Hi,
I just bought this Daiwa.....
Hopefully it works?
They are made of a pickup coil, wire, a meter, a switch, adjustable resistors for internal tuning, and 1N34 germanium detector diodes. Rarely, a diode might fail. Rarely. Or the switch gets dirty or wears out. Variable resistors might get dirty. Meter might get sticky/stuck. Can't think of any other problems.
What I described there is a passive type meter. It is fine for checking SWR; but not necessarily accurate for reading true peak power. True peak power meters have more circuitry involved. Which requires a small amp circuit to be able to make the meter move when weak parts of the signal need to be made large enough to move the meter. That is how they differ from passive-type meters. Doesn't mean passive meters aren't accurate for SWR - they are; but not really accurate for honest peak power readings. Fine for testing dead key power; but as much as 10% less for showing peak envelope power ('PEP') readings. Just a FYI . . .