Then the other side of the filter (Capacitor's (+) and other side of resistor) goes to pin 4 of the 4N25 and to pin 5 of LM3914.
Then the 5V wires that are to all of the leds (+), to the LM3914's pin 3, and also to its pin 9 (via the optional jumper).
Finally you must ensure all IC pins are well connected, including pin 1 of LM3914 to the first led.
When you're done soldering, secure the LM3914, but instead of placing the optocoupler, short its pins 4 and 5 on the socket. Using the external AT power supply and turn it on. If all is OK, you'll see your leds dimming ON from the first to the tenth. If you don't have LEDs to turn on, you might have done something wrong soldering the LM3914 or the leds. You can verify all connections using a multimeter, and verify there's no short circuit anywhere.
Click to Enlarge
It is time to test with your HDD led indicator header. Normally with HDD activity you should see it passing from led 1 to 10 depending on disk usage. If you don't have this, you might simply have placed the HDD led header backwards, in which case inverting them will be fine, or you can have either burnt you optoisolator, or have a defective one. I had a defective 4N28 - what it did was spanning from 1 to 2 LEDs, so the internal transistor should have been corrupted. I replaced with a 4N26 which yielded success.
Take a look at it in action here! (1.6MB .avi)
These are the 2 high-tech DIY eye-candies to transform your HDD led indicator into a HDD usage level indicator. I hope you enjoyed this mod as much as I enjoyed doing it. If you have problems with any of those 2 projects, head on over to GTF, I can surely give you a hand. Good luck and enjoy the show!