my 555 keeps overheating in my ugly face?

[foxfire]

i started this in another post but, i wanted to be more specific now. i have tried 3 radio shack cmos555's one overheated and only kind of works now, the never worked and the third works but still overheats. i have played it for 15min. or so without any problems and i've played it for 5min. and it overheats. i'm new to ic's so i don't know if this indicates that i've got a mistake in my pedal or just bad ic's?

[oldrocker]

When I first breadboarded this I was trying out different 555 IC's.  I fried a CMOS TLC555 when I stuck in the wrong holes.  By the time I noticed it the chip was toast.  After prefboarding it I kept feeling the chip to see if it was heating up and it never even started to get warm.  So IMHO I would say something is still not totally right.  I would still look at trying a known good chip in there one more time.  Radio Shack sells them fairly cheap.

[ambulancevoice]

if you cant seem to figure it out, just make an ic heat sink but getting a heatsink roughly the same size as the ic and use some heat sink paste or some of that doublesided thermal transfer adhesive stuff and adhere the heatsink to the top of the ic

[foxfire]

i think i'll try getting some 555's from another place just to see if it might be the chips themselves and while i 'm waiting for them to arrive i'll spend another hour or so looking for mistakes and then i'll do the heat sink trick because nothing else will work and because of the nature of the pedal it won't get used all that much so why spend so much time on it?
i typed that whole sentence with just one finger, hooray! thanks again for the tips.

[ambulancevoice]

how have you been handling the ics?

[foxfire]

probably not correctly. as much as possible i tried not to touch them with my fingers. i've been using needle nose pliers with rubber handles, mostly.

[the_random_hero]

probably not correctly. as much as possible i tried not to touch them with my fingers. i've been using needle nose pliers with rubber handles, mostly.

You sure you're getting correct voltages on each of the IC's pins? Try a different brand of IC's, if you're still nuking them then you have a wiring problem.

[dr]

...seems to me I encountered this a while ago-some 555's only work with 5volts, and some work with higher voltages-can't remember which or why.....

[brefmint]

Hey FireFox,
I just built an Ugly Face from that same layout last night. I had a Radio Shack CMOS 555 chip get really hot and after about 10 mins. of sounding great it quit working. I put in a different brand of CMOS 555 ad it started working great again. I played it for another 20 mins. without any issues. I'm just wondering if you ever solved this issue with your UF. I don't want to take mine to gigs if something is screwy with the layout.

Thanks for any help!

brfmnt

[rankot]

Hey FireFox,
I just built an Ugly Face from that same layout last night. I had a Radio Shack CMOS 555 chip get really hot and after about 10 mins. of sounding great it quit working. I put in a different brand of CMOS 555 ad it started working great again. I played it for another 20 mins. without any issues. I'm just wondering if you ever solved this issue with your UF. I don't want to take mine to gigs if something is screwy with the layout.

Thanks for any help!

brfmnt

Could you please take a look and report what kind of 555 you put inside and made it work fine? I have the same problem with TI TLC555 on my board - getting hot after some 10 minutes! 

[blackieNYC]

My TLC555 works fine, and my face is at least as ugly as yours!

[Rob Strand]

I don't understand what the problem is as 555's aren't in the habit of overheating unless the output or pin 7 is carrying a lot of current.   I'm not sure what schematic people are using but that circuit uses pin 4 in a weird way so maybe the difference between the cmos 555 and the bipolar NE555 is the input protection diodes on pin 4.
Connect two 1N914/1N4148 diodes to pin 4 (*without* the resistor) as shown in the schematic below:

http://minimopar.net/perf/images/eepc-basic-input.gif

No guarantees but easy to try.

[rankot]

I found out what is wrong, TLC555 was quite fine, but I have accidentaly used 10k instead of 100k for volume pot.