0

My arduino has these two capacitors

enter image description here

But I can't find any 47uf capacitors on the schematic. Is this not the value but instead a code? Where are these in the schematic?

enter image description here

2
  • I don't know why you are concerned, but if you had an up-to-date schematic you would see them. They are exactly where you would expect to see them- around the 5V regulator. – Milliways Mar 29 '15 at 10:59
  • 1
    I'm not concerned, I'm learning. I was just wondering if I was missing something or most of the schematics online don't show them for some reason. – Ryan Detzel Mar 29 '15 at 11:10
4

What: Looking at the schematic that you provided, it seems likely that they serve as C6 & C7.

Why: These are shown as 100 uF each and act as "filter" capacitors for IC4, the 5V regulator.
Within certain limits, such capacitors are not critical in value, and the manufacturer has probably decided that a factor of in the capacitance is probably acceptable.
They are probably correct :-).

How to check: You can check this yourself with an Ohm-meter set to the lowest Ohm range available - often = 200 Ohms max.

Turn off power to the board and leave it off for say 5 minutes to allow capacitors to discharge.
Locate I4 and find its input and output pins or tracks leading to them. You can often get ohmic connections at vias as the tracks change board layers.
IC4 pin1 will be grounded.
One lead of C6 & C7 are also grounded.
The pad you can see in your photo on the board edge side of the caaps is probably the -ve terminals (about 99%+ likely) (and they match the can markings) and the "stippled" surface is almost certainly system ground.

If you can confirm that the two caps are connected to ground as and where described above, then:

Apply Ohm meter probes between the non ground lead of a capacitor and each non-ground pin in turn of IC4. One of them will be a low resistance connection if they are C6 & C7. Check the other capacitor - it should connect to the other side of IC4.
Reversing the meter leads in each case may give somewhat different readings for non-hard-connected points but should be low and consistent for hard-connected by a track points.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.