"mick" wrote in message
eb.com...

I've got quite a few of these. They look like 1N400x family but are
marked W642G1, with 540 on a second line. I've been using them as '4001s
but they may well be something else. The W symbol has vertical sides, by
the way. It could be a logo.

If you check Vf on a DMM diode check, generally speaking the lower the Vf -
the faster the rectifier - then there's the jump to the much lower Vf of SB
rectifiers. If you get a Vf measurement actually anywhere near 0.7V, its
likely to be a zener.

You can check reverse breakdown voltage with a (2 electrolytic) voltage
doubling bridge rectifier fed by a high resistance (about 68k for 230V) and
monitor the slow voltage rise until it stops, with a DMM.

The fully charged electrolytics are of course pretty dangerous - if you just
add a shorting switch to discharge the capacitors, it will blow the contacts
away - put a NTC surge limiter in series with the switch.