68kMLA Classic Interface

This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.

Click here to select a new forum.
Cap explosion on SE/30–help!
Posted by: mloret on 2023-03-12 09:20:47
Hello! A friend and I just finished a recap of an SE/30. We did the analog board, logic board and PSU. Finally went to test and cap at C7 of logic board burned up and exploded. Not sure what I did wrong. I have pictures that verify that I oriented it in the right direction. There was a lot of corrosion on the pads and one of them looks to be on its last leg. Any idea what could have gone wrong here? Not sure what the next step should be.
Posted by: Bolle on 2023-03-12 09:29:48
I have pictures that verify that I oriented it in the right direction.
Except that it's not. On Tantalums the stripe marks the positive terminal.
Looks like the others are the wrong way around as well.
Posted by: mloret on 2023-03-12 09:50:55
Omg. I feel like an idiot. Thank you.
Posted by: Phipli on 2023-03-12 10:09:26
Omg. I feel like an idiot. Thank you.
Don't beat yourself up about it, why on earth do one type of caps have marks on -ve, and another on +ve. They're the idiots not you.

But you should perhaps double check polarity of parts in the future 🤣
Posted by: Skate323k137 on 2023-03-12 10:40:48
Don't beat yourself up about it, why on earth do one type of caps have marks on -ve, and another on +ve. They're the idiots not you.

But you should perhaps double check polarity of parts in the future 🤣
I agree it's pretty tough as a standard that they're reversed. I like that Console5s business cards literally have this warning on them though.

I love component testers, even a cheap one to rule out clearly faulty or out of spec caps before installing them pays dividends.
Posted by: mloret on 2023-03-12 13:05:22
Thanks for the advice. Is it possible to use the multimeter to determine polarity of a cap? I'm thinking put it on high Ohms, connect black prob to negative, red prob to posiive and see if I get a reading...is this correct?
Posted by: joshc on 2023-03-12 13:20:18
1678652404409.png
Posted by: Skate323k137 on 2023-03-12 14:03:45
Thanks for the advice. Is it possible to use the multimeter to determine polarity of a cap? I'm thinking put it on high Ohms, connect black prob to negative, red prob to posiive and see if I get a reading...is this correct?
Multimeters aren't really meant for testing capacitors. Get something like this;

Transistor Meter, Aideepen LCR-TC1 Multi-Function Capacitance Resistance ESR Tester 1.8" Full Color Display Transistor Meter for Diode Triode Capacitor Resistor Transistor LCR ESR NPN PNP MOSFET https://a.co/d/6NHTVpv

You'll never have to calculate resistor bands again ever, either.
Posted by: smrieck511 on 2023-03-12 14:17:32
Hate that this happened to you and hope you get the board working soon. An understandable mistake considering the way regular electrolytics are marked.

but, you did me a big favor by scaring the .... out of me as I'm about to recap with tantalums (polymer) this week. I will be extra certain about the polarity.
Posted by: Byrd on 2023-03-12 14:59:37
View attachment 53562

Every single time I recap a Mac I google this very image. Could I print it? Apparently not 😃
Posted by: Phipli on 2023-03-12 15:00:44
Every single time I recap a Mac I google this very image. Could I print it? Apparently not 😃
Tattoo time?

Next to your resistor codes and speeds and feeds tattoos?
Posted by: 3lectr1cPPC on 2023-03-12 16:53:55
Don't beat yourself up about it, why on earth do one type of caps have marks on -ve, and another on +ve. They're the idiots not you.

But you should perhaps double check polarity of parts in the future 🤣
Even worse are pentium 4 and similar era motherboards. They all have stripes silk-screened onto the board under each electrolytic capacitor. Only that some mark the positive and others mark the negative. Keep in mind that these are all for electrolytic capacitors which always stripe the negative side.
Posted by: Byrd on 2023-03-12 20:10:57
Tattoo time?

I've heard of worse tattoos! Maybe my entire back could be that of the periodic table 😀
Posted by: Skate323k137 on 2023-03-12 21:22:51
Tattoo time?

Next to your resistor codes and speeds and feeds tattoos?
I've considered getting the symbol for electrical ground/earth on my leg. When I had lung surgery (many years ago) I woke up after the procedure to find a patch of my leg shaved above my ankle. I curiously asked about it and apparently that's where I was grounded for the electrocautery. Sadly, I could not get the surgeon to provide any further schematics or recommended operating voltages for myself lol 😆 😅
Posted by: Scott Baret on 2023-03-12 22:03:00
I've heard of worse tattoos! Maybe my entire back could be that of the periodic table 😀
I once had a student joke about getting the quadratic formula tattooed on the wrist to avoid memorizing it. (No, it didn't happen, thankfully...my students have all memorized it through practice!)
1