Hi! I have some surface-mount capacitors I need to replace. I don't really understand the codes on them, despite looking up many sets of SMD capacitor coding conventions on the net. Is the first number the capacitance value or is the second number? If someone could help decipher the values, I'f be very grateful. Thank you in advance. One of them has this printed:
h3
Another:
In these cases it looks like the second number is the capacitance (in uF) but I can't be sure. Are these tantalum capacitors (relatively high capacitance, with a positive end marked)?
I was thinking the second number is the capacitance also, but I wasn't sure if possibly the first number is a multiplier for the second number. These are small, silver-coloured, cylindrical components apparently with an aluminum casing, about 1/4-inch in diameter and about 3/16-inch tall, having a thin, square plastic base and soldered directly to the surface of the board. There's a gray band striped down one end of them, on the top, where the numbers are. (Is this negative or positive?) Regarding the capacitance, I can't be sure until I understand how to read the numbers.
I'm replacing these because they're on a motherboard which has power-up/boot issues which have been gradually worsening, and some of these capacitors have bulges in the top of the casing. Doesn't this only happen with electrolytics, when the electrolyte fluid dries up, becomes a gas, and expands from the heat?
Thanks!
My guess would be 47 uF at 16V and 100 uF at 6V
You can get some sanity checking by finding a data sheet for a similar part and checking that those values come in the size cans that you have.
If you get lucky, you will find a data sheet that explains the marking that you have.
With the low working voltages, they're most likely electrolytics, and they are 47 uF and 100 uF.
A dark band on an electrolytic capacitor is normally negative. To find out for sure, power it up and use a voltmeter.
From your description it seems highly likely that they are aluminum electrolytics, and that the second number is the capacitance (in uF) and the third is the voltage.
Replace the caps with ones rated for 105C temperature - they'll last a bit longer.
I'm not sure which side the gray band is - I've seen both, in practice. Can you get at one of them with a voltmeter, when the power is turned on?
Yes, and I've seen tantalums where the positive was marked, but his description does sound like aluminums. But with the square base? It's the first time I've ever heard of a cap with a square base. Are you sure they're not transformers?
Thanks, Rich
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