Help me identifying a diode marking

[Apple_Tester]

Hi!
Short circuited diode, glass enclosure.
The only markings are 2 and 18.
Zener 18V?

 

[Apple_Tester]

IBM PS/2 85 server PSU, API manufactured

Diode #ZD1

It's a Zener for sure, since it's labelede ZD1.

 

[Tim Schwartz]

On 4/29/2014 8:30 AM, Apple_Tester wrote:

Hi!
Short circuited diode, glass enclosure.
The only markings are 2 and 18.
Zener 18V?

Hello,

If you could re-post, mentioning the make and model of the item the
diode belongs to, and the circuit location, it would help all identify
the part for you, as someone might have the schematic, and be able to
look it up.

Regards,
Tim
Bristol Electronics

 

[dave]

On 04/29/2014 07:58 AM, Tim Schwartz wrote:

On 4/29/2014 8:30 AM, Apple_Tester wrote:
Hi!
Short circuited diode, glass enclosure.
The only markings are 2 and 18.
Zener 18V?

Hello,

If you could re-post, mentioning the make and model of the item the
diode belongs to, and the circuit location, it would help all identify
the part for you, as someone might have the schematic, and be able to
look it up.

Regards,
Tim
Bristol Electronics

Can't you check a zener diode with a bench power supply and a couple
resistors?

 

[John Robertson]

On 04/29/2014 8:16 AM, dave wrote:

On 04/29/2014 07:58 AM, Tim Schwartz wrote:
On 4/29/2014 8:30 AM, Apple_Tester wrote:
Hi!
Short circuited diode, glass enclosure.
The only markings are 2 and 18.
Zener 18V?

Hello,

If you could re-post, mentioning the make and model of the item the
diode belongs to, and the circuit location, it would help all identify
the part for you, as someone might have the schematic, and be able to
look it up.

Regards,
Tim
Bristol Electronics


Can't you check a zener diode with a bench power supply and a couple
resistors?

Not if it is "short circuited". (ducking)

John ;-#)#

--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[Phil Allison]

"dave"

On 04/29/2014 07:58 AM, Tim Schwartz wrote:
On 4/29/2014 8:30 AM, Apple_Tester wrote:
Hi!
Short circuited diode, glass enclosure.
The only markings are 2 and 18.
Zener 18V?


If you could re-post, mentioning the make and model of the item the
diode belongs to, and the circuit location, it would help all identify
the part for you, as someone might have the schematic, and be able to
look it up.


Can't you check a zener diode with a bench power supply and a couple
resistors?

** Sure - but the OP has a **short circuit** one !!!

For replacement purposes, you must know what the original part is OR what it
should have been - cos one occasionally comes up against incorrect parts
fitted in PCBs and even incorrectly marked parts.


..... Phil

 

[Mark Zacharias]

"dave" <ricketzz@earthlink.net> wrote in message
news:I5WdnfHwENajX8LOnZ2dnUVZ_smdnZ2d@earthlink.com...

On 04/29/2014 07:58 AM, Tim Schwartz wrote:
On 4/29/2014 8:30 AM, Apple_Tester wrote:
Hi!
Short circuited diode, glass enclosure.
The only markings are 2 and 18.
Zener 18V?

Hello,

If you could re-post, mentioning the make and model of the item the
diode belongs to, and the circuit location, it would help all identify
the part for you, as someone might have the schematic, and be able to
look it up.

Regards,
Tim
Bristol Electronics


Can't you check a zener diode with a bench power supply and a couple
resistors?

OP said it was shorted...

 

[Tim Schwartz]

On 4/29/2014 12:33 PM, Apple_Tester wrote:

IBM PS/2 85 server PSU, API manufactured

Diode #ZD1

It's a Zener for sure, since it's labelede ZD1.

Hello all,

I came across this link:

http://john.ccac.rwth-aachen.de:8000/alf/ps2_85/

While it does not give a schematic, it does talk about the power
supply, and from what I see there is no 18V supply. (See the "Details
about main board" section)

Regards,
Tim
Bristol Electronics

 

[N_Cook]

On 29/04/2014 13:30, Apple_Tester wrote:

Hi!
Short circuited diode, glass enclosure.
The only markings are 2 and 18.
Zener 18V?

looks as though you will have to trace out enough of the circuit to
decide whether a zener of too low a voltage or too high a voltage will
cause colateral damage. Then suck it and see with some values starting
from the safe end and note what happens

 

[Jon Elson]

Tim Schwartz wrote:

On 4/29/2014 12:33 PM, Apple_Tester wrote:
IBM PS/2 85 server PSU, API manufactured

Diode #ZD1

It's a Zener for sure, since it's labelede ZD1.

Hello all,

I came across this link:

http://john.ccac.rwth-aachen.de:8000/alf/ps2_85/

While it does not give a schematic, it does talk about the power
supply, and from what I see there is no 18V supply. (See the "Details
about main board" section)

Well, it could be a "suicide diode", if the power supply regulation
fails, the diode quickly fails to short and either the PS goes
into overcurrent limit or blows up as it isn't limiting anymore.
Many cheap Chinese PS modules now use these suicide diodes
instead of a more traditional SCR crowbar circuit.

They actually have a special diode made for this purpose.

Jon

 

[N_Cook]

On 30/04/2014 23:52, Jon Elson wrote:

Tim Schwartz wrote:

On 4/29/2014 12:33 PM, Apple_Tester wrote:
IBM PS/2 85 server PSU, API manufactured

Diode #ZD1

It's a Zener for sure, since it's labelede ZD1.

Hello all,

I came across this link:

http://john.ccac.rwth-aachen.de:8000/alf/ps2_85/

While it does not give a schematic, it does talk about the power
supply, and from what I see there is no 18V supply. (See the "Details
about main board" section)
Well, it could be a "suicide diode", if the power supply regulation
fails, the diode quickly fails to short and either the PS goes
into overcurrent limit or blows up as it isn't limiting anymore.
Many cheap Chinese PS modules now use these suicide diodes
instead of a more traditional SCR crowbar circuit.

They actually have a special diode made for this purpose.

Jon

Would "suicide diode" be a valid term for searching within a supplier
site?. I've come across guaranteed VTS/diode failure to short and never
open, before , but not able to nail it down. Would you know of any
VTS/diode type number that is definitely made for this purpose?

 

[N_Cook]

On 01/05/2014 08:22, N_Cook wrote:

On 30/04/2014 23:52, Jon Elson wrote:
Tim Schwartz wrote:

On 4/29/2014 12:33 PM, Apple_Tester wrote:
IBM PS/2 85 server PSU, API manufactured

Diode #ZD1

It's a Zener for sure, since it's labelede ZD1.

Hello all,

I came across this link:

http://john.ccac.rwth-aachen.de:8000/alf/ps2_85/

While it does not give a schematic, it does talk about the power
supply, and from what I see there is no 18V supply. (See the "Details
about main board" section)
Well, it could be a "suicide diode", if the power supply regulation
fails, the diode quickly fails to short and either the PS goes
into overcurrent limit or blows up as it isn't limiting anymore.
Many cheap Chinese PS modules now use these suicide diodes
instead of a more traditional SCR crowbar circuit.

They actually have a special diode made for this purpose.

Jon


Would "suicide diode" be a valid term for searching within a supplier
site?. I've come across guaranteed VTS/diode failure to short and never
open, before , but not able to nail it down. Would you know of any
VTS/diode type number that is definitely made for this purpose?

TVS not VTS. I just tried an assorted set of search terms and yet again
have not found a datasheet for a named TVS, guaranteed (even if only to
some probability) to fail short circuit

 

[Jon Elson]

N_Cook wrote:

Would "suicide diode" be a valid term for searching within a supplier
site?. I've come across guaranteed VTS/diode failure to short and never
open, before , but not able to nail it down. Would you know of any
VTS/diode type number that is definitely made for this purpose?

No, that's my own description. Digi-Key part
SA5.0ALFCT-ND is a representative part, although not the one
I've seen in a particular power supply. (I can't find the
part number of that unit right now.)

Jon

 

[N_Cook]

On 03/05/2014 21:36, Jon Elson wrote:

N_Cook wrote:



Would "suicide diode" be a valid term for searching within a supplier
site?. I've come across guaranteed VTS/diode failure to short and never
open, before , but not able to nail it down. Would you know of any
VTS/diode type number that is definitely made for this purpose?
No, that's my own description. Digi-Key part
SA5.0ALFCT-ND is a representative part, although not the one
I've seen in a particular power supply. (I can't find the
part number of that unit right now.)

Jon

I still cannot find specifically stated , designed to fail short
circuit in any associated datasheet for that TVS. Of course any device
might fail short or even frequently fail short but I've still never
found any TVS designed and stated as such to fail short for safety
purposes, ie as you succinctly term such a theoretical device , a
suicide device

 

[Phil Allison]

"Nutcase Kook"

Jon Elson wrote:

Would "suicide diode" be a valid term for searching within a supplier
site?. I've come across guaranteed VTS/diode failure to short and never
open, before , but not able to nail it down. Would you know of any
VTS/diode type number that is definitely made for this purpose?
No, that's my own description. Digi-Key part
SA5.0ALFCT-ND is a representative part, although not the one
I've seen in a particular power supply. (I can't find the
part number of that unit right now.)



I still cannot find specifically stated , designed to fail short circuit
in any associated datasheet for that TVS. Of course any device might fail
short or even frequently fail short but I've still never found any TVS
designed and stated as such to fail short for safety purposes, ie as you
succinctly term such a theoretical device , a suicide device

** Semis like zener diodes and power transistors fail short when over
voltaged or overheated and the melted silicon chip does not repair itself.
So, the only way it can go open is if a feed wire fuses after the event.

Zeners ( even 400mW ones) have the chip fitted between a pair of copper
slugs so there is no feed wire.

Notably, Hitachi lateral mosfets in TO3 pack have aluminium gate and drain
feed wires designed to fuse if the chip ever went short - creating the
unique situation where one Hitachi mosfet in a parallel group could become
short ( drain to source) and yet the power amp still functions.

One then picks out the dud by noting it is much cooler than the rest.



.... Phil

 

[Mark Zacharias]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:lk4o3e$84n$1@dont-email.me...

On 03/05/2014 21:36, Jon Elson wrote:
N_Cook wrote:



Would "suicide diode" be a valid term for searching within a supplier
site?. I've come across guaranteed VTS/diode failure to short and never
open, before , but not able to nail it down. Would you know of any
VTS/diode type number that is definitely made for this purpose?
No, that's my own description. Digi-Key part
SA5.0ALFCT-ND is a representative part, although not the one
I've seen in a particular power supply. (I can't find the
part number of that unit right now.)

Jon


I still cannot find specifically stated , designed to fail short circuit
in any associated datasheet for that TVS. Of course any device might fail
short or even frequently fail short but I've still never found any TVS
designed and stated as such to fail short for safety purposes, ie as you
succinctly term such a theoretical device , a suicide device

Panasonic vcr's from the '90s had ordinary 18v 1-watt zeners across the
output of the 15 volt line. When the supply lost regulation, usually due to
bad caps, the zener would short quite reliably. This was supposed to blow
the fuse but generally took out the switcher transistor as well. Sony's were
better designed - the zener would short, and the switcher was so far out of
it's resonant range it would simply stop running with no other damage.

Mark Z.

 

[N_Cook]

On 04/05/2014 11:52, Mark Zacharias wrote:

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:lk4o3e$84n$1@dont-email.me...
On 03/05/2014 21:36, Jon Elson wrote:
N_Cook wrote:



Would "suicide diode" be a valid term for searching within a supplier
site?. I've come across guaranteed VTS/diode failure to short and never
open, before , but not able to nail it down. Would you know of any
VTS/diode type number that is definitely made for this purpose?
No, that's my own description. Digi-Key part
SA5.0ALFCT-ND is a representative part, although not the one
I've seen in a particular power supply. (I can't find the
part number of that unit right now.)

Jon


I still cannot find specifically stated , designed to fail short
circuit in any associated datasheet for that TVS. Of course any device
might fail short or even frequently fail short but I've still never
found any TVS designed and stated as such to fail short for safety
purposes, ie as you succinctly term such a theoretical device , a
suicide device


Panasonic vcr's from the '90s had ordinary 18v 1-watt zeners across the
output of the 15 volt line. When the supply lost regulation, usually due
to bad caps, the zener would short quite reliably. This was supposed to
blow the fuse but generally took out the switcher transistor as well.
Sony's were better designed - the zener would short, and the switcher
was so far out of it's resonant range it would simply stop running with
no other damage.

Mark Z.

Yes, often such a device will fail short and even anecdotally a lot of
recorded times. But can a designer go to some supplier and get a TVS or
similar that is stated in their datasheet for that device, that it will
fail short circuit with 99.99 percent guarantee or whatever of overload
tests. Then the designer ,allowing for such peak current in pcb traces
etc will know that his appropriately rated fuse elsewhere will go open
circuit?