Help identify a component

[Wm James]

I'm trying to repair an optical encoder from a machine and have
trouble identifying a component. It's two leads, surface mount,
rectangular and as tall as it is wide, and about twice as long. The
length is about the same as a 1/2 watt resistor.
It looks like a plastic case, but isn't, breaking it open shows it's
semiconductor material. I suspect it's a diode. One end was burned
enough to make it hard to see any polarity indicator, but it could
have been there. I was barely able to read the numbers on it:

A 475V
P3503

Unfortunately, none of that seems to cross reference with anything
I've found so far witn NEC, ECG, etc., or even googling the numbers.

I would appreciate any assistance. If anyone knows what this device
is, with enough specs to make a substitution, I would appreciate it.
The email addy is valid without the ".nospam.invalid" and or I'll
check beck here.

Thanks

 

[Ross Herbert]

On 16 Apr 2009 17:53:01 -0500, Wm James <wrjames.nospam.invalid@spamreaper.org>
wrote:

:
:I'm trying to repair an optical encoder from a machine and have
:trouble identifying a component. It's two leads, surface mount,
:rectangular and as tall as it is wide, and about twice as long. The
:length is about the same as a 1/2 watt resistor.
: It looks like a plastic case, but isn't, breaking it open shows it's
:semiconductor material. I suspect it's a diode. One end was burned
:enough to make it hard to see any polarity indicator, but it could
:have been there. I was barely able to read the numbers on it:
:
:A 475V
: P3503
:
:Unfortunately, none of that seems to cross reference with anything
:I've found so far witn NEC, ECG, etc., or even googling the numbers.
:
:I would appreciate any assistance. If anyone knows what this device
:is, with enough specs to make a substitution, I would appreciate it.
:The email addy is valid without the ".nospam.invalid" and or I'll
:check beck here.
:
:Thanks

A pic on alt.binaries.schematics.electronic is worth a thousand words.....

 

[legg]

On 16 Apr 2009 17:53:01 -0500, Wm James
<wrjames.nospam.invalid@spamreaper.org> wrote:

I'm trying to repair an optical encoder from a machine and have
trouble identifying a component. It's two leads, surface mount,
rectangular and as tall as it is wide, and about twice as long. The
length is about the same as a 1/2 watt resistor.
It looks like a plastic case, but isn't, breaking it open shows it's
semiconductor material. I suspect it's a diode. One end was burned
enough to make it hard to see any polarity indicator, but it could
have been there. I was barely able to read the numbers on it:

A 475V
P3503

Location in the circuit? Length and width in real units?

Not a plastic case - what material is the case or is there only a
coating.

Colour.

Are there 'leads' formed for smd or are the ends metalized for surface
reflow - shape and extent of either?

Semiconductor material??? Describe it.

Very little of the actual contents of a diode package is actually
semiconductor - a small wafer usually dwarfed by the soldering
interface and metal lead-out. The same is ~ true of polymer ptc's.

Varistors and some thermistors will be a solid crystaline structure
with the consistency of pencil lead-graphite.

The part burnt or solder junction burnt? Burning extends into body or
just on surface?

RL