I found myself once again doing some EcoQuest Fresh Air II air purifier repairs. One of ours quit making ozone. I opened it up but could not find the problem. After looking at it several times and getting ready to salvage parts and toss it, I then discovered that R11 was toast. Checking the FET, a 10N20L showed that it was shorted!
I disconnected the 10N20L by clipping the leads and it was still shorted. R11 was toast and there was no way to find out its value. Unfortunatly I threw out my spare board! Oops.
I could not find a 10N20 but did find a IRF630 that has similar specs and used that. The drain is connected by the case but the replacement will not solder to the board so you will need to run a small jumper wire. A 4.7 ohm one watt resistor will work for R11 as it was a current limiter resistor (I think).
So it has been up and running for a couple of hours now with no problems.
