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Does anyone know the value of this capacitor?

Posted: Sun Apr 30, 2017 1:33 pm
by coolstuff
http://imgur.com/a/xY4rZ

Its capacitor c106, thanks

Re: Does anyone know the value of this capacitor?

Posted: Sun Apr 30, 2017 2:10 pm
by mahjongg
full schematics of the PI3B have not been released, and C106 doesn't appear in the reduced schematics, so nobody can help you.
I looked in the schematic of the PI2 B but C106 also does not exist in a PI2B.
I guess C106 has something to do with USB current limitation and might not be critical, I would simply try if a 100nF cap works.

Re: Does anyone know the value of this capacitor?

Posted: Sun Apr 30, 2017 2:22 pm
by gregeric
The component numbering seems to be retained with newer Pi versions.

Previously, mahjongg has confirmed C106 as 220nF on a B+. I'd be confident that is still the case on a Pi3. It's likely the exact value won't matter anyway if it's a decoupling capacitor, and may even work without it.

Edit: it def is there on a Pi2, to the left of D3 on the PCB around the USB current limit circuitry.

Re: Does anyone know the value of this capacitor?

Posted: Sun Apr 30, 2017 2:38 pm
by mahjongg
ah yes indeed, I looked in the schematic of the PI1 revision 2.1, and obviously it doesn't have the USB current limiter.
But yes I have previously found C106 to be 220nF, indeed in the current monitor.

I agree that the RPF does not seem to renumber previously used components in new schematics.

Re: Does anyone know the value of this capacitor?

Posted: Sun Apr 30, 2017 2:59 pm
by coolstuff
Awesome, thanks. So, to be clear, the pi can work without it?

Re: Does anyone know the value of this capacitor?

Posted: Sun Apr 30, 2017 3:12 pm
by gregeric
Well in this case it seems to be part of an RC time constant / delay, not decoupling - see Burngate's diagram in the link I gave.

It's there so that the current limiting switch can be turned on quickly via the diode, but turned off with a delay while discharging through the resistor. Why that behaviour is needed eludes me right now!