(Topic ID: 130497)

TerryB's Guide to Logic Probes


By terryb

4 years ago



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  • 119 posts
  • 35 Pinsiders participating
  • Latest reply 46 days ago by mystman12
  • Topic is favorited by 277 Pinsiders
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    There are 119 posts in this topic. You are on page 2 of 3.
    #51 2 years ago

    TTL integrators always use 5 volt supply voltages, do the cmos always use 12v supply voltages?

    Differs by these voltages also if it is CMOS or TTL ?

    #52 2 years ago
    Quoted from pedroborges:

    But in j206 one should not choose TTL since the uln2803 connects in plug j206 ?

    You are correct ULN2803 is TTL and red connector on 12V.

    #53 2 years ago
    Quoted from pedroborges:

    TTL integrators always use 5 volt supply voltages, do the cmos always use 12v supply voltages?

    CMOS chips can use a supply voltage from 5V to 18V.

    4 months later
    #54 2 years ago

    thanks,
    The plug j206 and j207 is tested with the ttl logic probe connected at 12v right?

    The plug j208 and j209 is tested with the cmos logic probe connected at 12v right?

    #55 2 years ago
    Quoted from pedroborges:

    The plug j206 and j207 is tested with the ttl logic probe connected at 12v right?
    The plug j208 and j209 is tested with the cmos logic probe connected at 12v right?

    Correct.

    3 months later
    #56 1 year ago

    thanks ,

    how do I test with the logic probe for the j205 plug and the j212 plug ?

    2 weeks later
    #57 1 year ago

    Great read-through!! Question - Can you use a logic probe to test sound board IC's? Have MC3403 IC that I'm curious about on my Data East sound board. It acts as a amplifier chip. My music part is very faint, almost non-existent but my sound effects are fine...separate IC. Thank you again for your info!

    1 month later
    #58 1 year ago
    Quoted from metalkatt:

    Great read-through!! Question - Can you use a logic probe to test sound board IC's? Have MC3403 IC that I'm curious about on my Data East sound board. It acts as a amplifier chip. My music part is very faint, almost non-existent but my sound effects are fine...separate IC. Thank you again for your info!

    Sorry for the delay in responding, been out of circulation for a while. Yes you can use a logic probe to test IC's on the sound board. If the chip is marginal you won't learn much unless you've worked on enough of them to tell by the tone. Most failures though will definitely be obvious.

    #59 1 year ago

    Busted out my logic probe to work on a Data East Star Trek that has been a headache since purchasing. Was told game worked when we bought it, absolutely no way this game played at all. This was my first time using the logic probe, it was like a whole new world opening up diagnosing transistor failures. This game had 4 parts of the light matrix locked on, sending 15 volts to the controlled lighting bulbs. The logic probe is my new favorite tool.

    The image attached is all of the transistors I had to change out of a so called fully working game. Even let the smoke out of a couple of leds. To start with, someone had the bridge rectifier wired backwards so that there was no power at all to the controlled lighting.

    IMG_3194 (resized).jpg

    #60 1 year ago
    Quoted from Kawydud:

    This was my first time using the logic probe, it was like a whole new world opening up diagnosing transistor failures.

    Glad to hear it. It really is a valuable tool to have in your arsenal.

    4 weeks later
    #61 1 year ago

    OK, here's a question.

    Lets say I am testing a board, and that board has multiple voltages on it. +5, +12, -12, and maybe 36V or something like that.

    What happens if I accidentally probe the 36V line? Will I have a giant ball of lightning and lava in my hand? Will it just pick it up as a high signal?

    In other words, what is the safe high limit for voltage when using a probe?

    #62 1 year ago

    I don't think 36v would smoke a probe rated for 15v max immediately, make it explode, or melt it.
    If I did that I would at least test it by comparing readings to a known good probe before trusting it again. Obviously the higher the overvoltage the greater the opportunity for damage.

    #63 1 year ago
    Quoted from YeOldPinPlayer:

    I don't think 36v would smoke a probe rated for 15v max immediately, make it explode, or melt it.
    If I did that I would at least test it by comparing readings to a known good probe before trusting it again. Obviously the higher the overvoltage the greater the opportunity for damage.

    Well said. Since you're typically working on the logic part of the circuit you really shouldn't have an issue with hitting a high voltage.

    #64 1 year ago

    in this video as you can see was to get the 5 volts to the capacitor.

    I have one doubt that the following: I should not have gone to get the 12 volts ?

    #65 1 year ago

    how do I test the inputs and outputs of the lm339 with the logic probe ?

    #66 1 year ago

    One of the possibilities is to put a jumper from one of the (working) column drives and put it to a row-input you want test. (blue line)
    Yellow marked are pulsing from 12 to zero volts, Red between 5 and zero volts.
    test lm339.jpg

    #67 1 year ago

    to test the inputs - I have to power the logic probe at 5 volts and by the logic probe in CMOS and test the inputs -.

    to test the inputs + I have to feed the logic probe to 12 and by the logic probe in CMOS and test the inputs +

    would be so to test the inputs ?

    is that in this video he tests the columns and row with the probe fed at 5 volts, I think the probe should be fed at 12 volts

    #68 1 year ago

    Great info here. Thanks.

    #69 1 year ago

    On the LM339 you would test the inputs with your probe connected to 12V and the outputs with it connected to 5V. In zaza's drawing the yellow are 12V and the red 5V.

    More info here:

    https://pinside.com/pinball/forum/topic/terrybs-guide-to-logic-probes#post-2514887

    #70 1 year ago

    thanks, in the video test with the feeding probe at 5 volts;
    the probe must be connected to the supply voltage of the integrated ?
    but the test of the inputs to must not be done so for the lm339 ?
    to test the inputs - I have to power the logic probe at 5 volts and by the logic probe in CMOS and test the inputs -.
    to test the inputs + I have to feed the logic probe to 12 and by the logic probe in CMOS and test the inputs +

    #71 1 year ago
    Quoted from pedroborges:

    the probe must be connected to the supply voltage of the integrated ?

    The probe should be connected to the voltage range that you are reading rather than the chip's supply voltage. So if you're taking a reading with a high of 12V connect the probe to 12V and for a high reading of 5V connect the probe to 5V. This is how the probe determines the logic thresholds for a hi and lo.

    I'm not sure what input + and input - mean. To me the inputs are the 12V side and the outputs the 5V side.

    #72 1 year ago

    the input - this is connected to 5 volts in the diagram

    #73 1 year ago

    I can test the inputs and outputs of the all integrated ones with the logic probe powered at 5 volts ?

    #74 1 year ago
    Quoted from pedroborges:

    I can test the inputs and outputs of the all integrated ones with the logic probe powered at 5 volts ?

    No. In zaza's drawing above you should connect the logic probe to 12v for the yellow and 5v for the red.

    #75 1 year ago

    But if you look at the input - the lm339 is connected to 5 volts.
    The two gates of the logic probe have to be connected to the supply voltage as you can see in the link image (https://s13.postimg.org/4kuo23vjr/integrado1.png) or not?

    #76 1 year ago

    The LM339 has 12v inputs and 5v outputs and you have to match the probe to that not the Vcc for the chip (5v).

    #77 1 year ago

    thanks, because, but in the scheme the input- of lm339 is connected to the 5 volts

    for example: I do not know what the voltage is in the inputs of the uln2803, how do I know which is the voltage applied to the inputs of the uln2803 ?

    wpc_95 (resized).png

    #78 1 year ago

    Another example:

    in the power driver board you have the uln2803 that controls the bulbs of the game.

    for inputs and outputs how would you test with the logic probe?

    #79 1 year ago

    switchmatrix (resized).png

    #80 1 year ago

    thanks, in the scheme where it made the markings to an input which is connected to VCC, and vcc is 5 volts.
    the inputs and outputs of the lm339 in what state should they be while testing with the logic probe?
    the inputs and outputs of the uln2803 in what state should they be while testing with the logic probe?

    to -input should not be connected to 5 volts to test with the logic probe?
    the inputs of the 74hc237 is also 5 volt ?

    I have another question to make the forehead with the logic probe on the uln2803 that is on the power drive board.

    in the image I made the mark of the input and output in which I want to know what the voltage is.
    I think the output to the schematic is +18 volt, but I do not know what the input voltage is

    wpc1 (resized).png

    #81 1 year ago
    Quoted from pedroborges:

    the inputs and outputs of the lm339 in what state should they be while testing with the logic probe?

    That varies depending on the state of the switch. See this post.

    https://pinside.com/pinball/forum/topic/terrybs-guide-to-logic-probes#post-2514887

    Quoted from pedroborges:

    the inputs and outputs of the uln2803 in what state should they be while testing with the logic probe?

    The output will be high with low pulses and the input low with high pulses.

    Quoted from pedroborges:

    I think the output to the schematic is +18 volt, but I do not know what the input voltage is

    The input is 5v.

    Posts 11 and 12 in this thread walk you through testing the row and column, including what voltage to connect the logic probe to.

    #82 1 year ago

    the integrated 74hc237 is a CMOS chip right?

    to test the inputs of the integrated 74hc237n I put the logic probe in CMOS and feed the logic probe to + 5V

    to test the outputs of the integrated 74hc237n I put the logic probe in CMOS and feed at +5 volt

    Was this how I should test the logic probe?

    #83 1 year ago
    Quoted from pedroborges:

    the integrated 74hc237 is a CMOS chip right?

    to test the inputs of the integrated 74hc237n I put the logic probe in CMOS and feed the logic probe to + 5V

    to test the outputs of the integrated 74hc237n I put the logic probe in CMOS and feed at +5 volt

    Was this how I should test the logic probe?

    That is correct.

    #84 1 year ago

    Thanks, The 74hc237n connects to the inputs of the uln2803.
    to test the inputs of the uln2803 I put the logic probe into ttl and feed the logic probe to 5 volts.
    To test the outputs of the uln2803 I put the logic probe in ttl and feed the logic probe 12 volts.

    Was this how you had to test with the logic probe?

    Do you know what it is that has to give in the logic probe for the inputs and outputs of the lm339 and for the inputs and outputs of the 74hc237n ?

    #85 1 year ago
    Quoted from pedroborges:

    Thanks, The 74hc237n connects to the inputs of the uln2803.
    to test the inputs of the uln2803 I put the logic probe into ttl and feed the logic probe to 5 volts.
    To test the outputs of the uln2803 I put the logic probe in ttl and feed the logic probe 12 volts.

    Was this how you had to test with the logic probe?

    Correct.

    Quoted from pedroborges:

    Do you know what it is that has to give in the logic probe for the inputs and outputs of the lm339 and for the inputs and outputs of the 74hc237n ?

    Not sure what you're asking.

    #86 1 year ago

    thanks, I want to know what is the result that should give in the logic probe in the inputs and outputs of the integrated to know if the chip is good or not

    for example: the result that must give the input is low with pulses, and the logic probe lights the yellow light and the green light.

    #87 1 year ago

    I bought the eistar lp-1 logic probe and it does not seem like a big deal.
    I was searching and I found the logic probe elenco lp 900, the logic probe elenco 560 and the logic probe Bk precision dp52
    Which of these three would you advise me to buy ?

    #88 1 year ago

    Great thread! Thanks!!!

    #89 1 year ago

    I prefer the Elenco LP-560, which is the one I cover in this guide. It has audio which the 900 does not. The 900 also does not have a cmos/ttl setting. While this might seem like an advantage, in that you avoid the hassle of figuring out which setting to use, the probe uses a hybrid threshold for cmos and ttl and therefore will not always be 100% accurate. It does have a pulser though, but honestly I seldom use the pulser and if I do need a pulse I can always pull it off the board somewhere. I'm not familiar with the BK product.

    #90 1 year ago

    thanks , Could the logic probe elenco lp-560 be connected to +18 volts?

    I saw this logic probe on amazon.com.

    but since I am from portugal, may I have to pay customs fees ?

    #91 1 year ago
    Quoted from pedroborges:

    thanks , Could the logic probe elenco lp-560 be connected to +18 volts?

    Yes.

    Quoted from pedroborges:

    I saw this logic probe on amazon.com.

    but since I am from portugal, may I have to pay customs fees ?

    No idea.

    #92 1 year ago

    OK , thank you

    #93 1 year ago

    I have one of how to test with the logic probe the circuit of the bulbs as you can see in the image.

    on uln2803 I think that in order to test the inputs I had to connect the logic probe at 5 volts and then the logic probe in ttl, to test the outputs of the logic probe at 18 volts and put the logic probe into ttl.

    I think that in order to test the output of the lm339, I turn on the logic probe at +5 volts, and I put the logic probe in cmos.

    to test the entries of lm339 is that i do not know

    lamp matrix (resized).PNG

    #94 1 year ago
    Quoted from pedroborges:

    on uln2803 I think that in order to test the inputs I had to connect the logic probe at 5 volts and then the logic probe in ttl, to test the outputs of the logic probe at 18 volts and put the logic probe into ttl.

    Technically the output should be set to CMOS, although either would work. The rest is correct.

    Quoted from pedroborges:

    I think that in order to test the output of the lm339, I turn on the logic probe at +5 volts, and I put the logic probe in cmos.

    Correct. The outputs are both TTL and CMOS compatible so you could actually use either one.

    Quoted from pedroborges:

    to test the entries of lm339 is that i do not know

    Haven't worked on a lamp matrix in a while, I think 18V and CMOS. If you get weird readings then try 5V and CMOS.

    #95 1 year ago

    thanks, but for the outputs of the uln2803 should not choose ttl ?

    #96 1 year ago

    ULN2803 is a CMOS chip. The inputs are TTL compatible but the datasheet does not say the outputs are TTL compatible so I would go with CMOS.

    http://www.ti.com/lit/ds/symlink/uln2803a.pdf

    #97 1 year ago

    Terry, I recently bought a logic probe and was testing the U14 chip on the WPC MPU board. I was hooked up to 5 volts and was testing the bottom legs of the chip. I was able to confirm the chip was bad, but seconds later i think i shorted between 2 legs of the ic chip. this caused the game to reset. Since the chip was already bad, I couldn't tell if this made things worse.

    I was able to replace the chip with a socket and a new chip, and all is fine now with my game (BSD), but doing that really intimidated me. I came to learn that these tiny legs on ic chips are hard to test in the back box. I have a pretty steady hand, but those suckers have got to be about a millimeter apart.

    My question - is that really bad to short the probe between 2 legs? Will it cause damage? Or is 5 v too little to fry anything.

    For the future, I am going to try to set up a bench tester with computer power supply.

    #98 1 year ago

    but if cpu board tested the outputs of the uln2803 in ttl, the power drive board should not be equal to the test ?

    #99 1 year ago
    Quoted from Elicash:

    ... testing the U14 chip on the WPC MPU board. I was hooked up to 5 volts... ...i shorted between 2 legs of the ic chip. this caused the game to reset.
    My question - is that really bad to short the probe between 2 legs? Will it cause damage? Or is 5 v too little to fry anything?

    When your probe is connected to 5v that doesn't mean the tip is applying 5v to everything you touch. In your example you shorted leg X to leg Y. Looking at the data sheet for a 74LS374 the input voltage is -1.5v @45 ma. Not enough to damage anything even in worst case scenario.

    #100 1 year ago

    If you momentarily shorted 5v to ground you could cause a reset, but it is unlikely you did more damage. There are other CMOS chips though where it's possible to short 12v or 18v to the logic circuit and that will likely blow something.

    My hands aren't as steady as they used to be so I typically use a DIP clip and micrograbber. Normally you're just testing a couple of points so you can set everything up with the power off and then just get your readings from the other end of the micrograbber.

    https://pinside.com/pinball/forum/topic/terrybs-guide-to-logic-probes#post-2517164

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