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From: "Bicycle6228" tdempster at westgatesoftware dot on 28 Mar 2007 23:06
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.


From: Heinz Schmitz on 29 Mar 2007 07:12
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.


From: Ian French on 29 Mar 2007 14:02

"Meat Plow" <meat(a)meatplow.local> wrote in message
news:pan.2007.03.29.16.20.02.575878(a)nntp.sun-meatplow.local...
> 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.


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