NEC FS-6390 TV Problem PART 2

Jan 06, 2006 2 Replies

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David 20 years ago

> 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??

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rg26ce1991 20 years ago

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

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David 20 years ago

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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