Sharp C-1410 no power (smps issue)

[Username1]

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Hi! - You may not have a short, but instead you may have a problem related to one
of the hold down circuits. Low voltage, or high voltage hold down circuit. You can
see on the schematic there is a small winding off the flyback that goes to that
5 pin chip in the power supply. I think it's labeled Impulse, or Trigger.
It's a safety circuit, and this problem is made for service with a
Variac. Set it low and turn the set on and see if it fires up.
Theory is the tv does not develop voltage high enough
to trigger the hold down circuit, and you find the
fault with a volt meter.....

Keep in mind that if part of the tv does not start, with no load the B+
May run artificially high....

The other thing you can do is look at the tutorials on YT for this problem
Search Sharp Hold Down Circuit Troubleshooting - or - similar. For some
reason the Horiz Osc. is starting and shutting off. This tv must have
been made before the Jungle IC. that controlled everything, because
the hold down IC is stand alone by the power supply.......

I don't remember ever having to work on a Sharp Hold Down Circuit
before, so best I can offer is to look at the tutorials on YT, and do
plenty of Google searches on the Sharp Hold Down Circuit tutorials
as there seems to be a few on YT, so there may be some on G.

This tv does not have a switching power supply, but does make
some of the supply voltages off the flyback, A short lived
design.

In this video you can see he finds a bad cap, and talks about
the Protection Circuit and appears to have full B+.

So also search Sharp Protection Circuit maybe add your
model number etc.

https://www.youtube.com/watch?v=7CndoU7Qg-w


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And in this video you can see he found a bad resistor near items labeled D604
which is in the Horiz Output area, Same numbering system as your set.
Open resistor may let some voltages run high if in the feedback to
the hold down circuit.

https://www.youtube.com/watch?v=_Y4G1e7AZGY

And again this title of the video is for the hold down circuit.


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Be sure to check the fusable resistors, and high value resistors,
Diodes, and Zener Diodes as well, because a Zener diode can
be used as a trigger.


Hold Down circuits are very tricky.......



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