On Sat, 24 Nov 2012 12:42:17 -0800 (PST), KenO
put finger to keyboard and composed:

A very good test you can do is to check a zener diode with your multimeter set to the ohmmeter setting.

This is a simple test we can do to check whether it is good, open, or shorted.

What readings did you find? Did you also measure the resistance of R?
Note that when performing resistance measurements, you need to do so
in the absence of power.

To answer your other questions, I use isopropyl alcohol to clean PCBs
but I'd be wary of using it on device markings. Sometimes they rub
off.

The markings on the zener usually reflect its breakdown voltage.

The battery appears to have three cells. Is it a 3.6V type? Does it
have a mAH rating on the body?

I notice that there appears to be extensive galvanic corrosion at the
switch terminals. I expect that the associated copper traces may
eventually turn black.

- Franc Zabkar
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