I'd start by poking around with your multimeter. Check the PWM pin to see what the output is and make sure you haven't accidentally reversed the ground and PWM wires, then start checking each part of your fan circuit. If I remember that crazy-assed circuit correctly, there is a chance the transistors aren't saturated and thus aren't acting like switches as they were intended to.

Also, check the programming to see what the minimum and maximum PWM outputs are. Most fans will struggle to operate properly once the PWM drops below a certain duty%.

Finally, make sure your controller and fan circuit are sharing the same ground (not just plugged into the same circuit but literally have their ground planes connected). If they aren't I can almost guarantee that's the problem.

Everything looks like it checks out. But it turns out the BC549C can't power up multiple fans so the 2N3904 that is on that schematic Chris shared earlier. There's a thread on ukreefs about it but not sure if I can link it here...

Can you repost the schematic and the link to that thread so I can take a look?

Sure
Schematic:
http://i1177.photobucket.com/albums/...ps8d293992.jpg


Link: You may have to go back 2 pages I think to where the guy brings up his problem and works through it.

http://ukreefs.com/index.php?topic=605.135


Thanks Chris for the help! Even though I kept you up 'till all hours of the morning on the east coast :D

Hmmm, looking like I have a wee bit of bleed voltage on my OCW string. On one heatsink, one of the OCW all 3 LED's are faintly lit and on the next in the series 2/3 LED's are lit.
http://i1177.photobucket.com/albums/...ps25d59256.jpg


Wheeeee, isn't DIY fun! :frusty:

Due to work and a project my wife asked me to do I've not been able to do anything on this project. I've ordered different transistors for the fan circuit and it's on it's way from China...

Pinhead: I tried returning your PM but your box is full.

Well, got all my proper parts from China for the Fan pwm control to build it exactly as per drawing above, and the PWM speed control still doesn't work... argh.

Gonna resurrect this. It's going to be the only thing holding me back from my tank upgrade soon. I built another circuit board to exactly match the one in post #214 last night. Plugged 'er all in this morning with one heatsink and it's doing to the same thing. Heatsink temp is at 38.6C and the fan hasn't ramped up. It's still running at the same speed it had started at. Maybe something in the sketch...

Lol, ok, I'm an idiot. I was wracking my brain thinking of anything that could be the problem. The fan still hasn't been ramping up and down via the PWM signal according to the temp sensor on the heatsink. I have a DS18B20 sensor that looks like a BC549 transistor, sunk into my heatsink with thermal compound and that's controlling my fans. I also have another one that is attached to a cable and sealed in an encased water proof housing like in your manual.
So I wondered if it was working properly. As soon as I grabbed it and watched the temp on the monitor go up, I realized the fan was speeding up :D
Duh, I must have either screwed up the pin assignments or something. It's been a long while since I set this all up, so I have to go back and read in the manual what's making all this work.
But at least I've got an idea what's wrong now! LOL
I haven't fixed it yet, but I'm still relieved.

Dude... no idea what you just said, might as well be speaking Swahilli... does it go beep beep like R2-D2? Lol.

Honestly though, I'm glad you figured it out. Are you going to be using this on your new build?