SMD capacitor polarity indicators

[Randall]

I don't do much SMD, but occasionally I will. My Weller soldering station stopped getting hot. I tried a new soldering pencil, but it made no difference. Then I found a pretty easy possible fix, replacing a 2.2uf cap that is known to fail.

My question is how the original caps are marked. They are small aluminum can caps with a black stripe down about 1/3 third of the top surface. I have read in several tutorials that the stripe marks the negative side, and maybe just as many saying it points to the positive side.

Can you gents say with authority which side the black stripe is pointing to?

[nosaj]

Black stripe or half the cap marked black has been negative for me.
nosaj

[Chuck H]

I just looked up images in a *oogle search and,.. It's kind of hard to explain. Any full stripe that isn't black indicates + whereas any black bar (incomplete stripe), dip or black end indicates -. I recommend doing the same search for yourself to be clear on it because it looks like standards in SMT electrolytics were variable for a while. Not knowing the age of your Weller you need to know what older markings look like to identify how it's installed and newer markings to know how to install the new one.

[Jazz P Bass]

Round can capacitors: Black Stripe is negative.

[g1]

Round can capacitors: Black Stripe is negative.

Unfortunately., those black rectangular ones look too much like diodes (where the band indicates cathode).

[Randall]

Mine look like the first two on the left in the photo above. Weller was purchased new about 10 - 11 years ago for what that's worth. WES51

[nevetslab]

Weller was purchased new about 10 - 11 years ago for what that's worth. WES51

Oh horrors. I hate it when a highly reliable/respectable company gets bought out! I wasn't aware of that....thanks for the warning/mention.

[Jazz P Bass]

Which capacitor is at fault?

[The Dude]

Yes. The black stripe is neg. Also, note the base shape- square on one side and angled corners on the other. Lots of times, there is a corresponding shape printed on the board.

Edit: Here's a pic showing the PCB markings I'm talking about.

[Randall]

I am sorry, but I did not mean Weller the company had been sold, I have no idea about that. I meant MY Weller was purchased by me for my bench about 10 - 11 years ago.

"Which capacitor ia it?"

There are only two small round metal caps on my board, 2.2uF and 33 uF.. Some pages Ive read call the 2.2uF into question, and since it's easy enough to swap it out, that's what got me here. There is no nomenclature to work with, no shapes printed on the board, so all I can tell you is it's the 2.2uF I'm focusing on. And now, unless someone says otherwise, I'm going with black stripe is negative.

[Randall]

Doesn't matter much now, I pulled the original cap and it reads 2.2uF, so I guess I was barking up the wrong tree there.

[Chuck H]

Doesn't matter much now, I pulled the original cap and it reads 2.2uF, so I guess I was barking up the wrong tree there.

Maybe not. It's commonly expressed here that "in circuit" conditions for electrolytic capacitors aren't recognized by most testing conditions out of circuit. Since the cap you're replacing has been called out I would go ahead with the plan and see what happens.

[Jazz P Bass]

So, troubleshoot it.
Do you have 5 Vdc.
Is the reed switch closing.
Is the PIC commanding the BC547 On.
Is the triac good.

[Randall]

Can anyone point me in the right direction? I haven't been able to find a schematic.

[The Dude]

Is that not the schematic Jazz gave you in post #8?