tick - tick - tick
The horizontal output FET was dead shorted.
The original is a P9NC60, a TO-220 case deal, which has scant info on the
web.
The best resolution datasheet I found is 90% illegible:
http://home.comcast.net/~tomdempster/temp/P9NC60.gif

No matter:
Schematic actually indicates Q504 is a more familiar 2SK2761:
http://home.comcast.net/~tomdempster/temp/m992dell.pdf
Side note however: There are some slight differences between the M992 I have
and that shown in the schematic; but the horizontal output section seems to
be indentical.
I got a 2SK2761 and put it in.
Power up.
The 2nd anode HV came up OK, but not for long: I heard normal dust crackling
sounds for about 3 seconds, then no HV, no raster, and the SMPS goes into
ticking again.
Yes the new 2SK2761 is now dead shorted.

The P9NC60 is a metal tab style TO-220, and it had one of those grey
flexible style insulators at the heat sink.
The 2SK2761 is a plastic case / tab TO-220, so I used the usual thin layer
of heat sink compound and left out the insulator.

The P9NC60 data sheet [ P9NC60.gif ] isn't legible, and I don't know how to
evaluate the schematic to determine requirements for a good substitute for
the P9NC60.
Availability of an actual P9NC60 looks pretty poor (unless I want to order
1000 of them)
Are there cases where excessive load downstream results in failure of the
horizontal output transistor? A shorted horizontal output transformer?
None of the diodes in this area appear to be shorted.
Looking for suggestions.

Bicycle6228 wrote:

I got a 2SK2761 and put it in.
Power up.
The 2nd anode HV came up OK, but not for long: I heard normal dust crackling
sounds for about 3 seconds, then no HV, no raster, and the SMPS goes into
ticking again.
Yes the new 2SK2761 is now dead shorted.

Did you check the two drivers Q502 and Q503 and IC501?
You'll have to come up with a theory why the first failure occurred,
and then, wether that may have taken other components with it.

Regards,
H.

"Meat Plow" wrote in message
news
On Wed, 28 Mar 2007 21:06:07 -0600, Bicycle6228 wrote:

tick - tick - tick
The horizontal output FET was dead shorted.
The original is a P9NC60, a TO-220 case deal, which has scant info on the
web.
The best resolution datasheet I found is 90% illegible:
http://home.comcast.net/~tomdempster/temp/P9NC60.gif

No matter:
Schematic actually indicates Q504 is a more familiar 2SK2761:
http://home.comcast.net/~tomdempster/temp/m992dell.pdf
Side note however: There are some slight differences between the M992 I
have
and that shown in the schematic; but the horizontal output section seems
to
be indentical.
I got a 2SK2761 and put it in.
Power up.
The 2nd anode HV came up OK, but not for long: I heard normal dust
crackling
sounds for about 3 seconds, then no HV, no raster, and the SMPS goes into
ticking again.
Yes the new 2SK2761 is now dead shorted.

The P9NC60 is a metal tab style TO-220, and it had one of those grey
flexible style insulators at the heat sink.
The 2SK2761 is a plastic case / tab TO-220, so I used the usual thin
layer
of heat sink compound and left out the insulator.

The P9NC60 data sheet [ P9NC60.gif ] isn't legible, and I don't know how
to
evaluate the schematic to determine requirements for a good substitute
for
the P9NC60.
Availability of an actual P9NC60 looks pretty poor (unless I want to
order
1000 of them)
Are there cases where excessive load downstream results in failure of the
horizontal output transistor? A shorted horizontal output transformer?
None of the diodes in this area appear to be shorted.
Looking for suggestions.

I would suspect something in the H-drive took the original HOT out. You
should be using a bit more sophistication in your troubleshooting
techniques for this circuit.

This transistor is likely to be made by SGS Thomson and is actually a
STP9NC60.
If you do a google search for this you will gets many hits and the first one
is a downloadable PDF data sheet, and is perfectly readable. Try it !
Ian.