Jim Adney wrote:

If I'm that tech, how do I correlate that p/n with this cap on the
schematic? Does the schematic have both the value AND the p/n on it?

I understand your point about using the exact replacement, but I don't
see why a part should not have BOTH sets of data. To me, that seems
like it adds a lot of value to the part.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Typically, the schematic will identify the part by "circuit number", say
C143 (and might or might not show the value), and it'll be on page A4B3,
which is the schematic for board B3 in larger assembly A4. In the same
manual, there'll be a parts list for A4B3, where you can find the
description of C143, along with its part number. It would certainly
include the value, type, and probably the tolerance, which are important
to know when troubleshooting. Sometimes it'll tell a little more, if
there's something particularly unusual about the part. But the full
description of that part #20035942 only appears on a document that's
typically many pages long and fully describes its specifications. There
might be 100 different part numbers for 4.7 uF, 10%, 50 volt tantalum
capacitors, each with different specifications for reliability testing,
temperature range, ESR, mechanical lead strength, vibration tolerance,
tada, tada, tada. They are *NOT* interchangeable in the military or
commercial environment. Substitution could result in failure at a
critical time or place with incredibly expensive, disastrous, or fatal
consequences.

When replacing the part, the only thing that's important to the
technician is whether the replacement has the right part number. If it
doesn't, the part doesn't go in, regardless of what its capacitance
value might be.

Yep, stamping the value on the capacitor would undoubtedly add value to
the part for you and me. But again, the military just wasn't thinking of
us when it set up its stock system.

Roy Lewallen, W7EL

In article ,
(Avery Fineman) wrote:

In article , Al
writes:

big snip
Each component, yes even a carbon
composition resistor, had a serial number on it. Why? So it could be
traced back to the lot from it which it had been selected if it failed.


I'm going to challenge the veracity of that claim due to "having been
there, done that," and only seeing that in NASA electronics.

Think ICBM with its ground support system.

Al

--
There's never enough time to do it right the first time.......

In article ,
(Avery Fineman) wrote:

In article , Al
writes:

big snip
Each component, yes even a carbon
composition resistor, had a serial number on it. Why? So it could be
traced back to the lot from it which it had been selected if it failed.


I'm going to challenge the veracity of that claim due to "having been
there, done that," and only seeing that in NASA electronics.

Think ICBM with its ground support system.

Al

--
There's never enough time to do it right the first time.......

In fact, it's becoming much less common to find parts in commercial
equipment with only the OEM user's part number rather than the
manufacturer's PN on them. Partly this is being driven by contract
manufacturing of the boards, but it was a trend even before CM became
so common, in my experience.

Roy's comments about military techs are slightly idealistic, if I
relate things to my personal experience some years ago. My shop
supervisor at a remote site quickly learned to trust my judgement in
finding ways to get things repaired and functioning reliably when
parts simply weren't available. When it comes to a decision between
completing a critical mission using a part that gets you through the
mission, and waiting six months for a part, guess which wins. You can
find info about some of that sort of thing on the NASA web site.
Astronauts don't wait for delivery of XPQ1453762 if their lives (or
even an expensive experiment) can be saved by using something on hand.
Clearly, you'd prefer to use the exact part specified, or a
documented replacement, but there are lots of times when waiting for
that would be very poor judgement. (Darwin award candidates??)

OTOH, do NOT expect modern parts to be fully labeled. Don't expect
0.1% SMT resistors to have anything on them telling you that they are
0.1%. Don't expect 0603 and smaller resistors and capacitors to have
ANY marking, though some do. Don't expect SOT-23 and SC-70 parts to
have anything but a simple 2 or 3 character code on them. Some
(most?) SMT tantalum cap manufacturers don't seem to put a marking on
them that tells you which series they are (std ESR, low ESR, extra-low
ESR, fused, mil-spec...).

And count your blessings that you're dealing with electronic parts,
where labelling with the value is pretty common. That's not the case
with most mechanical parts, for example. Would you expect Honda
pistons to fit any Toyota engines? Have you ever seen ANY springs
labelled with their spring constant, let alone any of their other
parameters? Most aren't even labelled with a part number.

Finally, there IS a reason that schematics don't always have values or
manufacturer's part numbers on them, or even house part numbers, but
only a reference designator. That's because values (and therefore the
part numbers) may well change over time. It's a lot easier and less
error-prone to maintain only one changing document: the material list
used to build the board. Not everyone agrees with that, and in fact I
do prefer to have values and mfgr's part numbers on my schematics.

Cheers,
Tom


Jim Adney wrote in message . ..
On Tue, 09 Mar 2004 19:59:19 -0800 Roy Lewallen
wrote:

Jim Adney wrote:
. . .
So I still don't think it's too much to ask that the most important
data be printed out separately.

Obviously, I don't tend to think like the military....

While you've got a legitimate point, you've got to realize the function
of the part number. If you're a technician servicing a piece of military
gear, you replace a 20035942 *ONLY* with a 20035942, not *ANY* other
capacitor, regardless of its value. To order a replacement, you put in a
requisition for a 20035942. Now, it's vital to you that the capacitors
in the stock bin or coming in from the supply system have 20035942
printed on them, but it's not important that the value is. The
technician can find the value in the parts list in the manual and likely
on the schematic.

If I'm that tech, how do I correlate that p/n with this cap on the
schematic? Does the schematic have both the value AND the p/n on it?

I understand your point about using the exact replacement, but I don't
see why a part should not have BOTH sets of data. To me, that seems
like it adds a lot of value to the part.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

In fact, it's becoming much less common to find parts in commercial
equipment with only the OEM user's part number rather than the
manufacturer's PN on them. Partly this is being driven by contract
manufacturing of the boards, but it was a trend even before CM became
so common, in my experience.

Roy's comments about military techs are slightly idealistic, if I
relate things to my personal experience some years ago. My shop
supervisor at a remote site quickly learned to trust my judgement in
finding ways to get things repaired and functioning reliably when
parts simply weren't available. When it comes to a decision between
completing a critical mission using a part that gets you through the
mission, and waiting six months for a part, guess which wins. You can
find info about some of that sort of thing on the NASA web site.
Astronauts don't wait for delivery of XPQ1453762 if their lives (or
even an expensive experiment) can be saved by using something on hand.
Clearly, you'd prefer to use the exact part specified, or a
documented replacement, but there are lots of times when waiting for
that would be very poor judgement. (Darwin award candidates??)

OTOH, do NOT expect modern parts to be fully labeled. Don't expect
0.1% SMT resistors to have anything on them telling you that they are
0.1%. Don't expect 0603 and smaller resistors and capacitors to have
ANY marking, though some do. Don't expect SOT-23 and SC-70 parts to
have anything but a simple 2 or 3 character code on them. Some
(most?) SMT tantalum cap manufacturers don't seem to put a marking on
them that tells you which series they are (std ESR, low ESR, extra-low
ESR, fused, mil-spec...).

And count your blessings that you're dealing with electronic parts,
where labelling with the value is pretty common. That's not the case
with most mechanical parts, for example. Would you expect Honda
pistons to fit any Toyota engines? Have you ever seen ANY springs
labelled with their spring constant, let alone any of their other
parameters? Most aren't even labelled with a part number.

Finally, there IS a reason that schematics don't always have values or
manufacturer's part numbers on them, or even house part numbers, but
only a reference designator. That's because values (and therefore the
part numbers) may well change over time. It's a lot easier and less
error-prone to maintain only one changing document: the material list
used to build the board. Not everyone agrees with that, and in fact I
do prefer to have values and mfgr's part numbers on my schematics.

Cheers,
Tom


Jim Adney wrote in message . ..
On Tue, 09 Mar 2004 19:59:19 -0800 Roy Lewallen
wrote:

Jim Adney wrote:
. . .
So I still don't think it's too much to ask that the most important
data be printed out separately.

Obviously, I don't tend to think like the military....

While you've got a legitimate point, you've got to realize the function
of the part number. If you're a technician servicing a piece of military
gear, you replace a 20035942 *ONLY* with a 20035942, not *ANY* other
capacitor, regardless of its value. To order a replacement, you put in a
requisition for a 20035942. Now, it's vital to you that the capacitors
in the stock bin or coming in from the supply system have 20035942
printed on them, but it's not important that the value is. The
technician can find the value in the parts list in the manual and likely
on the schematic.

If I'm that tech, how do I correlate that p/n with this cap on the
schematic? Does the schematic have both the value AND the p/n on it?

I understand your point about using the exact replacement, but I don't
see why a part should not have BOTH sets of data. To me, that seems
like it adds a lot of value to the part.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

On Thu, 11 Mar 2004 00:43:21 -0800 Roy Lewallen
wrote:

Yep, stamping the value on the capacitor would undoubtedly add value to
the part for you and me. But again, the military just wasn't thinking of
us when it set up its stock system.

I was thinking of the value it would have to the tech, in helping him
to make sure that the part he was looking at on the schematic and the
part that he was replacing in the circuit were the same item.

If he has to trace the item from the schematic (C437) to the parts
list (M390009/xxxx) to the chassis (M390009/xxxx) that's an extra step
where time is wasted and a mistake could be made. Both would be
counterproductive, in any environment.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

On Thu, 11 Mar 2004 00:43:21 -0800 Roy Lewallen
wrote:

Yep, stamping the value on the capacitor would undoubtedly add value to
the part for you and me. But again, the military just wasn't thinking of
us when it set up its stock system.

I was thinking of the value it would have to the tech, in helping him
to make sure that the part he was looking at on the schematic and the
part that he was replacing in the circuit were the same item.

If he has to trace the item from the schematic (C437) to the parts
list (M390009/xxxx) to the chassis (M390009/xxxx) that's an extra step
where time is wasted and a mistake could be made. Both would be
counterproductive, in any environment.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------