HAVASUGAMEMAN
Member
what is the best way to check and see if a chip is bad? I want to check chip 7402 (12a) on the cpu board it is in the spec coil switch input circut .this is in my batman mach.
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
DarrenF;1769896 -Damn the testing... if you have good reason to suspect it said:Exactly. You're talking about a $0.39 part, save yourself the headache and try a new one.
Chris
-There's a semi-ghetto method of using a DMM in diode-check mode to test for bad lines. I don't really know the details of this method, as I usually use my logic probe. Go here, then scroll down to "testing chips" http://www.pinrepair.com/begin/index.htm#howdmm
Randy Fromm covers this in his beginning arcade repair video as well - my question - has anybody actually found this useful? I'd tried it a few times in the past and it really didn't help me isolate which chip was bad, so I'd kinda blown it off. Essentially, you're using your meter in diode testing mode, and looking for similar results (.4 to .6) on the inputs/outputs. I've yet to have this identify a bad chip, although Randy notes in his video that he doesn't even bother using other methods any more as it works so well for him...
I too have gone with the logic probe, and reviewing schematics to help identify likely areas of failure.
-Damn the testing... if you have good reason to suspect it, just replace it.
This is an excellent method, and one that I use frequently. What you NEED though is a good board reference - something to compare your results against, otherwise the numbers don't mean much.
Chris
Exactly. You're talking about a $0.39 part, save yourself the headache and try a new one.
Chris
Sure, if it's socketed, you have a replacement on hand and you really suspect the IC is bad. Something that's not socketed I would definitely be taking 30 seconds with a logic probe to make myself feel better about digging into the board. Testing simple gates with a logic probe takes very little time. It's probably a good idea for a lot of pinball repair people to take a bit of time and actually learn how this logic works and what it does in the context of a pinball circuit board anyway.
Well, I wasn't the first one to suggest this, I was agreeing with Darrenf (the guy who first said it) and, additionally, pldoolittle (another guy who agreed with Darrenf).
Chris
We can all do it different ways and still be right.