varicap diode testing?

A varicap is just an ordinary diode. When reverse biased, it acts as a capacitor which varies with the applied reverse bias. It never conducts current in the forward direction. Never... Ever...

No.

I have no idea. Perhaps it would be helpful if you would disclose:

1. What are you trying to accomplish?
2. What are you working on? (Make and model)?
3. What have you done so far and what happen?

Thanks for reply this is a photo of the outdoor part of the wireless thermometer that stopped working

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You expect anybody to get even the faintest idea of what that 'picture' is? You DID replace the batteries on both the transmitter and receiver, right?

G=B2

Blurrrrrrry useless photo. Try again, this time with the camera set to macro, and without the drastic tilt angle, which requires too much depth of field.

Nope. See my 3 questions.

I've had far too much entertainment with wireless weather stations. They don't seem to fail, but they do drift off frequency, or lose power output due to moisture absorption in the PCB. I cheat and use a spectrum analyzer to look at what it's sending. To the best of my knowledge, most such remote thermometers do not use a varicap. However, the humidity sensor is a polyimide or polystyrene capacitor, with no case. The capacitor changes value as the dielectric absorbs moisture and swells.

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thanks the 'varicap' mentioned then might be a temp sensor(no humidity) as for frequency (589M says on the box)drift adjusting the screw near top of pic1 did not help I wonder where is the antenna input please se

It's not a varicap. The thermometer element is either a thermistor, or a semiconductor, such as an LM335:

There are also thermometer chips that have the sensor inside:

The previous photo was blurry. These two are both blurry and too small. Looks like you're using a Blackbery 8100 camera phone. Few camera phones take decent closeup photos. Try using a real digital camera with a "macro" setting.

See my 3 questions.