I'm working on a NF that has had multiple problems with the switches and matrix. I have it down to one problem and that is Row 6 is not working. I've replaced the LM339 and checked for continuity. I've checked resistors diodes and even went over the solders just to eliminate it. It is definitely on the board as I pulled the connecters off and shorted the pins. I had a bad LM339 on the opto board that I replaced. That fixed my one problem although I now have a flickering switch at #36 which is not used. It might be one of the traces got beat up and is not making good contact. I'll check that after I find this problem. But, the switch is not used so I don't think it would create a problem. I did unplug the opto board just to make sure it wasn't creating a problem and it isn't. I think this pin may be cursed. It's been in my shop more than it has been on the street. I'll tell the story below and you can read it if you want. I appreciate any help getting this thing up and going again.

This is going back quite a few years. There was this woman who I loved very deeply. A little too deeply. When you love a woman that much they usually break your heart and that was what happened here. I knew it was over but she was too much of a coward to pull the trigger. So, I pulled the trigger and ended it. We were very calm with one another. I play in a band and I told her to please just let me alone for a couple of months. I told her it would just hurt too much to see her. I said in a few months do whatever you want to do, just give me that time to heal. I had a diamond tennis bracelet that I had bought for her in my safe. I told her I would see that she got it in the future when I could handle seeing her. We had a gig that weekend and wouldn't you know that bitch came walking through the door with another man. I was furious! I went up to her and tried to get her to leave but she wouldn't. After the weekend I called a friend who had his wife's anniversary coming up. I told him I would trade him the tennis bracelet for a No Fear pinball machine he had. He agreed and the trade was done. I took it to a bar right by where this woman worked. Several months later she called me and we talked. She asked about her bracelet and I told her what I did and where she play the pinball machine that I traded it for. Since that time the pin has spent MUCH more time in my shop than on the street. That's why I think it may be cursed. But, it was still worth it. After that there was only one thing left to do. So, I wrote a song about it and we shot a video with the band:

https://www.youtube.com/watch?list=FLRFybcc66YxdNLFFVfxdVuA&v=4AP4SIHOU-g&feature=player_detailpage

I appreciate the reply. I have it down to a board problem. But, I still did check the spinner and diode which are good. I pulled one leg out of d6 & d12 and tested them and both test good. J205 are the direct switches. But, out of curiosity I put it into switch test and removed J205 and J212 and I still don't have row 6. U19 is a good call. I have replaced it twice already just to rule out the possibility of a bad one from factory. Normally these problems aren't that hard to fix.... but this one is quite the puzzle at this point.

Thanks terryb. I don't have a logic probe but I do have an O-scope. I will check through this and check back.

LOL! If I had a nickle for every time I heard that live. "Slayer" is another thing people tend to yell out a lot.

J205 are the direct switches but I got what you were saying. Here is what I came up with according to your suggested test terryb:

U19 pin 8=5vdc
U19 pin 9=12vdc (no jumper)
U19 pin 9 with jumper from J208(row) pin 7 to J207(column) pin 1=pulse signal
U19 pin 14=5vdc (no jumper)
U19 pin 14 with jumper (same as above) =pulse signal

There are three 74240's on the board. I just took a reading on all of them. You can use whichever one you need. I was getting a double line which I am just going to call a pulse. It is just probably faster than my scope could read. In any event here is what I came up with:

Pin 4 no jumper:
U15=5vdc
U13=5vdc
U11= 0vdc

Pin 4 with jumper:
U15=5vdc
U13=pulse signal
U11= 0vdc

Pin 16 no jumper:
U15=pulse signal
U13=0vdc
U11=0vdc

Pin 16 with jumper:
U5=0vdc
U13=0vdc
U11=pulse signal

I pulled U13 out some time ago and tested it with a TTL tester on my computer. It tested good so I put a socket in and put it back in the machine. But, I put a new one in and sure enough that was the problem. I guess I can't trust that TTL tester anymore. I can't thank you enough for all your help terryb. I truly appreciate it! Since you walked me through this I have a far greater understanding of how to test through the circuit. Thanks again I really appreciate your time.