"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.