RE: Checking M.O. diodes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" <deano-at-corridor-dot-net>

Hi

In working on Microwave ovens in the field for several years, (commercial
kitchen equipment repair)  it was necessary to find a quick and dirty test
to find out the condition of the diodes. Most guys used the cheap go/ go
tester offered to the trade which had a 9 Volt battery and a small light
bulb. It would tell you if the diode would conduct in one direction or not,
but would give no indication as to the condition of the junctions. I used a
9 Volt battery in series with a 10M Ohm input impedance voltmeter in series
with the diode in question. Subtract the meter reading from the battery
voltage to get the forward voltage drop. The drop should be around 4.5 to 5
volts across the diode. Sometimes they will have a shorted junction and read
lower. In that case the diode will still work, but will not last long, and
can cause other problems. This value is valid for Amana Microwaves. Other
brands will have different diodes which may give different readings. The
best thing to do is to take _your_ meter and _your_ battery and a _new_
diode of the same type and get a reading to see what it is supposed to be
for that particular diode. Then you can compare the suspect diode. If it has
a shorted diode inside it, it will read about 1/2 volt lower than it should.
If more than one diodes are shorted, the voltage will be lower by about .5
times the number of shorted sections.  This is the best quick and dirty
method I have found that gives meaningful results (as opposed to the go / no
go test) which can be implemented in the field with stuff normally carried
in a tool bag.

later
deano

> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Wednesday, January 31, 2001 9:14 PM
> To: tesla-at-pupman-dot-com
> Subject: Checking M.O. diodes
>
>
> Original poster: "J. B. Weazle McCreath by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <weazle-at-hurontel.on.ca>
>
>
> Hello coilers,
>
> Anyone have a proven method for checking microwave oven diodes?
> My VOM, even on its highest ohms scale, won't show continuity
> in one direction as it does on "ordinary" (1N4007) type diodes.
> I tried measuring a known good diode, but no luck there either.
>
>
> 73, Weazle, VE3EAR/VE3WZL
>
> Listening: 147.030+ and 442.075+
> E-mail:    weazle-at-hurontel.on.ca
>            or ve3ear-at-rac.ca
> Web site:  www.hurontel.on.ca/~weazle
>
>
>