Symphonic TVCR-19E1

[Donald]

I'm working on this unit that wont fire up, and when checking voltages I
accidentally shorted Q601 mosfet, 2SK1445.
So replaced it w/2SK1112, replaced D601 that was shorted. Now what I want to
know is what voltage is on the
mosfet drain is suppose to be?.I should never tried to check it in the first
place. Now is there a place in this unit where
the bad solder, or cold solder joint lies. That was the main problem, the
unit would not fire up. The voltage I was
getting on the mosfet drain when I fried it was 161v. So it might have been
running, I dont know. Now Im not
getting any voltage on the drain. Please help if you can, Donald. Email
w/info to [email protected]
Thanks in advance.

 

[Mark D. Zacharias]

If there's no voltage on the drain, then something is open-circuit. Maybe a
fuse, fusible resistor, foil run burned, etc.

Mark Z.

 

[Ol' Duffer]

I'm working on this unit that wont fire up, and when checking
voltages I accidentally shorted Q601 mosfet, 2SK1445.
So replaced it w/2SK1112, replaced D601 that was shorted.
Now what I want to know is what voltage is on the
mosfet drain is suppose to be?.

Drain is switched end of primary winding, so should measure well
over 100 Volts, maybe in the neighborhood of 150~160.

I should never tried to check it in the first place.

Not a problem, per se, if you are careful with your meter probes
and know up front that there is going to be dangerous voltage
present and select appropriate meter range, etc. I would say
there were some other places you should have looked first.

Now is there a place in this unit where the bad solder,
or cold solder joint lies. That was the main problem, the
unit would not fire up.

If you think not firing up must be caused by a bad solder
joint, you may be in over your head. Most of these combos
have supplies that run all the time and only "fire up" by
turning on horizontal drive.

The supply has current limiting and shutdown protection
built in, so having blown it up, these circuits are now
also suspect.

You shot yourself in the foot. Big time. Having said that....

1. On the supply side is usually a fuse, four diodes, a large
capacitor, and a big power resistor. Basic bridge rectifier
setup. The power resistor is there to absorb current inrush
when you plug the set in. Perversely, it sometimes blows to
protect the fuse.
2. When the MOSFET blows, it often takes the gate control
transistor with it. And sometimes other stuff. I don't have
a schematic, so I can't look up D601.
3. These things require finesse, not brute force. If you are
not very familiar, you need to get a schematic and study it
until you understand, or have someone explain it to you.

Believe it or not, the power supply is usually not the problem
in these sets. The most common cause of not firing up that I
see is shorted vertical IC.