White dot negative or positive

[mmaghakian]

I am working on two Audiosource AMP TWO amps and the board marking seem wrong
all the positive leads are marked with a white dot, I thought that meant negative. am I wrong ?
check out all three blue caps in the picture

 

[wrenchone]

I would think that you're wrong in this case. Especially as the (-) stripe on the capacitor jacket is on the opposite side of the white dot. I assume none of the caps vent when you apply power, so they are oriented correctly...

 

[mmaghakian]

but what is normal and customary design protocol ?

 

[wrenchone]

Whatever the manufacturer thinks it is. Accept it and move on.

 

[Refugee1]

It is quite common to get a batch of boards back from assembly contractors with all the caps the wrong way round.
The first unit to go on test is normally quite entertaining.
The remaining boards chucked back for re-work.

 

[rayma]

Just verify what the polarities should be for yourself. A schematic makes this trivial.

 

[vinylkid58]

A schematic makes this trivial.

Exactly! Guessing the OP doesn't have one.

jeff

 

[rayma]

If you don't have the schematic, measure the DC voltage across each electrolytic and compare with the markings.
I'd guess the dots indicate the positive leads.

 

[Mark Tillotson]

No idea why they didn't simply put a + sign instead of a blob, that would be unambiguous (for electrolytic capacitors at least).

 

[Hiten]

just guessing
May be the +ve and -ve sign gets confused with alphaneumeric text ? The white blob may also be of traditional assembly method/sequence of placing components. Or may be the assemblers are following old methods of markings and dont want to change. The Jumpers also has white blobs.

 

[Elvee]

The unwritten convention is that the marking sign (can be a blob, strip or anything else) is on the - side for wet Ecaps, and + for solid types, like tantalum.
When there is no explicit polarity mark visible, the right of the text is the positive and the left is negative.
The silkscreen of the PCB is probably suited to tantalum caps

 

[HalFoster]

Most HP test equipment, and several other manufacturers, uses a small dot on the solder side to indicate the positive terminal. While capacitors are typically marked as per @Elvee above, the PCB markings are just about always marked to show the positive terminal.

Hal

 

[egellings]

Probe it with a DC voltmeter and see which way it is.

 

[JMFahey]

just guessing
May be the +ve and -ve sign gets confused with alphaneumeric text ? The white blob may also be of traditional assembly method/sequence of placing components. Or may be the assemblers are following old methods of markings and dont want to change. The Jumpers also has white blobs.
View attachment 1309013

IF large caps and jumpers hace white dots, maybe they are assembly reminders.
Say 90% of board is machine assembled, and large or inconvenient componentsre later added by hand.
White dots help not missing one ore more by mistake.
Just thinking aloud.

 

[rayma]

Yes, the dots seem to be either reminders or check points.

 

[mmaghakian]

In this case it is interesting that all the BP caps also have a white dot at one lead

 

[elektryk]

It may not be a mistake. For example on Asus and Asrock computer motherboard positive lead is marked instead of negative one...

 

[mmaghakian]

now this is wild, I pulled out a smaller board to review for upgrading and the caps are installed in the opposite way... negative goes to the white dot (actually a white semi circle) side !

 

[wrenchone]

A white semicircle is a standard way of denoting the minus terminal on a capacitor - we have used that nomenclature in the past on our own capacitor outlines at my work place. Nowadays we just mark the plus side of the capacitor with a (+) sign.