In article om,
"Henry Kolesnik" wrote:

I was a GCA radar tech in the RCAF in the 1960s and in one of the excercises
(war games) we had to find and fix a fault so the incoming aircraft
wouldn't crash, it was zero visibility . Sometimes it was as easy as a bad
or loose tube, but some seargents had subchassis with cold solder joints,
shorted black beauty capacitors or fried resistors. Time was critcal as the
weather was closing fast and the aircraft was low on fuel. Sometimes the
excercise left us without many parts, partially functional test equpt, and
only partial manuals. To better simulate battle conditions, one end of the
hut could be on fire and CO2 smoke to hinder visibilty! A shorted .01 uF
400VDC black beauty was easliy replaced with a .01 uF 600VDC or .02 a fried
22K 1/2 watt with a 22K 2 watt or something close. Color codes were quite
useful in many cases. The objective was to save the aircraft using limited
resources. Today I don't think we see component level repair in the field
but in battle anything may be necessary for survival. I'd much rather have
something with component values rather than a bunch of codes that required
decifering. I still contend this is a result of "military intelligence."
And the codes make it tough on us hobbyists but we not under a critical time
crunch and with the Internet it's usually a piece of cake.

In the sixties that was possible. But now you can't really fly by the
seat of your pants. Repair is by replacing LRUs (Least Replaceable
Units). Even if the LRU makes it back to the depot for failure
confirmation, it may not be repairable. 6, 8 or 12 layer PCBs cannot be
readily repaired. And would you trust one that was repaired if it did
not go through a burn-in cycle afterward? Would you depend on a
fail-safe circuit to prevent a nuclear launch if it had a component
replaced in it that was "close enough?" Maybe in your cars brake system,
but not on my missile!

Al

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

"Al" wrote in message
...
In article om,
"Henry Kolesnik" wrote:

I was a GCA radar tech in the RCAF in the 1960s and in one of the
excercises
(war games) we had to find and fix a fault so the incoming aircraft
wouldn't crash, it was zero visibility . Sometimes it was as easy as a
bad
or loose tube, but some seargents had subchassis with cold solder
joints,
shorted black beauty capacitors or fried resistors. Time was critcal as
the
weather was closing fast and the aircraft was low on fuel. Sometimes
the
excercise left us without many parts, partially functional test equpt,
and
only partial manuals. To better simulate battle conditions, one end of
the
hut could be on fire and CO2 smoke to hinder visibilty! A shorted .01
uF
400VDC black beauty was easliy replaced with a .01 uF 600VDC or .02 a
fried
22K 1/2 watt with a 22K 2 watt or something close. Color codes were
quite
useful in many cases. The objective was to save the aircraft using
limited
resources. Today I don't think we see component level repair in the
field
but in battle anything may be necessary for survival. I'd much rather
have
something with component values rather than a bunch of codes that
required
decifering. I still contend this is a result of "military
intelligence."
And the codes make it tough on us hobbyists but we not under a critical
time
crunch and with the Internet it's usually a piece of cake.

In the sixties that was possible. But now you can't really fly by the
seat of your pants. Repair is by replacing LRUs (Least Replaceable
Units). Even if the LRU makes it back to the depot for failure
confirmation, it may not be repairable. 6, 8 or 12 layer PCBs cannot be
readily repaired. And would you trust one that was repaired if it did
not go through a burn-in cycle afterward? Would you depend on a
fail-safe circuit to prevent a nuclear launch if it had a component
replaced in it that was "close enough?" Maybe in your cars brake system,
but not on my missile!
True, in the 'close enough' stakes, but it is well worth reflecting that 90%
of simple systems use a relatively small 'subset' of parts from the avilable
world pool. An engineer, with one each of the IC's for a range of boards,
and a few dozen resistors and capacitors, can potentially repair most faults
on such boards 'on site', especially if the board is designed with this in
mind (possibly with some form of self diagnostics for many parts). However
if the same units are built with SM parts in quantity, using custom IC's,
the solution becomes to carry a complete replacement board. Doing this for a
few dozen products is often not practical. The problem here is that the
custom IC/SM solution is cheaper once production reaches a reasonable level,
but is not the best solution where the units are going to be a long way from
'spares'.
I designed a range of units used on sites across many third-world countries,
and it became necessary to deliberately design the units with both
redundancy, and repairability in mind. Given that the service engineer may
have to travel 1000miles to get to a unit, having it so that repair is
likely to be possible, was a vital design criterion. The parts list was
deliberately 'shrunk', retaining as far as was practical a limited range of
parts used in all. Unfortunately the relative costs of truly 'mass'
production, combined with robot construction/assembly, make such designs a
'dying art'...

Best Wishes

"Al" wrote in message
...
In article om,
"Henry Kolesnik" wrote:

I was a GCA radar tech in the RCAF in the 1960s and in one of the
excercises
(war games) we had to find and fix a fault so the incoming aircraft
wouldn't crash, it was zero visibility . Sometimes it was as easy as a
bad
or loose tube, but some seargents had subchassis with cold solder
joints,
shorted black beauty capacitors or fried resistors. Time was critcal as
the
weather was closing fast and the aircraft was low on fuel. Sometimes
the
excercise left us without many parts, partially functional test equpt,
and
only partial manuals. To better simulate battle conditions, one end of
the
hut could be on fire and CO2 smoke to hinder visibilty! A shorted .01
uF
400VDC black beauty was easliy replaced with a .01 uF 600VDC or .02 a
fried
22K 1/2 watt with a 22K 2 watt or something close. Color codes were
quite
useful in many cases. The objective was to save the aircraft using
limited
resources. Today I don't think we see component level repair in the
field
but in battle anything may be necessary for survival. I'd much rather
have
something with component values rather than a bunch of codes that
required
decifering. I still contend this is a result of "military
intelligence."
And the codes make it tough on us hobbyists but we not under a critical
time
crunch and with the Internet it's usually a piece of cake.

In the sixties that was possible. But now you can't really fly by the
seat of your pants. Repair is by replacing LRUs (Least Replaceable
Units). Even if the LRU makes it back to the depot for failure
confirmation, it may not be repairable. 6, 8 or 12 layer PCBs cannot be
readily repaired. And would you trust one that was repaired if it did
not go through a burn-in cycle afterward? Would you depend on a
fail-safe circuit to prevent a nuclear launch if it had a component
replaced in it that was "close enough?" Maybe in your cars brake system,
but not on my missile!
True, in the 'close enough' stakes, but it is well worth reflecting that 90%
of simple systems use a relatively small 'subset' of parts from the avilable
world pool. An engineer, with one each of the IC's for a range of boards,
and a few dozen resistors and capacitors, can potentially repair most faults
on such boards 'on site', especially if the board is designed with this in
mind (possibly with some form of self diagnostics for many parts). However
if the same units are built with SM parts in quantity, using custom IC's,
the solution becomes to carry a complete replacement board. Doing this for a
few dozen products is often not practical. The problem here is that the
custom IC/SM solution is cheaper once production reaches a reasonable level,
but is not the best solution where the units are going to be a long way from
'spares'.
I designed a range of units used on sites across many third-world countries,
and it became necessary to deliberately design the units with both
redundancy, and repairability in mind. Given that the service engineer may
have to travel 1000miles to get to a unit, having it so that repair is
likely to be possible, was a vital design criterion. The parts list was
deliberately 'shrunk', retaining as far as was practical a limited range of
parts used in all. Unfortunately the relative costs of truly 'mass'
production, combined with robot construction/assembly, make such designs a
'dying art'...

Best Wishes

In article 2HI3c.3458$re1.1290@newsfe1-win,
"Roger Hamlett" wrote:

"Al" wrote in message
...
In article om,
"Henry Kolesnik" wrote:

I was a GCA radar tech in the RCAF in the 1960s and in one of the
excercises
(war games) we had to find and fix a fault so the incoming aircraft
wouldn't crash, it was zero visibility . Sometimes it was as easy as a
bad
or loose tube, but some seargents had subchassis with cold solder
joints,
shorted black beauty capacitors or fried resistors. Time was critcal as
the
weather was closing fast and the aircraft was low on fuel. Sometimes
the
excercise left us without many parts, partially functional test equpt,
and
only partial manuals. To better simulate battle conditions, one end of
the
hut could be on fire and CO2 smoke to hinder visibilty! A shorted .01
uF
400VDC black beauty was easliy replaced with a .01 uF 600VDC or .02 a
fried
22K 1/2 watt with a 22K 2 watt or something close. Color codes were
quite
useful in many cases. The objective was to save the aircraft using
limited
resources. Today I don't think we see component level repair in the
field
but in battle anything may be necessary for survival. I'd much rather
have
something with component values rather than a bunch of codes that
required
decifering. I still contend this is a result of "military
intelligence."
And the codes make it tough on us hobbyists but we not under a critical
time
crunch and with the Internet it's usually a piece of cake.

In the sixties that was possible. But now you can't really fly by the
seat of your pants. Repair is by replacing LRUs (Least Replaceable
Units). Even if the LRU makes it back to the depot for failure
confirmation, it may not be repairable. 6, 8 or 12 layer PCBs cannot be
readily repaired. And would you trust one that was repaired if it did
not go through a burn-in cycle afterward? Would you depend on a
fail-safe circuit to prevent a nuclear launch if it had a component
replaced in it that was "close enough?" Maybe in your cars brake system,
but not on my missile!
True, in the 'close enough' stakes, but it is well worth reflecting that 90%
of simple systems use a relatively small 'subset' of parts from the avilable
world pool. An engineer, with one each of the IC's for a range of boards,
and a few dozen resistors and capacitors, can potentially repair most faults
on such boards 'on site', especially if the board is designed with this in
mind (possibly with some form of self diagnostics for many parts). However
if the same units are built with SM parts in quantity, using custom IC's,
the solution becomes to carry a complete replacement board. Doing this for a
few dozen products is often not practical. The problem here is that the
custom IC/SM solution is cheaper once production reaches a reasonable level,
but is not the best solution where the units are going to be a long way from
'spares'.
I designed a range of units used on sites across many third-world countries,
and it became necessary to deliberately design the units with both
redundancy, and repairability in mind. Given that the service engineer may
have to travel 1000miles to get to a unit, having it so that repair is
likely to be possible, was a vital design criterion. The parts list was
deliberately 'shrunk', retaining as far as was practical a limited range of
parts used in all. Unfortunately the relative costs of truly 'mass'
production, combined with robot construction/assembly, make such designs a
'dying art'...

Best Wishes

If your design criterion is that the equipment be field repairable with
readily available parts, then so be it. I have no argument with that!
But in the high-reliability military electronics world in which I worked
in the late 60's, that was not possible. Would you believe that one
printed circuit card, 4 in by 6 in, was needed just to implement 4
flip-flops using descrete components. 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.
And boy, did those components have to be reliable! So that's why the
military specifications with their "strange" component markings were
invented. Expensive? Lordy, lordy! I was very shocked one day when I
requisitioned a capacitor from stock to compare to a rejected one. The
price for that unit, a precision paper mylar cap. was $100 - in 1970's
dollars! I almost fell out of my chair! And now you can buy stuff like
that, surplus, for just pennies on the dollar...and with their strange
markings.

I have a bag full of CSR13G825KR's! Anybody need one?

Al

Al

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

In article 2HI3c.3458$re1.1290@newsfe1-win,
"Roger Hamlett" wrote:

"Al" wrote in message
...
In article om,
"Henry Kolesnik" wrote:

I was a GCA radar tech in the RCAF in the 1960s and in one of the
excercises
(war games) we had to find and fix a fault so the incoming aircraft
wouldn't crash, it was zero visibility . Sometimes it was as easy as a
bad
or loose tube, but some seargents had subchassis with cold solder
joints,
shorted black beauty capacitors or fried resistors. Time was critcal as
the
weather was closing fast and the aircraft was low on fuel. Sometimes
the
excercise left us without many parts, partially functional test equpt,
and
only partial manuals. To better simulate battle conditions, one end of
the
hut could be on fire and CO2 smoke to hinder visibilty! A shorted .01
uF
400VDC black beauty was easliy replaced with a .01 uF 600VDC or .02 a
fried
22K 1/2 watt with a 22K 2 watt or something close. Color codes were
quite
useful in many cases. The objective was to save the aircraft using
limited
resources. Today I don't think we see component level repair in the
field
but in battle anything may be necessary for survival. I'd much rather
have
something with component values rather than a bunch of codes that
required
decifering. I still contend this is a result of "military
intelligence."
And the codes make it tough on us hobbyists but we not under a critical
time
crunch and with the Internet it's usually a piece of cake.

In the sixties that was possible. But now you can't really fly by the
seat of your pants. Repair is by replacing LRUs (Least Replaceable
Units). Even if the LRU makes it back to the depot for failure
confirmation, it may not be repairable. 6, 8 or 12 layer PCBs cannot be
readily repaired. And would you trust one that was repaired if it did
not go through a burn-in cycle afterward? Would you depend on a
fail-safe circuit to prevent a nuclear launch if it had a component
replaced in it that was "close enough?" Maybe in your cars brake system,
but not on my missile!
True, in the 'close enough' stakes, but it is well worth reflecting that 90%
of simple systems use a relatively small 'subset' of parts from the avilable
world pool. An engineer, with one each of the IC's for a range of boards,
and a few dozen resistors and capacitors, can potentially repair most faults
on such boards 'on site', especially if the board is designed with this in
mind (possibly with some form of self diagnostics for many parts). However
if the same units are built with SM parts in quantity, using custom IC's,
the solution becomes to carry a complete replacement board. Doing this for a
few dozen products is often not practical. The problem here is that the
custom IC/SM solution is cheaper once production reaches a reasonable level,
but is not the best solution where the units are going to be a long way from
'spares'.
I designed a range of units used on sites across many third-world countries,
and it became necessary to deliberately design the units with both
redundancy, and repairability in mind. Given that the service engineer may
have to travel 1000miles to get to a unit, having it so that repair is
likely to be possible, was a vital design criterion. The parts list was
deliberately 'shrunk', retaining as far as was practical a limited range of
parts used in all. Unfortunately the relative costs of truly 'mass'
production, combined with robot construction/assembly, make such designs a
'dying art'...

Best Wishes

If your design criterion is that the equipment be field repairable with
readily available parts, then so be it. I have no argument with that!
But in the high-reliability military electronics world in which I worked
in the late 60's, that was not possible. Would you believe that one
printed circuit card, 4 in by 6 in, was needed just to implement 4
flip-flops using descrete components. 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.
And boy, did those components have to be reliable! So that's why the
military specifications with their "strange" component markings were
invented. Expensive? Lordy, lordy! I was very shocked one day when I
requisitioned a capacitor from stock to compare to a rejected one. The
price for that unit, a precision paper mylar cap. was $100 - in 1970's
dollars! I almost fell out of my chair! And now you can buy stuff like
that, surplus, for just pennies on the dollar...and with their strange
markings.

I have a bag full of CSR13G825KR's! Anybody need one?

Al

Al

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

In article , Al
writes:

If your design criterion is that the equipment be field repairable with
readily available parts, then so be it. I have no argument with that!
But in the high-reliability military electronics world in which I worked
in the late 60's, that was not possible.

In the late 1960s I was working in both commercial, space, and
military electronics. Only the space electronics (unmanned space-
craft done at Electro-Optical Systems, EOS, in Pasadena, CA, a
Xerox division) was there traceability to that extent, plus the "JAN
TX" or tested-extra solid-state components. That was with reasonable
logic since no company would pay per diem for in-the-field space-
craft repairpersons... :-)

I might note that the little labels used to mark the components were
of a selected brand...to avoid outgassing in vacuum of space and
thus coating some other spacecraft instrument or sensor. Some
have called such a practice "braindead procedures by NASA" but
those people are themselves braindead for not thinking through for
operating in a very different environment.

Since that time I've been involved in a lot of other DoD electronics
and have never seen that level of traceability except in certain
prototypes and then used solely for development testing. NASA
man-rating specs - not Mil Specs unless called out for common
types - required screening and traceability for a very good reason
that humans were aboard those spacecraft (STS or "shuttle").
Astronauts shouldn't be required to get down to the PCB level and
unsolder bad components and resolder new ones in microgravity
for one reason. Another reason is that they can't GET to a part
such as the ignitor of an SSME (Space Shuttle Main Engine,
built at Rocketdyne Division of Rockwell International in Canoga
Park, CA, - now a division of Boeing Aircraft). That ignitor was
often called a "spark plug" in-house but was really a redundant
astable multivibrator turned on remotely and a driver for an
external arc gap...the entire "ignition system" in one extremely
clean (had to work in pure oxygen environment) little unit that had
to work just fine in vibration you couldn't possibly imagine.

Much military radio and electronics equipment bears something
resembling screening markings on modules but any research into
that will show they are merely in-house or depot markings for ID
and other things, not traceability. If you see the insides of an
AN/PRC-104 HF transceiver or an AN/PRC-119 VHF FHSS
transceiver, you will see what I'm talking about.

Would you believe that one
printed circuit card, 4 in by 6 in, was needed just to implement 4
flip-flops using descrete components.

That's not at all strange for the late 1960s. Integrated circuits
weren't there to use, and had only begun to be Mil Specced.
Those were new from Texas Instruments and still the old DTL or
Diode-Transistor-Logic.

The IBM 360 and RCA Spectra 70 used discrete-transistor PCBs
in the 1970s. IBM didn't go into TTL ICs in a large way until the
IBM 370 VM and production starting around 1975.

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.
And boy, did those components have to be reliable! So that's why the
military specifications with their "strange" component markings were
invented. Expensive? Lordy, lordy! I was very shocked one day when I
requisitioned a capacitor from stock to compare to a rejected one. The
price for that unit, a precision paper mylar cap. was $100 - in 1970's
dollars! I almost fell out of my chair! And now you can buy stuff like
that, surplus, for just pennies on the dollar...and with their strange
markings.

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

Also, I have yet to see any "surplus" spacecraft, including the
engineering and test models that never flew.

Back in 1974 I and a co-worker were stuck in Galveston, TX, for an
RCA Corporation field test. We visited the Manned Space Flight
Center in nearby Clear Lake and did a walking tour on a Sunday,
unescorted as was the norm on Sundays there. I wanted to show
the friend the Solar Wind Spectrometer instrument built for the
ALSEP (Apollo Lunar Surface Experiment Package) in 1967. I had
handled all of the SWSs when they were built. All of the ALSEP
modules - except the SWS - were arranged around the "left-over"
Landing and Ascent stages in the lobby. I snagged a docent and
asked about the "missing" instrument. She went off and returned,
said "sorry, it is still being used in a lab experiment." Seven years
later and it was still working...after having gone through some tough
environmental testing on earth.

NASA manned or unmanned electronics is subject to the maximum
in traceability. Military fielded electronics has had traceability
limited to specific lots identified through records and specified
percentage sampling tests on those lots. Samples may be tested
to destruction depending on the Mil Specification. All that TESTING
effort is what drives the parts cost up AND having to package spares
in extra-special protection envelopes and containers since they may
be sitting waiting in some terrible environment somewhere in the
world. World War 2 production and logistics taught the U.S. military
much about needing spares and how to ship and store everything.
USA has always been darn good about logistics and supply and
has been successful at it.

To those folks who want to sneer at "military intelligence," fine.
Nobody is forcing them to like military electronics or the military.
Let them build things for room-temperature environments using
surplus CB radio parts or those from TV sets. However, when
those also sneer at little things like nomenclature about high quality
stuff available surplus at cut rate, it does warrant a strong response.

Roy Lewallen had the succinct response. :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , Al
writes:

If your design criterion is that the equipment be field repairable with
readily available parts, then so be it. I have no argument with that!
But in the high-reliability military electronics world in which I worked
in the late 60's, that was not possible.

In the late 1960s I was working in both commercial, space, and
military electronics. Only the space electronics (unmanned space-
craft done at Electro-Optical Systems, EOS, in Pasadena, CA, a
Xerox division) was there traceability to that extent, plus the "JAN
TX" or tested-extra solid-state components. That was with reasonable
logic since no company would pay per diem for in-the-field space-
craft repairpersons... :-)

I might note that the little labels used to mark the components were
of a selected brand...to avoid outgassing in vacuum of space and
thus coating some other spacecraft instrument or sensor. Some
have called such a practice "braindead procedures by NASA" but
those people are themselves braindead for not thinking through for
operating in a very different environment.

Since that time I've been involved in a lot of other DoD electronics
and have never seen that level of traceability except in certain
prototypes and then used solely for development testing. NASA
man-rating specs - not Mil Specs unless called out for common
types - required screening and traceability for a very good reason
that humans were aboard those spacecraft (STS or "shuttle").
Astronauts shouldn't be required to get down to the PCB level and
unsolder bad components and resolder new ones in microgravity
for one reason. Another reason is that they can't GET to a part
such as the ignitor of an SSME (Space Shuttle Main Engine,
built at Rocketdyne Division of Rockwell International in Canoga
Park, CA, - now a division of Boeing Aircraft). That ignitor was
often called a "spark plug" in-house but was really a redundant
astable multivibrator turned on remotely and a driver for an
external arc gap...the entire "ignition system" in one extremely
clean (had to work in pure oxygen environment) little unit that had
to work just fine in vibration you couldn't possibly imagine.

Much military radio and electronics equipment bears something
resembling screening markings on modules but any research into
that will show they are merely in-house or depot markings for ID
and other things, not traceability. If you see the insides of an
AN/PRC-104 HF transceiver or an AN/PRC-119 VHF FHSS
transceiver, you will see what I'm talking about.

Would you believe that one
printed circuit card, 4 in by 6 in, was needed just to implement 4
flip-flops using descrete components.

That's not at all strange for the late 1960s. Integrated circuits
weren't there to use, and had only begun to be Mil Specced.
Those were new from Texas Instruments and still the old DTL or
Diode-Transistor-Logic.

The IBM 360 and RCA Spectra 70 used discrete-transistor PCBs
in the 1970s. IBM didn't go into TTL ICs in a large way until the
IBM 370 VM and production starting around 1975.

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.
And boy, did those components have to be reliable! So that's why the
military specifications with their "strange" component markings were
invented. Expensive? Lordy, lordy! I was very shocked one day when I
requisitioned a capacitor from stock to compare to a rejected one. The
price for that unit, a precision paper mylar cap. was $100 - in 1970's
dollars! I almost fell out of my chair! And now you can buy stuff like
that, surplus, for just pennies on the dollar...and with their strange
markings.

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

Also, I have yet to see any "surplus" spacecraft, including the
engineering and test models that never flew.

Back in 1974 I and a co-worker were stuck in Galveston, TX, for an
RCA Corporation field test. We visited the Manned Space Flight
Center in nearby Clear Lake and did a walking tour on a Sunday,
unescorted as was the norm on Sundays there. I wanted to show
the friend the Solar Wind Spectrometer instrument built for the
ALSEP (Apollo Lunar Surface Experiment Package) in 1967. I had
handled all of the SWSs when they were built. All of the ALSEP
modules - except the SWS - were arranged around the "left-over"
Landing and Ascent stages in the lobby. I snagged a docent and
asked about the "missing" instrument. She went off and returned,
said "sorry, it is still being used in a lab experiment." Seven years
later and it was still working...after having gone through some tough
environmental testing on earth.

NASA manned or unmanned electronics is subject to the maximum
in traceability. Military fielded electronics has had traceability
limited to specific lots identified through records and specified
percentage sampling tests on those lots. Samples may be tested
to destruction depending on the Mil Specification. All that TESTING
effort is what drives the parts cost up AND having to package spares
in extra-special protection envelopes and containers since they may
be sitting waiting in some terrible environment somewhere in the
world. World War 2 production and logistics taught the U.S. military
much about needing spares and how to ship and store everything.
USA has always been darn good about logistics and supply and
has been successful at it.

To those folks who want to sneer at "military intelligence," fine.
Nobody is forcing them to like military electronics or the military.
Let them build things for room-temperature environments using
surplus CB radio parts or those from TV sets. However, when
those also sneer at little things like nomenclature about high quality
stuff available surplus at cut rate, it does warrant a strong response.

Roy Lewallen had the succinct response. :-)

Len Anderson
retired (from regular hours) electronic engineer person

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 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
-----------------------------------------------

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