74HC74: Testing for damage - Page 1
Forum section: electronics / beginners

author: 13hm13
author_rank: Frequent Contributor
timestamp: February 27, 2023, 11:34:27 am
content: It's possible I damaged a few Philips brand 74HC74 (14-pin, DIP) IC's by reverse biasing them.Not sure what (if any) damage was done. But the accident happened years ago, and I simple put the questionable ICs in bag labeled "Damaged???"They were originally a part of an audiophile CD player re-clock circuit. And the CK was an oscillator. So I suppose I could feed them the same I2S signals and look at the o'scope.And that might look okay or not.If traces LOOK okay, the ICs may still be damaged -- yes?Could damage benuanced--- say, the signal has a TINY bit more jitter or noise than an un-damaged IC?How can one determine the long-term reliability of these ICs?

author: langwadt
author_rank: Super Contributor
timestamp: February 27, 2023, 11:46:08 am
content: if you even suspect they are damaged throw them out, they are dirt cheap

author: Zenith
author_rank: Frequent Contributor
timestamp: February 27, 2023, 12:53:26 pm
content: Agreed. If you have doubts about them, in view of how little they cost they are hardly worth wasting time on. They certainly shouldn't be used for anything important.I believe manufacturers attempt to estimate long term reliability with tests designed to stress their product with cycling to high temperatures and higher voltages. They have a lot of chips to work with and statisticians to work through the data. Over years they can also compare their tests with real world reliability.

author: Stray Electron
author_rank: Super Contributor
timestamp: February 27, 2023, 03:32:20 pm
content: Quote from: langwadt on February 27, 2023, 11:46:08 amx2. There's an saying among hams, "When in doubt, throw it out".If you really want to try and see what's going on with them, I would start by connecting each pin to a Curve Tracer and characterize it and compare to the curve from a known good part. If all of the connections tested Ok then I would then set up some kind of crude pattern generator and test the inputs and outputs for the correct logic functions.

author: Ian.M
author_rank: Super Contributor
timestamp: February 27, 2023, 06:24:29 pm
content: Also check the quiescent current is in spec. for both states of both flipflops, with all inputs held at a valid logic level.

author: Gyro
author_rank: Super Contributor
timestamp: February 27, 2023, 08:14:50 pm
content: It seems a pretty straightforward decision. You violated the Absolute Maximum Ratings of the devices by reversing the supply, both in supply voltage specification and probably absolute maximum supply current too.If they are intended for inclusion in something that you are shipping or selling to somebody else (ie. a product) then you should certainly throw them out. If they are for playing around on the bench for your personal use as a hobbyist (doesn't sound like the case) then they will probably mostly work but you should be prepared for the wasted time and frustration of one of them failing or not meeting spec.In terms of whether they are damaged in some subtle way, nobody here can tell you. If pressed, the answer must be yes they are - you violated the Absolute Maximum Ratings so all bets are off [EDIT: including long term reliability].

author: james_s
author_rank: Super Contributor
timestamp: February 27, 2023, 08:22:07 pm
content: What are you planning to use them for? If it's for hobby circuits then test them out and if they seem to work and aren't getting hot then use them. If you're going to put them into a customer item or something critical then just don't. Or just toss them to be safe but personally I'd probably use them for non-critical projects.

author: 13hm13
author_rank: Frequent Contributor
timestamp: February 27, 2023, 08:40:19 pm
content: Thx for everyone's feedback!It was HOBBY project. I completed the orig project with the many duplicate parts in my bin. And that made the project work! But I may have made some other error and blamed the 74HC74's incorrectly -- IIRC, it was rush job, and I was impatient to complete the hobby project.Troubleshooting these potentially damaged ICs is intriguing. Maybe they are not damaged.Perhaps some of you can devise a quick-n-clean way of plugging-chugging these ICs --testing for damage.Say a breadboard setup. Or even using something like:

author: wasedadoc
author_rank: Super Contributor
timestamp: February 27, 2023, 08:55:05 pm
content: Quote from: 13hm13 on February 27, 2023, 08:40:19 pmNo, a waste of time. That will not give any useful result. Nor will a curve tracer as suggested above.

author: james_s
author_rank: Super Contributor
timestamp: February 27, 2023, 09:14:36 pm
content: That's not an IC tester, that's for testing discrete components like transistors, diodes and passives. IC testers do exist, although they are pretty much a go/no-go test, they won't find subtle damage.

author: janoc
author_rank: Super Contributor
timestamp: February 27, 2023, 09:27:40 pm
content: Quote from: 13hm13 on February 27, 2023, 08:40:19 pm7474 you can easily test on a breadboard, that's just 2 D-type flip-flops. A power supply, few buttons for inputs and LEDs to indicate output states should be enough to give you an idea whether they work at all or not. The datasheet describes the function pretty well. And you may also learn a bit about basic logic circuits.That transistor tester is useless for it, it can't test logic chips. There are dedicated testers and some universal programmers are able to test logic ICs but that's an expensive overkill here.

author: Zero999
author_rank: Super Contributor
timestamp: February 27, 2023, 09:31:24 pm
content: I agree with the consensus: toss them out. It's just not worth the time an effort debugging.If you must test them, measure the quiescent (when it's not doing anything) current, as mentioned by Ian.M. In addition to that. Test the basic functionality. Read the data sheet.

author: shapirus
author_rank: Super Contributor
timestamp: February 27, 2023, 09:48:08 pm
content: Quote from: james_s on February 27, 2023, 08:22:07 pmthis.Chances are that those ICs will work just fine if they aren't outright burned. Not for anything critical, yes, because chances also are that there is subtle damage. But for non-critical hobby stuff, for playing around and learning, I see no problem. Who cares if they for example fail to meet the datasheet specs at 70°C, but work fine at 50°C, or only fail in edge cases which will never happen in the device they will be a part of? Come on, nobody's life will depend on them. Why throw them out and create unnecessary waste?Mark them accordingly so as not to mix them up with the good ones. Use sockets instead of soldering them directly so that they can be easily replaced if the circuit doesn't work correctly and you suspect it may be the IC.Additionally, if they do fail or show strange behavior, it's for the better: the question of what exactly can go wrong after applying the wrong power polarity will have an answer.

author: shapirus
author_rank: Super Contributor
timestamp: February 27, 2023, 10:01:52 pm
content: But as far as actually testing them to make sure they are not damaged at all, you'd have to basically repeat everything shown in the datasheets in the parameter testing circuit section (and in addition devise a number of your own circuits to test the rest of the parameters), and do that over the entire operating temperature range. Therefore the answer to the original question is: it is not viable at all.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 27, 2023, 10:08:33 pm
content: For each flip-flop, connect notQ to D, then apply pulses to the CLK inputs. At the Q output you should see half the frequency of the CLK pulses (Q should be twice as long if CLK has 50% duty factor).

author: Zero999
author_rank: Super Contributor
timestamp: February 27, 2023, 10:16:03 pm
content: Quote from: shapirus on February 27, 2023, 09:48:08 pmAt the very least, keep them separate or label them. That way, if there's a fault, you can always switch to a known good IC, so you know whether it's your circuit, or the component.

author: 13hm13
author_rank: Frequent Contributor
timestamp: February 28, 2023, 06:05:39 am
content: All four ic's in the "Damaged" bag tested fine.I compared to known good Philips 74hc74 from same order.Set up the re-clock unit per the audio ckt., on a breadboard.MCK (CP1) and BCK (D1) from xmos-based USB adapter (it outputs I2s).The adapter was USB connected to computer for power and signal.The photos with the single pen is known good.Both Q1 and Q1 (bar) are shown.Two pens is straight BCK out from adapter (no 74hc74 ic used)

author: Gyro
author_rank: Super Contributor
timestamp: February 28, 2023, 08:35:31 am
content: If those breadboarded traces are enough for you then fine, you're good to go - Personally, I would have done that before starting the thread.

author: 13hm13
author_rank: Frequent Contributor
timestamp: February 28, 2023, 10:12:50 am
content: Quote from: Gyro on February 28, 2023, 08:35:31 amCleaned up my game a bit further with better decoupling and grounding and playing with PSU voltage. Getting some very clean BCK traces now....Tweaking and iterating ... tweaking and iterating a Philips 74HC74 flip-flop. MCK and BCK entering via same method --- the USB Amanero: