(Topic ID: 193902)

Sinbad replay not working

By royball

4 years ago



Topic Stats

  • 6 posts
  • 2 Pinsiders participating
  • Latest reply 4 years ago by royball
  • Topic is favorited by 1 Pinsider

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#1 4 years ago

Rebuilt a Sinbad four years ago. New Ni-Wumpf board, power supply and re-pinned. Worked well for a few years. Suddenly when restarting after a shutdown the replay button would not work. Board starts stars up with high score and rings chimes. Replaced the 74156 IC and worked again for a while. Now replacing the IC doesn't correct the problem. I am trying to find a short in the matrix circuits with no success so far. A logic probe shows a high on the return matrix and pulses on all the strobes except the tilt switch strobe. Any ideas are welcome.

#2 4 years ago

You would have to be pressing the start button while probing the proper switch return to see a pulse on your logic probe. Otherwise, with all switches open, there would be no activity on any if the return lines.

#3 4 years ago
Quoted from CactusJack:

You would have to be pressing the start button while probing the proper switch return to see a pulse on your logic probe. Otherwise, with all switches open, there would be no activity on any if the return lines.

Thanks for the reply, I don't really understand the strobe/pulse logic. What I did was disconnect the J6 connector and touch the logic probe to the board contacts. I was trying to see if the chip was operating. I did power off when I disconnected the connector. Maybe my question should be, Is the return line supposed to be high or low with the switch open?
As you said the switch was open.

#4 4 years ago

Sorry for the late reply.

Yes, the returns have a pull up resistor so they would normally be sitting at a high as long as all the switches are open OR the switch matrix connectors are unplugged.

If you found one low in this condition, it would indicate a damaged input chip. And more than likely, would show every switch on that return being reported as closed.

As to the strobes, they are continuously pulsing as only one strobe is "ON" at any point in time. The CPU turns one strobe on (low), and then reads ALL the returns to see if there are any closures (inputs low). If a switch is closed, it allows the low strobe to drive the Return input low (instead of its normal high state). It then turns that strobe off, and turns the next one on and re-reads all the returns again. It repeats this until all the strobes are scanned and then starts over. This is how the manufacturers could use up to 8 ins and 8 outs (total of 16 I/O pins) to read up to 64 switches.

So, in normal circumstances, the strobes should all be pulsing and not be either high or low. The state or appearance of the returns are all going to depend on if or how many switches are closed out in the cabinet. The more of the switches that are closed on that return line, the more "Low" your Logic probe is going to show. But it should be either always high, or plusing, never stuck low. This is, however not true of the Outhole or slam switch input as they are special switch inputs wired directly to a ground source.

Remember, is some designs, the dipswitches are also placed on the switch matrix or at least read upon power up via their own select strobes or returns while sharing some lines of the switch matrix. This is NOT, however the case on a N-iwumpf board but is the case for an original Gottlieb System 1 MPU board.

#5 4 years ago

Thanks Cactus Jack, That was a great explanation, I had a feeling that was the way it worked but I really wasn't sure. I need to get back to work on my machine. I got a little burned out with trying to solve this problem.

2 months later
#6 4 years ago

Thought I would just record how this problem was finally solved. I wrote to Ace at Ni Wumpf and he recommended that I ship the board to him. He quickly returned it to me with the explanation that there was some corrosion on one of the solder joints. He resoldered and it is now working well.

Hey there! Got a moment?

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