Does anybody know how to tell what kind of diode this is? I know it is a
zener diode, but thats about all I know..
Here is a picture
http://mikescomputer.homeip.net/LCD/DSC00382.JPG
It is at ZD1

Thanks in advance,

- Mike

"Michael Kennedy" wrote in message
...
Does anybody know how to tell what kind of diode this is? I know it is a
zener diode, but thats about all I know..
Here is a picture
http://mikescomputer.homeip.net/LCD/DSC00382.JPG
It is at ZD1

Thanks in advance,

- Mike

The stripes look grey and red, so I guess that might make it 8V2, which is a
standard zener value.

Arfa

Well there is a black stripe in the middle does that matter?
I enlarged the picture.
http://mikescomputer.homeip.net/LCD/ZD1.JPG

Is this color chart I found correct?
http://www.oldradios.co.nz/data/index5.htm

Thanks,
-Mike



"Arfa Daily" wrote in message
...

"Michael Kennedy" wrote in message
...
Does anybody know how to tell what kind of diode this is? I know it is a
zener diode, but thats about all I know..
Here is a picture
http://mikescomputer.homeip.net/LCD/DSC00382.JPG
It is at ZD1

Thanks in advance,

- Mike

The stripes look grey and red, so I guess that might make it 8V2, which is
a standard zener value.

Arfa

" "Michael Kennedy" wrote in message
...
Does anybody know how to tell what kind of diode this is? I know it is a
zener diode, but thats about all I know..
Here is a picture
http://mikescomputer.homeip.net/LCD/DSC00382.JPG
It is at ZD1

Thanks in advance,

- Mike

The stripes look grey and red, so I guess that might make it 8V2, which
is a standard zener value.

Arfa



"Michael Kennedy" wrote in message
...
Well there is a black stripe in the middle does that matter?
I enlarged the picture.
http://mikescomputer.homeip.net/LCD/ZD1.JPG

Is this color chart I found correct?
http://www.oldradios.co.nz/data/index5.htm

Thanks,
-Mike

Is that black stripe a genuine paint one on the outside of the diode, or a
"ring of fire" where it's failed ? It's right over where the actual diode
inside is. I'm assuming that it has failed short-circuit or whatever,
otherwise, you'd be able to just measure the voltage across it ?? I'd still
have money on it being 8V2 as this is such a common value. Are there no
other indicators as to what voltage it is ? Voltage that it's zenering down
from, value of series reistor, working voltage of any following
electrolytics, markings on the board of power supply voltages etc ??

The chart appears to be correct.

Arfa

Is that black stripe a genuine paint one on the outside of the diode, or a
Yes I believe it is genuine paint. It is on the other diode which has not
failed.. I guess I could find out what kind of zener diode it is by testing
it as you said, but I have never done this before.. I guess it is time to
learn.

Here is a picture of the working diode (ZD2 not ZD1) up close and in the
sun so you can really see the colors..

http://mikescomputers.homeip.net/LCD/DSC00386.JPG

Close-Up

http://mikescomputers.homeip.net/LCD/ZD2.JPG

Thanks,

- Mike

"Michael Kennedy" wrote in message
...

Is that black stripe a genuine paint one on the outside of the diode, or
a
Yes I believe it is genuine paint. It is on the other diode which has not
failed.. I guess I could find out what kind of zener diode it is by
testing it as you said, but I have never done this before.. I guess it is
time to learn.

Here is a picture of the working diode (ZD2 not ZD1) up close and in the
sun so you can really see the colors..

http://mikescomputers.homeip.net/LCD/DSC00386.JPG

Close-Up

http://mikescomputers.homeip.net/LCD/ZD2.JPG

Thanks,

- Mike


OK. Looks like a genuine paint band. I'm still up for it being 8V2 though,
if for no other reason than it's a very common value, and corresponds to the
other two stripes. If what ever the unit is, is working at all, then just
check the voltage across the non-blown diode. If the unit is not working,
you can test the other diode for voltage rating easily enough, by removing
it from the board and hooking a resistor - say 4k7 - to its cathode. Then
put 12v across the combination, "+" to the free end of the resistor, "-" to
the diode's anode, then measure the voltage across the diode. Any reading up
to about 11v, will be the zener voltage. If you get a reading of 11v or
more, then the diode hasn't 'zenered' and you need to up the voltage across
the combination a couple of volts at a time, until you do get a steady
voltage, that doesn't increase any more, as you continue to up the voltage.
You've then found the diode's zener voltage.

Arfa

I was at the local surplus dealer and they had the zener diodes organized by
zener voltage. Would a 8v2 be a 8.2v zener?
Thats what I got and it seems to ohm very close to what the good zener ohms.

The actual part number for the zener that I got is 1N5237b738.

Thanks for all the help Arfa

- Mike

"Arfa Daily" wrote in message
...

"Michael Kennedy" wrote in message
...

Is that black stripe a genuine paint one on the outside of the diode, or
a
Yes I believe it is genuine paint. It is on the other diode which has not
failed.. I guess I could find out what kind of zener diode it is by
testing it as you said, but I have never done this before.. I guess it
is time to learn.

Here is a picture of the working diode (ZD2 not ZD1) up close and in the
sun so you can really see the colors..

http://mikescomputers.homeip.net/LCD/DSC00386.JPG

Close-Up

http://mikescomputers.homeip.net/LCD/ZD2.JPG

Thanks,

- Mike


OK. Looks like a genuine paint band. I'm still up for it being 8V2 though,
if for no other reason than it's a very common value, and corresponds to
the other two stripes. If what ever the unit is, is working at all, then
just check the voltage across the non-blown diode. If the unit is not
working, you can test the other diode for voltage rating easily enough, by
removing it from the board and hooking a resistor - say 4k7 - to its
cathode. Then put 12v across the combination, "+" to the free end of the
resistor, "-" to the diode's anode, then measure the voltage across the
diode. Any reading up to about 11v, will be the zener voltage. If you get
a reading of 11v or more, then the diode hasn't 'zenered' and you need to
up the voltage across the combination a couple of volts at a time, until
you do get a steady voltage, that doesn't increase any more, as you
continue to up the voltage. You've then found the diode's zener voltage.

Arfa

Zener would have failed for a reason.
If you replace it most likely the new one will go that way too.

Peter


"Michael Kennedy" wrote in message
. ..
I was at the local surplus dealer and they had the zener diodes organized
by zener voltage. Would a 8v2 be a 8.2v zener?
Thats what I got and it seems to ohm very close to what the good zener
ohms.

The actual part number for the zener that I got is 1N5237b738.

Thanks for all the help Arfa

- Mike

"Arfa Daily" wrote in message
...

"Michael Kennedy" wrote in message
...

Is that black stripe a genuine paint one on the outside of the diode,
or a
Yes I believe it is genuine paint. It is on the other diode which has
not failed.. I guess I could find out what kind of zener diode it is by
testing it as you said, but I have never done this before.. I guess it
is time to learn.

Here is a picture of the working diode (ZD2 not ZD1) up close and in
the sun so you can really see the colors..

http://mikescomputers.homeip.net/LCD/DSC00386.JPG

Close-Up

http://mikescomputers.homeip.net/LCD/ZD2.JPG

Thanks,

- Mike


OK. Looks like a genuine paint band. I'm still up for it being 8V2
though, if for no other reason than it's a very common value, and
corresponds to the other two stripes. If what ever the unit is, is
working at all, then just check the voltage across the non-blown diode.
If the unit is not working, you can test the other diode for voltage
rating easily enough, by removing it from the board and hooking a
resistor - say 4k7 - to its cathode. Then put 12v across the combination,
"+" to the free end of the resistor, "-" to the diode's anode, then
measure the voltage across the diode. Any reading up to about 11v, will
be the zener voltage. If you get a reading of 11v or more, then the diode
hasn't 'zenered' and you need to up the voltage across the combination a
couple of volts at a time, until you do get a steady voltage, that
doesn't increase any more, as you continue to up the voltage. You've then
found the diode's zener voltage.

Arfa

"Michael Kennedy" wrote in message
. ..
I was at the local surplus dealer and they had the zener diodes organized
by zener voltage. Would a 8v2 be a 8.2v zener?
Thats what I got and it seems to ohm very close to what the good zener
ohms.

The actual part number for the zener that I got is 1N5237b738.

Thanks for all the help Arfa


Yes, 8V2 is eight point two volts. It is the de facto way of writing it
these days - at least this side of the pond - and saves any confusion with
flies crapping on the page, or your glasses needing replacement. It is very
easy for a decimal point to disappear as a result of poor printing, or one
to appear because of that fly ...

It is also the standard way of writing resistor values - 4k7, 1M2 for 4.7k
or 1.2M ( see how easily that 4k7 could be read as 47k ). Capacitor values
appear like this too. 6u8 for 6.8uF, 2n7 for 2.7nF, 0u1 for .1uF, 3p3 for
3.3pF etc. On some schematics, you will find voltage checking points marked
in the same way.

The resistance of a zener diode, is no indication of its zener voltage,
however. There are some exceptions, but in general, any small low voltage
zener will read the same, ohms-wise, as any other, and indeed, any other
ordinary diode, because this is all that they actually are. All diodes
exhibit zener effect when reverse biased. It's just that with zeners, the
doping of the semiconductor material has been calculated to produce
predictable and accurate reverse breakdown voltages.

Arfa

"Peter" wrote in message
...
Zener would have failed for a reason.
If you replace it most likely the new one will go that way too.

Peter


In 35 years of being in this business, I don't believe I can think of more
than a very few instances where a small zener diode has failed for any
reason other than poor design of the circuit that it's in, or just chance
failure. Very occasionally, a zener is placed across a supply rail as an
overvolt protection mechanism, and will fail if that rail rises much beyond
its nominal value - because of a failed series pass transistor, perhaps -
but normally, these are large 1 watt types, that will stand going short
circuit without exploding first, not little glass surface mount types, like
the OP's example. Also, rarely, a zener in a conventional regulator driver
stage, will fail if the transistor that it's connected to, goes
collector-base short, but this is a comparitively rare failure mode for
transistors.

I think that it is highly unlikely in this particular case, that there will
be any problem, other than the diode itself.

Arfa

I tested the good diode on a 12vdc transformer. The transformer had an
output of 16.7v and the diode "zenered" at 11.75v... so does that mean it is
a 12v zener?

- Mike

"Arfa Daily" wrote in message
...

"Michael Kennedy" wrote in message
. ..
I was at the local surplus dealer and they had the zener diodes organized
by zener voltage. Would a 8v2 be a 8.2v zener?
Thats what I got and it seems to ohm very close to what the good zener
ohms.

The actual part number for the zener that I got is 1N5237b738.

Thanks for all the help Arfa


Yes, 8V2 is eight point two volts. It is the de facto way of writing it
these days - at least this side of the pond - and saves any confusion with
flies crapping on the page, or your glasses needing replacement. It is
very easy for a decimal point to disappear as a result of poor printing,
or one to appear because of that fly ...

It is also the standard way of writing resistor values - 4k7, 1M2 for
4.7k or 1.2M ( see how easily that 4k7 could be read as 47k ). Capacitor
values appear like this too. 6u8 for 6.8uF, 2n7 for 2.7nF, 0u1 for .1uF,
3p3 for 3.3pF etc. On some schematics, you will find voltage checking
points marked in the same way.

The resistance of a zener diode, is no indication of its zener voltage,
however. There are some exceptions, but in general, any small low voltage
zener will read the same, ohms-wise, as any other, and indeed, any other
ordinary diode, because this is all that they actually are. All diodes
exhibit zener effect when reverse biased. It's just that with zeners, the
doping of the semiconductor material has been calculated to produce
predictable and accurate reverse breakdown voltages.

Arfa

"Michael Kennedy" wrote in message
. ..
I tested the good diode on a 12vdc transformer. The transformer had an
output of 16.7v and the diode "zenered" at 11.75v... so does that mean it
is a 12v zener?

- Mike

That would certainly indicate a 12v zener. This is another very commonly
found value.

If that is the case, then the coloured bands on this particular diode, would
seem to be meaningless. unless they are signifying a diode type that
contains the numbers " 802 " or " 208 "
or it's some kind of house code. If the voltage definitely settled at
11.75v, with a 4k7 series resistor, then the only other check that I might
do, if it was me, would be to drop the value of the series resistor to
perhaps 2k2, to increase the zener current. Sometimes, a zener will not
stabilize to its nominal rated voltage, if the zener current is too low. If
you still get around the same voltage, then you can assume that 12v is the
correct value.

Arfa