Can anyone check their IIfx for C27?

[Johnnya101]

Hi guys,

Want to get my IIfx Recapped, and C27 was so rotted it fell off! That was last year, and it's been in storage. Now's the Time im finally getting to it, and don't know where I out the one that fell off.

Anyone have a IIfx that's willing to check what it is? It's right on the right side of the board when you take off the cover.

 

[AlpineRaven]

47uf 16v I think?

Cheers

AP

 

[Johnnya101]

Oops, got the wrong one. I need C24! Silver can. The labels are right next to each other.

Alpine, that is correct for C27 though!  Thats the radial.

 

[360alaska]

look over here: 

 

[Johnnya101]

Thank you Alaska, but I dont seem to see it in there. i see C27, but not 24.

 

[360alaska]

Page 1 of the Bomarc schematic or...... this:

 

[Johnnya101]

Oh, ok, see it now. It appears to be 47 uf as the other can on the board. Now I just need a voltage to go off of... It is probably 16, like the other, but im not taking any chances.

 

[LaPorta]

Just throw in a 25 or 50

volt. It will likely last longer, to boot.

 

[Jinnai]

All SMD capacitors in Macintoshes are 16v 47uF  

 

[Johnnya101]

Cool, thanks guys

 

[Franklinstein]

All SMD capacitors in Macintoshes are 16v 47uF  

Not quite, but it does seem that value comprises the vast majority of them in desktops, anyway. Other common values are 100@6v, 100@16v, 22@16v, 22@25v. PowerBooks will often have these and more, such as 330@25v or 470@50v in the power supply sections.

Rule of thumb with capacitors: in a pinch you can usually go up a value or two, but never down. So a 100@25v could be installed in place of a 47@16v, if it physically fits. Substitution isn't something you'd want to do habitually, but it doesn't hurt to do so occasionally if you know what you're doing.

*all values in micro Farads/uF

 

[trag]

1uF @ 50V and 10uF @? (16, 20V?) are also common.    Well, the SE/30 uses a single 1uF cap and the SE/30 is common.    The IIci has a couple of 10uF caps, but the LCs and Color Classic and such are full of them.

For bypass capacitors (capacitors sitting across the power and GND) lines, you can vary the values as Franklinstein writes without much affect.     And in almost all cases you can raise the Voltage rating of the cap without problems.   For capacitors that are part of a frequency dependent circuit or a timing circuit, changing the capacitance could strongly affect behavior.

Qualify the above with the observation that the average capacitor is built with a 20% tolerance.  So, unless precision capacitors were used in the hypothetical timing/frequency dependent circuit mentioned above, the capacitor may already be as much as 20% above or below its listed value.    

The only reason why using a capacitor with a higher voltage rating might affect the performance of the circuit is that getting a higher voltage rating often affects the internal resistance/impedance of the capacitor.