board and tested them, and there was no leakage when reverse biased. When forward biased, one of them had a slightly higher resistance than the others but I'm not sure I can call that conclusive. Is there any point in replacing these diodes if they seem to check out okay on the meter?
If they're protective diodes, it may be safe to run the unit for a while with them removed. (long enough for you to test the controller port)
Well the system does seem to power up normally with the diodes removed but the controllers still don't work. I guess I'll pick up a pack of random diodes at Radio Shack and see what that does.
Okay, well I've officially ruled out the diodes. I went to radio shack and got some general use diodes, soldered three pairs together so that the meter readings pretty much matched what I got from the original ones that I removed. Still no response from the controllers. It looks like the JIO chip is the most likely culprit (based on what I've been told). Someone told me I could probably build a substitute out of a couple of off-the-shelf '368 chips (basically mimicking the original design that the JIO replaced) but I think that's a bit out of my depth.
lol I was just going to mention that you could replace the JIO chip with two TTL buffer chips (as with the original NES/Famicom design) which would even be more resistant than the JIO chip. It's a Rohm part it seems (BUxxxxx code). It seems that the JIO chip also takes care of the 74LS139 role.
Where did you get your information about the JIO chip? - I literally searched for days trying to find something and came up with zip. I realize that I'm probably asking a lot here, but if you know enough about it to tell me what to buy and how to put it together, I would be very grateful. I understand the principle going on here, just not the specifics. For example, I understand what a TTL buffer chip is supposed to do (at least I think I do) but I wouldn't know how to actually use it to save my life. I tried using a continuity tester to test from the controller ports to pins on the JIO, but I didn't get anything at all. Maybe I did something wrong? I attached one lead to the pin in the controller port, and used the other lead to validate the tester by touching it to the matching pin where the socket is attached to the PCB, then I alternately touched the other end of the tester to ever single pin on the JIO, and the tester never showed a connection. Thanks for all the great advice - I'm really hoping someone can describe in more detail (like part numbers and where to solder what etc...) how to go about making a suitable replacement for the JIO chip, and in the long run, I'm sure it would benefit the community greatly to have that info out there.
The original Famicom schematics are on the interwebs. The original design have an 74LS139 which handles some part of the memory mapping and putting that inside of the JIO sounds smart. You may notice the AV Famicom board has no 74LS139 so the JIO are very likely to be the part doing that function. Otherwise all the chips are identical to the ones used on the original Famicom so bypassing the JIO (using the original Famicom schematics as reference) is the idea. I am sure you will get the chance to learn a lot by working this out, so don't give up ! :thumbsup:
The 139 is used for decoding but that isn't the problem here since games work (it decodes WRAM, the PPU and cartridge); it sounds like a controller I/O is damaged (for input it would be the JIO since it contains the 74368 tri-states used to buffer input). This is very very strange. Controllers are almost totally safe to hotswap (well, it could cause the game to freak out), especially if they're protected by diodes, the input buffers are 74 series (input protection) and the controller is low current CMOS. I'm not sure how the diode arrays are connected because they aren't there on the original Famicom, but if they aren't on the output signals that could be the problem... samson, have you tried a game allowing the 2nd player to start? Or a controller on the expansion port? If either of those work it would indicate P1's input bit is broken. If the controllers are still getting 5V (I imagine they are) but aren't working, an OUTPUT is broken. This could be a problem because on the original Famicom the outputs aren't buffered; if they aren't on the AV FC too (by JIO or protected by a diode), you would have to replace the CPU chip which directly drives the outputs. If you do have to replace the CPU, it's better than replacing the JIO though since it's available in all FC/NTSC NES. I would do more testing before you just buy another AVFC...
I meant he would need to keep the JIO chip in place even if it was what broke down. Nothing more, nothing less... :thumbsup: Samson have you checked the controller cables ? As Calpis said, there's a good chance it's what broke... And I didn't thought of that....
I assume that's what I was doing when I swapped two other controllers with the one I was using. I also recall at the time that I plugged the controllers into a standard NES and they seemed to work fine. I thought of that too, but I only own a handful of titles for the Famicom and none of them allow player 2 to start or interact before the game is started. I imagine they're common but none come to mind. Do you have any examples of games that do this off the top of your head? Also, I don't have any controllers that would work in the expansion port - I could buy one, I suppose, but without another Famicom to test with I would have no way to know that the controller was otherwise working. It's still worth a shot, though. Anybody know where I could pick one of these up on the cheap? They seem a little pricey on Ebay. So to test this would I touch my meter to certain pins (1 and 4 maybe?) on the controller port while the system is running to see if I get 5V? If I do, would the next logical step be replacing the CPU? Or should I do more testing first (and if so, what?) I do have a NES that could be a donor for this...
