outdoor motion detector light failure

Our house has an outdoor PIR motion detector that turns on a couple of lights. It works fine most of the time, but it fails when the weather has been rainy for a couple of days. The symptom is that the monitor LED flashes when it sees motion (so the PIR detector is still working) but the lamps never come on. At first glance, it looks like the circuit still thinks it is daylight (there's a CdS photocell to detect ambient light).
My guess is that either the photocell has become moisture-sensitive, or the circuit board has built up enough crud to provide a low-resistance path across the photocell when it gets damp. Has anyone seen this behaviour and fixed it before?
If the board is just dirty, cleaning it and perhaps adding some conformal coating to the board should fix it. If the photocell is bad, it will have to be replaced. Or should I just toss the whole thing and replace with new? It's mounted high above the garage door, so it's somewhat of a pain to get at, particularly when it is raining (and when the weather is good, it works fine).
It's a Heath/Zenith model. There are a couple of mode switches on the bottom as well as a sensitivity adjustment, so the case is not sealed.
    Dave
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On Mon, 22 Oct 2007 20:43:09 +0000 (UTC), snipped-for-privacy@cs.ubc.ca (Dave Martindale) wrote:

One thing you can try is to operate all the pots and switches several times to clean them a bit. At a certain point it is easier to just toss it, particularly if it is hard to get to.
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At first glance, it looks like the circuit

I've R/R'ed the photocell on one of these, and it did the trick. Actually it's a photoresistor, and Radio Shack used to (and still might) sell an assortment of them for a few bucks. It lasted a few more years anyway.
I don't think it matters much if the photoresistors are a match -- it didn't in my case.
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snipped-for-privacy@cs.ubc.ca (Dave Martindale) wrote:

PIR lights are pretty cheap these days. I'd just replace it...
-- "Tell me what I should do, Annie." "Stay. Here. Forever." - Life On Mars
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