art wrote:
Yesterday I came across an example where thinking went astray.
My Runco three large CRT projector failed and I traced it to the first
power
supply of all things. There were four square power resisters, two in
series
but what hit me in the head was that the draftsman had put these
resisters in a tight touching square Now you must know that you
add a fudge factor to the power level but you never cancel it by
removing circulation. They didn't have the apearance of damage
but I took them out anyway. True enough two in parallel had blown
and the engineer probably asked for them to be in parallel to provide
the required surface area. I replaced them with tubular hollow wre
wounds
with separation. To many it is only obvious after the fact or shall I
call
them monday morning quarter backs.
I will see the superbowl in my home theatre with a grin on my face
Art


How many hours did you have on this projector at failure? Part of
engineering a design is lifetime expectancy, judging by the projectors
I've seen over the past few years a three CRT projector has exceeded
it's expected lifetime.

"gwatts" wrote in message
...
art wrote:
Yesterday I came across an example where thinking went astray.
My Runco three large CRT projector failed and I traced it to the first
power
supply of all things. There were four square power resisters, two in
series
but what hit me in the head was that the draftsman had put these
resisters in a tight touching square Now you must know that you
add a fudge factor to the power level but you never cancel it by
removing circulation. They didn't have the apearance of damage
but I took them out anyway. True enough two in parallel had blown
and the engineer probably asked for them to be in parallel to provide
the required surface area. I replaced them with tubular hollow wre
wounds
with separation. To many it is only obvious after the fact or shall I
call
them monday morning quarter backs.
I will see the superbowl in my home theatre with a grin on my face Art


How many hours did you have on this projector at failure? Part of
engineering a design is lifetime expectancy, judging by the projectors
I've seen over the past few years a three CRT projector has exceeded it's
expected lifetime.

Yes these are begining to show up in Goodwill stores.

I agree, my 8 inch CRTs have very little hours on them tho I am always
looking for spare tubes. I mentioned it to Curt who fixes them and he
stated it is not the first time he has seen power resisters blow in the
supply.
Manufacturers don't want to add a lot of fans because of the noise.
Similar things happen with the Hitachi rear projection t.v.s maybe
that's why so many are failing. The idea of using two power resisters
in parallel instead of just one of a lower value is purely to take
advantage of the increased surface area, in this case the problem
excabated because the resistors were of the square form so the
draftsman probably placed the four in a tight touching square for
neatness which retarded circulation.i The hollow ohmites that I put in
should solve that oversight. The 8 inch crt forms were made by an
unknown company in Japan for Zenith who then supplied them to G.E., nec
and Runco for relabeling so it may well be a one type set thing
..Have a single lamp projector of Runco but liquid spilt on the power
supply and burnt the traces as well. Do you have the schematic? By the
way the 8 inch crt are underdriven which is a huge advantage in terms
of life. The early forms were over driven which forced designers to go
back to the 7 inch forms and below in the case of rear projection to
accomplish better life.
By the way on single lamp incandescent projector forms I replace the
inside bulb when they fail and use a wire clip to hold it in, much
cheaper than paying a few hundred dollars to replace. I would expect
that the new rear projection lights on the new tvs would benefit from
the same treatment.. I do have a lot of fun playing around with things
to retard the oncomming old age.
Art

gwatts wrote:
art wrote:
Yesterday I came across an example where thinking went astray.
My Runco three large CRT projector failed and I traced it to the first
power
supply of all things. There were four square power resisters, two in
series
but what hit me in the head was that the draftsman had put these
resisters in a tight touching square Now you must know that you
add a fudge factor to the power level but you never cancel it by
removing circulation. They didn't have the apearance of damage
but I took them out anyway. True enough two in parallel had blown
and the engineer probably asked for them to be in parallel to provide
the required surface area. I replaced them with tubular hollow wre
wounds
with separation. To many it is only obvious after the fact or shall I
call
them monday morning quarter backs.
I will see the superbowl in my home theatre with a grin on my face
Art


How many hours did you have on this projector at failure? Part of
engineering a design is lifetime expectancy, judging by the projectors
I've seen over the past few years a three CRT projector has exceeded
it's expected lifetime.

"art" wrote in message
ups.com...
I agree, my 8 inch CRTs have very little hours on them tho I am always
looking for spare tubes. I mentioned it to Curt who fixes them and he
stated it is not the first time he has seen power resisters blow in the
supply.
Manufacturers don't want to add a lot of fans because of the noise.
Similar things happen with the Hitachi rear projection t.v.s maybe
that's why so many are failing. The idea of using two power resisters
in parallel instead of just one of a lower value is purely to take
advantage of the increased surface area, in this case the problem
excabated because the resistors were of the square form so the
draftsman probably placed the four in a tight touching square for
neatness which retarded circulation.i The hollow ohmites that I put in
should solve that oversight. The 8 inch crt forms were made by an
unknown company in Japan for Zenith who then supplied them to G.E., nec
and Runco for relabeling so it may well be a one type set thing
.Have a single lamp projector of Runco but liquid spilt on the power
supply and burnt the traces as well. Do you have the schematic? By the
way the 8 inch crt are underdriven which is a huge advantage in terms
of life. The early forms were over driven which forced designers to go
back to the 7 inch forms and below in the case of rear projection to
accomplish better life.
By the way on single lamp incandescent projector forms I replace the
inside bulb when they fail and use a wire clip to hold it in, much
cheaper than paying a few hundred dollars to replace. I would expect
that the new rear projection lights on the new tvs would benefit from
the same treatment.. I do have a lot of fun playing around with things
to retard the oncomming old age.
Art

gwatts wrote:
art wrote:
Yesterday I came across an example where thinking went astray.
My Runco three large CRT projector failed and I traced it to the first
power
supply of all things. There were four square power resisters, two in
series
but what hit me in the head was that the draftsman had put these
resisters in a tight touching square Now you must know that you
add a fudge factor to the power level but you never cancel it by
removing circulation. They didn't have the apearance of damage
but I took them out anyway. True enough two in parallel had blown
and the engineer probably asked for them to be in parallel to provide
the required surface area. I replaced them with tubular hollow wre
wounds
with separation. To many it is only obvious after the fact or shall I
call
them monday morning quarter backs.
I will see the superbowl in my home theatre with a grin on my face
Art


How many hours did you have on this projector at failure? Part of
engineering a design is lifetime expectancy, judging by the projectors
I've seen over the past few years a three CRT projector has exceeded
it's expected lifetime.


Doubt if it was a fault in engineering. If the engineers had their way it
would probably be a dale heatsinked to the chassis.Often one engineering
team designs it and another goes through to find out how they can cut
corners.

On 23 Jan, 14:49, "Jimmie D" wrote:
"art" wrote in oglegroups.com...





I agree, my 8 inch CRTs have very little hours on them tho I am always
looking for spare tubes. I mentioned it to Curt who fixes them and he
stated it is not the first time he has seen power resisters blow in the
supply.
Manufacturers don't want to add a lot of fans because of the noise.
Similar things happen with the Hitachi rear projection t.v.s maybe
that's why so many are failing. The idea of using two power resisters
in parallel instead of just one of a lower value is purely to take
advantage of the increased surface area, in this case the problem
excabated because the resistors were of the square form so the
draftsman probably placed the four in a tight touching square for
neatness which retarded circulation.i The hollow ohmites that I put in
should solve that oversight. The 8 inch crt forms were made by an
unknown company in Japan for Zenith who then supplied them to G.E., nec
and Runco for relabeling so it may well be a one type set thing
.Have a single lamp projector of Runco but liquid spilt on the power
supply and burnt the traces as well. Do you have the schematic? By the
way the 8 inch crt are underdriven which is a huge advantage in terms
of life. The early forms were over driven which forced designers to go
back to the 7 inch forms and below in the case of rear projection to
accomplish better life.
By the way on single lamp incandescent projector forms I replace the
inside bulb when they fail and use a wire clip to hold it in, much
cheaper than paying a few hundred dollars to replace. I would expect
that the new rear projection lights on the new tvs would benefit from
the same treatment.. I do have a lot of fun playing around with things
to retard the oncomming old age.
Art

gwatts wrote:
art wrote:
Yesterday I came across an example where thinking went astray.
My Runco three large CRT projector failed and I traced it to the first
power
supply of all things. There were four square power resisters, two in
series
but what hit me in the head was that the draftsman had put these
resisters in a tight touching square Now you must know that you
add a fudge factor to the power level but you never cancel it by
removing circulation. They didn't have the apearance of damage
but I took them out anyway. True enough two in parallel had blown
and the engineer probably asked for them to be in parallel to provide
the required surface area. I replaced them with tubular hollow wre
wounds
with separation. To many it is only obvious after the fact or shall I
call
them monday morning quarter backs.
I will see the superbowl in my home theatre with a grin on my face
Art

How many hours did you have on this projector at failure? Part of
engineering a design is lifetime expectancy, judging by the projectors
I've seen over the past few years a three CRT projector has exceeded
it's expected lifetime.Doubt if it was a fault in engineering. If the engineers had their way it
would probably be a dale heatsinked to the chassis.Often one engineering
team designs it and another goes through to find out how they can cut
corners.- Hide quoted text -- Show quoted text -

On 23 Jan, 14:49, "Jimmie D" wrote:
"art" wrote in oglegroups.com...




snipurs did you have on this projector at failure? Part of
engineering a design is lifetime expectancy, judging by the projectors
I've seen over the past few years a three CRT projector has exceeded
it's expected lifetime.Doubt if it was a fault in engineering. If the engineers had their way it
would probably be a dale heatsinked to the chassis.Often one engineering
team designs it and another goes through to find out how they can cut
corners.- Hide quoted text -- Show quoted text -

Jimmy it is rare to use two resisters instead of one because a board
becomes bigger
and introduces cost. When you get to power resisters it is not unusual
to place two
in parallel and accept the cost. In this case a cost improver would
try to make the case
for one single resister instead of four since a Dale with heatsink
would be
comparitively prohibative. The engineers calculation for wattage may
well have
been correct without being side blinded by the fact of some square
form resisters.
Art

"art" wrote in message
oups.com...


On 23 Jan, 14:49, "Jimmie D" wrote:
"art" wrote in
oglegroups.com...




snipurs did you have on this projector at failure? Part of
engineering a design is lifetime expectancy, judging by the projectors
I've seen over the past few years a three CRT projector has exceeded
it's expected lifetime.Doubt if it was a fault in engineering. If the
engineers had their way it
would probably be a dale heatsinked to the chassis.Often one engineering
team designs it and another goes through to find out how they can cut
corners.- Hide quoted text -- Show quoted text -

Jimmy it is rare to use two resisters instead of one because a board
becomes bigger
and introduces cost. When you get to power resisters it is not unusual
to place two
in parallel and accept the cost. In this case a cost improver would
try to make the case
for one single resister instead of four since a Dale with heatsink
would be
comparitively prohibative. The engineers calculation for wattage may
well have
been correct without being side blinded by the fact of some square
form resisters.
Art


Depends on the cost of the resistors. Prices seem to increase somewhat
expotentially with wattage so the two smaller ones may have been cheaper
than one larger. In this case the cost improver would have went for the
multiple resistors.

art wrote:

On 23 Jan, 14:49, "Jimmie D" wrote:
"art" wrote in oglegroups.com...

...Part of
engineering a design is lifetime expectancy...
...Doubt if it was a fault in engineering. If the engineers had their way it
would probably be a dale heatsinked to the chassis.Often one engineering
team designs it and another goes through to find out how they can cut
corners.

Jimmy it is rare to use two resisters instead of one because a board
becomes bigger
and introduces cost.

If they used one resistor in another place or places it's could have
been easier to use multiples in series/parallel where they could rather
than purchase and stock another value at the factory. I worked at a
place where we used 5532 op amps in many audio circuits and in one place
as a flip flop so we wouldn't have to stock a 74xx or 40xx just for that
one use. It was easier on the assemblers to have one bin of chips,
better quantity pricing, no sweating running out of one part kept in
smaller quantity, (insert more bean counter stuff...)

On 23 Jan, 18:14, gwatts wrote:
art wrote:

On 23 Jan, 14:49, "Jimmie D" wrote:
"art" wrote in oglegroups.com...

...Part of
snip where we used 5532 op amps in many audio circuits and in one place
as a flip flop so we wouldn't have to stock a 74xx or 40xx just for that
one use. It was easier on the assemblers to have one bin of chips,
better quantity pricing, no sweating running out of one part kept in
smaller quantity, (insert more bean counter stuff...)

Very interesting if you are refering to power resisters used in a
non switching power supply. In my case I have had no experience
of seeing power supplies with excess resisters or with the use of dale
prescision resisters or resisters mounted on a heat sink which
is fortunate for me otherwise I would never have resolved my
particular problem It would appear that I retired just in time
before engineering studies became out of fashion
Happy trails
Art

art wrote:

On 23 Jan, 18:14, gwatts wrote:

art wrote:


On 23 Jan, 14:49, "Jimmie D" wrote:

"art" wrote in oglegroups.com...

...Part of

snip where we used 5532 op amps in many audio circuits and in one place

as a flip flop so we wouldn't have to stock a 74xx or 40xx just for that
one use. It was easier on the assemblers to have one bin of chips,
better quantity pricing, no sweating running out of one part kept in
smaller quantity, (insert more bean counter stuff...)


Very interesting if you are refering to power resisters used in a
non switching power supply.

Your particular case sounds like they designed for one resistor and
designed very close to the function/failure edge, then rushed to
production only to discover the single resistor was too far over that
edge. Their solution was to quickly change the board design for four in
series-parallel but put them in the same space, since they already had
umpteen thousand resistors ordered or even in stock. It worked in test,
worked for a week or so running continuously... ship it!

... It would appear that I retired just in time
before engineering studies became out of fashion

Engineering studies aren't out of fashion, in fact they're more
intensive, involve a lot more computer modeling and help push the design
closer to the function/failure edge. Not out of fashion but a smaller
piece of the pie, now the design involves a lot more
design-for-manufacture including pick-and-place instead of a human
assembler, all SMT (see previous reason), least component count
possible, limited lifetime so you have to buy a new unit in a few years,
less 'robust design' and more 'economical,' higher profit and lower quality.

Don't blame the engineers, unless they went on to get an MBA after the
EE, ME, etc. I got out of private industry ten years ago for these
reasons, I was tired of design reviews where management pushed the 'you
can cut this out, it won't be so bad' line. Designs aren't for the
benefit of the customer, they are for the benefit of the stockholder and
the board of directors. What was 'The quality goes in before the name
goes on,' is now 'the profit is determined before the unit is produced.'
I'm not saying that profit isn't a good thing, just that it shouldn't
be the overwhelming thing.

73,
W8LNA