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My NE555 chips gone bad

Fluffyboii

Member
https://www.reddit.com/r/synthdiy/comments/v2srqh
I made a sequencer for my future synth project and designed a circuit around baby10 design: https://hackaday.com/2016/01/14/oh-baby-baby10-build-a-classic-analog-music-sequencer/

I first wanted to test the oscillator part which is astable 555 and it is the most basic thing in existence but it refused to work properly. I gave up and decided to change the 555 I used and that kinda destroyed some traces but I carefully re-made those connections and tested it again. Which resulted the LED staying on but going a bit lower brightness state for a very small amount of time. Which was related to the resistance between pin 7 and VCC as it should be but still it wasn't the expected 555 behaviour where the LED turns on and turns off continuously with the same turn off and turn on time period. So I gave up on it, thinking it was a connection problem that I kept missing because I was tired.

Today I tested the same thing on breadboard and saw the same exact staying on and going a bit dark behavior which made me go insane. I tried all of the remaining 555 chips and one of them functioned fine and others had the same issue. Interesting thing is there were 3 Texas Texas Instruments NE555s and 2 of them had that problem and I also had another brand's 555 which had the same issue. One of the Texas ones worked fine which was identical with the others and probably bought at the same time which is interesting since broken ones aren't the same brand.

So the final question is, does NE555 chips go bad for no reason like this in the same exact way. The ones I have are at least 6-8 years old and they stayed in my electronic box for years until I needed one of them yesterday. I use to build flip flops with these with no issues in the past and it's simple circuit design is almost engraved in my mind.

Edit: the supply voltage is 12V which is below 16V max stated in the datasheet.
 
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crutschow

Well-Known Member
Most Helpful Member
No, it's not normal for 555 chips to go bad, especially in the same way.
I expect something is stressing them.

Post the schematic of the exact circuit you are using.
 

Fluffyboii

Member
No, it's not normal for 555 chips to go bad, especially in the same way.
I expect something is stressing them.

Post the schematic of the exact circuit you are using.
1654123419847.png


Essentially same thing in this video:
It is not like they are slowly going bad, except one, all of them act like this under same circumstances. Only same thing with my PCB and breadboard is the NE555 and my linear converter +/-12V power supply I build for my synth project. I can also provide the schematic of that power supply but I used another circuits with it and one of them was a sequencer that used 555 as oscillator like this one and it worked fine.
 
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crutschow

Well-Known Member
Most Helpful Member
One design problem I see:
If the 470k pot is turned to too low a value, it could cause excess current to go through DIS pin 7 and possibly zap the 555.
The pot should have a minimum of a 2kΩ resistor in series with it.
 

Fluffyboii

Member
One design problem I see:
If the 470k pot is turned to too low a value, it could cause excess current to go through DIS pin 7 and possibly zap the 555.
The pot should have a minimum of a 2kΩ resistor in series with it.
That explains why they shut down when that happens. But when I was trouble shooting my PCB after changing the NE555 I changed the pot with a 330K resistor just to be sure. In the breadboard I also used a fixed resistor. So that should not be the issue. Should I just get some fresh 555s and see what happens. Problem seems to be special to my old stock even though it shouldn't.
 

crutschow

Well-Known Member
Most Helpful Member
So that should not be the issue. Should I just get some fresh 555s and see what happens. Problem seems to be special to my old stock even though it shouldn't.
If you are sure it's wired correctly than perhaps you need some fresh ones.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Are the bipolar or CMOS ones - eg. LM/NE555 vs LMC555 / ICM7555 / TS555 ??

It's possible some CMOS types are sensitive to handling or static during wiring; there are many variations. They can be sensitive to "latchup" effects if the timing cap voltage is higher than the supply as power is switched off.

They typically also have lower output drive capability.
 

Fluffyboii

Member
Are the bipolar or CMOS ones - eg. LM/NE555 vs LMC555 / ICM7555 / TS555 ??

It's possible some CMOS types are sensitive to handling or static during wiring; there are many variations. They can be sensitive to "latchup" effects if the timing cap voltage is higher than the supply as power is switched off.

They typically also have lower output drive capability.
All of them are NE555s not the CMOS one.
 

Fluffyboii

Member
I just used the good one in the bunch. I would normally get some fresh stock and don't put my trust on that single working one but I needed it going fast and it works fine for now. At least if it fails I will know.
 

Dick Cappels

Active Member

For The Popcorn

Active Member
One suggestion – if you aren't sure the circuit is correct and you fry a chip, maybe try ONE more and see if the same thing happens. Don't keep trying chips if the circuit may be burning them up.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
One suggestion – if you aren't sure the circuit is correct and you fry a chip, maybe try ONE more and see if the same thing happens. Don't keep trying chips if the circuit may be burning them up.

When I was at college, we were spilt in to two teams and both given the same project to do - the project had been 'knocking round' for a number of years, and we were the first year they thought worth trying it with.

Essentially it was a crude one armed bandit, just using three 7 segment filament displays spinning the three horizontal segments, and you had three buttons, and had to stop the three bars in a line to win by pressing the buttons. (I can't help thinking you could do this now in 20 minutes with a PIC :D )

All we were given was a block diagram, which showed ring of three counters, bistables, astables, logic gates etc.

We were only allowed to use discrete components (but IC's were fairly rare back then anyway), and it had to be built in separate modules on plain matrix board, with all components and wiring on the top, as it was going to be used in an open-day exhibition.

Each team was split into smaller teams, and allocated a specific part of the design - and off we all went to the college library, no Internet (or home computers) back then.

I was basically head of one team, and another guy (who's name I've long since forgotten) was the captain of the other team. We were well ahead (I seem to recall I built the ring of three counters?), as the other team were struggling - and eventually they decided to merge the two teams.

The reason for this ramble, and the reason for the lack of progress of the other team, was down to their captain who was building the three astables - he was powering them from 9V, and the transistors were blowing due to reverse Vbe failure (as you would expect). I pointed out to him that the failure was expected, and he could cure it by adding protection diodes, or by lowering the supply rail.

Anyway, he wouldn't listen - and continued fitting transistors, blowing them, and replacing them again - to the extent he had a LARGE pile of dead transistors on his desk. Eventually, by random luck, he managed to find six transistors which were over spec. enough to survive a 9V supply, so did manage to cmplete the three astables.

So, as 'For The Popcorn' said, don't keep repeatedly blowing devices - hoping to find ones that might be over spec. enough to work, find what's wrong and fix it.

The guy from college went on to be a teacher of the course - as they say, those who can do, those who can't teach :D
 

For The Popcorn

Active Member
Where I used to work, we were split off from another group. As part of that split, we got one SD335 spectrum analyzer, leaving them with four.

One day, their technician asked if they could borrow a card from our spectrum analyzer to test out a problem in one of theirs. Since I knew they had four, and no remote trials were in progress, I asked him was was going on. One of their analyzers had a problem with this card, so they swapped it with a card from another analyzer. Now that one didn't work either. Pretty soon, there were four analyzers spread across the bench. And four dead cards!

"NO, I'm not giving you our cars to destroy too! What the heck are you doing?!?"
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Where I used to work, we were split off from another group. As part of that split, we got one SD335 spectrum analyzer, leaving them with four.

One day, their technician asked if they could borrow a card from our spectrum analyzer to test out a problem in one of theirs. Since I knew they had four, and no remote trials were in progress, I asked him was was going on. One of their analyzers had a problem with this card, so they swapped it with a card from another analyzer. Now that one didn't work either. Pretty soon, there were four analyzers spread across the bench. And four dead cards!

"NO, I'm not giving you our cars to destroy too! What the heck are you doing?!?"

They obviously had no idea how to repair things :D

One extra dead card would have been enough - when swapping the card didn't work, you next try the original dead card in the second machine, which obviously wouldn't work. You then try the second dead card back in it's original machine, which again doesn't work - so you now know the first machine has a fault that's killing both cards.

Trying any more cards is just stupidity :D
 

For The Popcorn

Active Member
They obviously had no idea how to repair things :D

Trying any more cards is just stupidity :D

This guy was reasonably competent, just having a bad day I guess.

But believe me. I'm sure I used the word "stupid" after I told him no, probably with several adjectives in front of it!
 

Fluffyboii

Member
Ok I got 3 new 555 chips. 2 from another store 1 from another. They all act the same. Timing is wrong af. One led of flip flop lights up for a milisecond and the other led turn off for a milisecond.
 

Fluffyboii

Member
Ok there is something wrong with that circuit that causes the timing problem. Another circuit with high value resistor between 6 and 7 instead of 7 and positive works nicely.

Edit: Apperently that circuit really ment to put a %99 duty cicle. So the whole thing was actually properly working.
 
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