Capacitor blew up, what did I do wrong?

[ra-ma]

Hi, in this link I described my new function generator and an issue I do have in regards to peaks:

https://www.eevblog.com/forum/testgear/exact-electronics-model-119-function-generator-looking-for-schematicdocu/msg1478541/#msg1478541

While measuring today with the oscilloscope I found that the spikes are also in the +/- 15 volts internal supply, in the timing absolutely parallel to the spikes in the curve. Therefore I decided to replace the existing capacitors by new ones as the whole machine is some decades old. I couldn't see fluid leakage or measure a short circuit or much too high/low capacitance but whatsoverer changed the caps.

When turning on the function generator after the change, everything looked fine. +/- 15 volts were available and also the spikes seemed to be much less than before. But during my further measurements after a couple of minutes - a big boom - and one of the capacitors blew.

What did I do wrong? Yes, the new capacitors have a higher capacitance, but voltage fits and I'm very sure that polarity was ok too. Any hints? 

[janoc]

Are you really really sure about the polarity? Because this is exactly what happens when you solder in the electrolytic cap the wrong way around, especially when it happened shortly after powering the device up.

[cvanc]

Agreed; what happened is the classic reversed polarity failure mode.

[ra-ma]

OK, thanks. I'll try it tomorrow again and check also the other capacitors for correct polarity.

[james_s]

One thing to watch out for is that silkscreen errors are not terribly uncommon. I have worked on several devices where the printing showed the wrong polarity. If in doubt follow the circuit.

[wraper]

Nice fake Sanyo capacitor. Dunno if you soldered it in reverse or it was mislabeled but never buy capacitors on ebay, aliexpress or DX. FYI Sanyo branded capacitors are not made since around 8 years ago. They are called SUNCON now, and Sanyo/SUNCON don't have X style vent.

[cvanc]

(squints at photos again)  Yeah, probably a fake capacitor... note also the strange coppery colored leads.  Weird.

And I can 2nd the idea of incorrect silkscreening on a PC board, I've seen that too.

[Nerull]

The Amiga CD32 came from the factory with not only reversed silkscreen, but reversed capacitors too.