Belleville, MI
I got the Elenco probe suggested, but testing a couple chips on my Strikes and Spares lamp board, the sound changes when the bulb I'm probing for lights up, but the high/low indicator never does?
(Topic ID: 130497)
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Quoted from PinballAir:I am unfamiliar with whether or not a logic probe has continuity but is it possible by testing the bulbs you are grounding a transitor?
I'm not testing the bulbs, I'm probing a chip on the lamp board - the sound changes when the corresponding light turns on, and changes again when the light turns off, but the high/low state indicator on the probe never changes -
Quoted from Blake:First thing to do is pull up the data sheet for the IC your probing. Confirm if it’s TTL or CMOS. Set prob jumpers to appropriate voltage and ground.
Then from the data sheet identify which legs are supposed to do what. High-low-toggling exc.
Remember the corresponding leg could be held high or low, change state from high to low or low to high, or toggling from high or low.
I would look through your manual to understand how your probe interprets signals.
Once you understand what the probe is doing. Then identify if what you see on the probe matches to what is shown on the data sheet. If not you could have a problem with that chip or possibly some component beforehand.
Its a CMOS chip, and the entire circuit is working fine, it ended up being a cold solder joint - here's the chip below (original is obsolete, that's the replacement) from both the datasheet and the lamp board schematic.
Pins 5 and 6 are both feature lamps, so I was comparing those and the results were identical (like i said, problem wasn't the chip). No manual came with the probe (ELENCO 560), but if the chip output is controlling a lamp, it's obviously changing state, no? As I said, the staticky SOUND changed when the corresponding lights lit up, but the HI/LO indicator on the probe never changed - if i remember correctly it just stayed low -
chip (resized).PNGchip 2 (resized).PNG
Quoted from robertmee:Well, the obvious check is to try and few other circuits...hell, just probe the 5v test point and see if your probe behaves as expected.
Yep, probed the test point, it goes HI.
Probed the legs I was working on earlier, it stays LO then the PULSE light comes on when the sound changes/bulb lights up.
So I guess by looking at this truth table for that chip, all of the outputs are going to be LOW -
Capture (resized).PNGQuoted from Quench:This is the correct indication. See terryb's 5th post in this thread.
In this application, the 4514 pins are mostly low except for a very brief high pulse on outputs enabling a SCR to illuminate its respective lamps.
Ok, thanks Quench (and Terry B)!
I see what Terry said now - "Also remember that IC datasheets are your friend. The datasheet for any IC will typically provide a truth table that will tell you what the output should be based on the possible inputs."
So Quench, as someone who's repair experience is well documented on here, how often do you use a truth table to determine what an output should be? Is it considering "cheating" as opposed to deciphering a circuit to figure it out? Or when it comes to these Bally/Williams games, do you have these various chips memorized by now?
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