You need to ensure you are using the appropriate setting (TTL/CMOS) and that the 5v AND gnd clips are connected to the proper reference sources. It should give you a constant pulsing when the output is floating or infinite resistance.

The column signal is pulsed so it sounds like you are getting the correct reading. When in doubt just compare the reading to another working reading--in this case another column.

Every logic probe works slightly different. All the columns, when active, should read the same, so if the one reads different that's likely your problem.

U52 is an AND gate. If pin 9 and 10 are high then 8 should be high. Pin 9 will be a pulsed signal, so when it pulses high, pin 8 should pulse high (of course presuming that 10 is high). You can compare this to strobe 7, which would be pins 11, 12 and 13. Do all of the testing while in all lamp test.

Your probe really doesn't seem to work the way mine (and I have several) would in this situation. What make and model is the logic probe and can you post the manual (or point to it on the web).

Are you sure that pin 11 is not reading narrow high pulse (the green led blinking very rapidly). That would be the expected output based on the two inputs.

Other than the blanking signal, which will always be high, the other input and the output are going to be pulsed signals. While the lamps look like they are "on" they are actually pulsed at 500pps. So other than blanking you should not read a high as the other input or the output.

In any case it sounds like the IC is not functioning properly.

No problem, always happy to help someone who wants to learn as they fix their machine.

Basically the blanking circuit is there to prevent solenoids, flashlamps, controlled lamps, etc. from coming on if the CPU doesn't boot up properly. So when you first turn on the game the blanking circuit is low and after the CPU boots up (2-3 seconds), the blanking circuit goes high. This then enables the flashlamps, etc.

So in your case pins 8, 9 and 10 read as I would expect a working circuit to read. The blanking circuit (pin 10) is high, pin 9 is high+low and the output on pin 8 will exactly match the input on pin 9 (high+low).

On the other hand the other circuits don't appear to be correct--high+low input and a narrow high pulsed output. Again the input and output should match since the blanking circuit is always high.

Although I don't have a lot of system 11 experience, I do know how an AND chip works. I'm not sure why you're getting the readings you are: the circuits that work give bad readings and the one that doesn't work gives what I would consider a good reading. Without having the board in front of me I'm at a loss at this point to explain what you're seeing.

The only reason I point at the IC is because the circuit that doesn't work reads differently than all the working circuits. Honestly at this point I would throw a scope on the circuit, but I presume that's not an option.

FYI - The mem/pulse switch should be on pulse and the ttl/cmos switch should be on ttl when testing 5 volt circuits and the switch on cmos when testing 12 volt circuits (in this case you would also connect the red lead to a 12 volt source).

If you compare strobe 7 and strobe 8 at the connector (this would be using the cmos setting) what do you see?

Here's the 7408 datasheet, click on the download link and the PDF will include a truth table for the AND gate which may help explain how it works.

http://www.electroschematics.com/8891/7408-datasheet/

I've asked barakandl to jump in and see if there's something I'm missing.

Just had another thought. With your DMM check the voltages on all of U52's pins (DC setting).

I would check the voltage on all of the U52 pins first. We could have a low voltage giving some flaky readings on the logic probe. That's really the point of going to an oscilloscope so that you can see both voltage and pulses.

Checking the voltages with a DMM should provide the same info.

As an aside, the Mem/Pulse switch on your probe represents "memory" and pulse. In Mem mode, a single pulse will cause the pulse LED to light and stay on. In Pulse mode, the pulse LED should flash for every logic transition leading edge.

As an example of use, if you wanted to know whether a switch activates intermittently while playing a game, you might use the "Mem" mode. If you're looking for a steady strobe or a clock, you would use the "Pulse" mode.

Thanks rancegt. I knew I couldn't type a post that long without messing something up.

That makes me worry a little about your probe. In "Mem" mode, the pulse light should lock on almost every time you touch a circuit, regardless of the voltage.

Let's straighten out your logic here:

In
9 - 0,54
10 - 4,50
Out
8 - 0,71 Vdc

In
12 - 0,54
13 - 4,50
Out
11 - 0,32 Vdc

In
1 - 0,54 Vdc
2 - 4,50
Out
3 - 0,32

These are all AND gates, which means input one high AND input two high will create a high out. All other conditions will read low. All of these gates are reading as I would expect.

It seems as if the edge detection circuit in your logic probe is not working. I would suggest either have someone with more experience check it and see what they think, or replace it.

As for your problem, you may want to start a new thread with a "System 11 Lamp Matrix" title, and work through the problem that way.

That's a good starting point. The experienced System 11 guys will jump in and walk you through the steps for troubleshooting. In this thread you have a couple of guys who are comfortable with logic probes, but neither of us have a lot of System 11 experience.

I agree on all points. Sounds like a flaky logic probe and a new post to get the system 11 guys involved would be great. Please provide a link here for rancegt and myself to follow along.

I would just describe the problem and go from there. Since the info from the logic probe is suspect I would ignore all readings you've gotten from it or the issue will just get confused again.

Best not to test the lamp matrix with the machine in attract mode, especially when trying to compare the signal on one pin to another. The lamp matrix and associated logic gate circuitry is driving the lamp matrix according to the lamps that should be lit at that instant. Sometimes in attract mode, the entire lamp matrix goes dark and it is possible that an entire row or column is on or off which will appear to give you inconsistent readings. Better to test in "all lamp test" mode.

The simple way to verify if U52, U53 or any AND gate that is used to enable/disable based on the blanking signal is to: 1) verify the blanking input to the gate is high; 2) compare the other gate input signal to the gate output signal.

If your logic probe looks the same when probing the inputs and outputs, you can fairly safely move on and assume the gate is good.

If the signal is not the same, measure it again. If it is still not the same, check the circuitry (transistor in this case) after the gate to see if it pulled down (or up) the output and is effecting the gate's output or blown the gate's output. Use the diode test to check the transistor, in this case.

Measuring the voltage with a DMM on the inputs and outputs of the gates in the lamp matrix is not valid since these are pulsed signals. The duty cycle at the instant you measured the voltage will influence the measurement. You need to use a logic probe or o-scope.

Back to the original problem, what exactly are you trying to fix? Can we have a detailed description of the problem on your Jokerz? Is it one lamp not working or a whole row or column of lamps? Have you checked all the diodes in the row or column?