Replacement for transistor ON4827?

[Jeroni Paul]

Some time ago a Philips 28ML8805 blew its switching transistor part 7216
labeled ON4827 due to a bad solder joint. The bad solder joint was repaired
but I could not get an ON4827 so I tried a BUT12AF, worked fine but had some
problem starting in a cold morning (heating up the transistor fixes the
problem). Asked this newsgroup and was recommended to find an ON4827.

Tried everything and could not get an ON4827. A shop sold me a 2SC3973A as a
substitute for ON4827, it lasted only 30 seconds and went open. What
transistor can I use for replacement? I repeat I cannot get an ON4827.
Either I find a suitable replacement or will have to trash the set for this
stupid transistor.

 

[Jerry G.]

Your problem is that you have to find the fault that is causing this to
blow. Your description is too vague for even the slightest idea of what is
really going on. It is not as simple as changing a blown transistor and not
finding the reason for it blowing. There is obviously other fault conditions
that are happening here.

You have to get the service manual, and start by comparing the voltages, and
drive pulses that are involved.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
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"Jeroni Paul" <JERONI.PAUL@terra.es> wrote in message
news:c18vod$1g3qin$1@ID-215914.news.uni-berlin.de...
Some time ago a Philips 28ML8805 blew its switching transistor part 7216
labeled ON4827 due to a bad solder joint. The bad solder joint was repaired
but I could not get an ON4827 so I tried a BUT12AF, worked fine but had some
problem starting in a cold morning (heating up the transistor fixes the
problem). Asked this newsgroup and was recommended to find an ON4827.

Tried everything and could not get an ON4827. A shop sold me a 2SC3973A as a
substitute for ON4827, it lasted only 30 seconds and went open. What
transistor can I use for replacement? I repeat I cannot get an ON4827.
Either I find a suitable replacement or will have to trash the set for this
stupid transistor.

 

[Jeroni Paul]

Jerry G. expuso:

Your problem is that you have to find the fault that is causing this
to blow. Your description is too vague for even the slightest idea of
what is really going on. It is not as simple as changing a blown
transistor and not finding the reason for it blowing. There is
obviously other fault conditions that are happening here.

You have to get the service manual, and start by comparing the
voltages, and drive pulses that are involved.

I already did that. The original cause was a bad solder joint that once
fixed the set worked. BUT12 transistors do not blow, so I belive the problem
is not in the set. The resistance of these transistors seems a bit too high
when cold because the set sometimes does not start. Heating the transistor
makes it work.
Maybe will have to try various BUT12 from different manufacturers to see if
some works fine.

PD: There is no electrolytic cap in series. All electrolytics check fine.