NEC FS-6390 TV Problem PART 2

[David]

I have repaired a few FS-6390 with this problem.
Most likely IC401 is crook, this is a LA7838 vertical output chip.

Also check,
R522 2.7ohm 2w fuseable.
R523 2.2 ohm 1/2w fuseable.
R427 100 ohm 1/4w fuseable.

Replace:-
C609 100uF 16v
C533 2.2uF 160v
C611 22uF 25v
C411 100uF 35v
C607 220uF 10v

Russell Grifiths.

I have replaced these components and still no go. I also noticed that D401
(Fast recovery,Si.,General Purpose,3 Amps at 600V) was also dead. I
replaced it, but still to no avail.

Could I have killed the new output chip by not diagnosing the crook diode
before placing the chip??

 

[rg26ce1991@hotmail.com]

Greetings David.
I have just looked at the schematic and I don't think the shorted D401
would have caused IC401 to fail. But I can't be 100% sure about that.

Do you still have the horizontal white line across the middle of the
screen?

Do you have around 27v at pins 8 and 13 of IC401

Below are the voltages on the schematic for IC401.

PIN Voltage
1 12v
2 7.3v
3 0v
4 6.1v
5 0v
6 5.9v
7 5.8v
8 27.2
9 2.3v
10 n.c.
11 0v
12 11.2v
13 27.7v

I have a FS-6390 on the bench at the moment.
This one went out with a bang.
A piece of IC601 (STRS6708) blew out of the chip, and several other
parts failed nearby.

Just a little helpful advice. If you have more to add about a previous
posting, continue the thread that has already been started.

Russell