NEC FS-6390 TV Problem PART 2

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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??



Re: NEC FS-6390 TV Problem PART 2


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


Re: NEC FS-6390 TV Problem PART 2



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Hello Russell,

Yes, I still have the horizontal white line.

I have checked the voltage on pins 8 and 13, using pin 3 as the ground.

The voltages were as follows:

Pin 8:  0.8v        Pin 13:  0.5v

It appears that these voltages are way too low.

Thanks for your advice on posting new threads, I'll take it on board for
next time.

David




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