Quadro FX 3000 - Identifying missing cap

[sebz1337]

Hi,

I've recently bought a used Quadro FX3000, and noticed that there was a missing SMD capacitor on the back of the card, as pictured below :



Does anyone know the purpose / specs of this capacitor ?

Thanks !

[Behemot]

Re: Quadro FX 3000 - Identifying missing cap

It's big so high capacitance. Plug it in and carefully measure voltage there, than select 6.3 V or 16 V depending on what you measure. X7R, highest capacitance you can find in that size.

[R_J]

Re: Quadro FX 3000 - Identifying missing cap

It's a ceramic cap. like others on the board, I guess you could measure one of the others, maybe .1 or 1uf
Heres a picture

[cpt.charlie]

Re: Quadro FX 3000 - Identifying missing cap

It's a "big" cap, maybe 10 or 22uF, try to desolder one of the others and measure.

[Behemot]

Re: Quadro FX 3000 - Identifying missing cap

It does not matter how much it is, just get the voltage and put the biggest one which fits. Filtering, the bigger the better. The card is at least a decade old, new ceramics greatly improved the volume capacity.

[sebz1337]

Re: Quadro FX 3000 - Identifying missing cap

Alright, I'll report back when I'll have the time to do some measurement!

Will it be bad for the card to operate without this capacitor (short / long term side effects) ?

[mariushm]

Re: Quadro FX 3000 - Identifying missing cap

Desolder one of the capacitors that look similar in size , like C535 for example, then measure the capacitance with a multimeter. (add solder to the ends and then as you heat up from both sides it will come off)

If you measure it in circuit, the value may be wrong because sometimes the capacitors are in parallel.

Once you get the capacitance you need to buy such a capacitor but with higher than normal voltage rating.

If it's on the input, the AGP slot works with 1.5v and 3.3v so the voltage rating would have to be higher... but I suspect they're on the output of a buck (dc-dc converter) that converts the input voltage to some lower voltage (for powering memory chips or the chip itself), so basically the voltage would be less than 1.8v (if it's memory) or less than 1.2v (if it's gpu chip). The reason i suspect that is the presence of that diode D506 so close to the ceramic capacitors.

So in theory you can use 4v rated or higher ceramic capacitors, but in practice ceramic capacitors drop significantly in capacitance as the voltage on them increases. So for example, a 10uF 10v ceramic may only have about 4-6 uF of capacitance with 5v on it.

So even if the voltage is so low, you would have to pick some ceramic capacitor rated for at least 16-25v, otherwise the actual capacitance would be much lower.

I think X7R capacitors of high capacitance and high voltage would be expensive.. I think even X5R would be reasonable here. It may be cheaper for you to buy 2 ceramic capacitors of lower capacitance and populate those two if they're in parallel.

For example a 10uF 25v x7r may be 1$ but you could get 2 x 4.7uF 25v x7r for 0.2$ each.