Philips 40PFL3505D/F7 Question about FET replacment

[kevinm34232]

Hi, was told this TV was damaged by lightning. Unfortunately after I got it home I noticed someone had been tinkering inside already. Good lesson to check the screws in the back before hand.

Anyways I found a shorted transistor, Q601 that has part # 2SK3798.
http://www.digikey.com/product-detai...QM)-ND/2062700

I can get that part used on ebay or from China, but Im wondering if this one would be a safe replacement:
http://www.digikey.com/product-detai...4QM)-ND/871460

The main thing I see different is it's rated for 3A current as opposed to 4A on the original. Thanks for any input!

[budm]

Re: Philips 40PFL3505D/F7 Question about FET replacment

It need to have the same or better, not lower spec than the original. This two-transistor switching power supply when it goes bad, the MOSFET, the small transistor, Zener diodes, Diodes, opto in that section need to checked.
Same circuits used in Emerson/Sylvania. Also the rectifier diodes in the cold side.

[tw2005]

Re: Philips 40PFL3505D/F7 Question about FET replacment

This would be closer (5A) and sold min qty 1,

http://www.digikey.com/product-detai...5QM-ND/1692460

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Thanks!

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

I've been working on this on and off for a bit now..

Here's what I've done so far..

After trying to repair the original PS board with no luck I decided to order a new one since someone attempted repair before and I didn't know what had been done and diodes were missing, etc.

The new board came and when plugged in some diodes shorted again. I wasn't able to use light bulb method on this one as it kept clicking relay and shutting down.

Long story short I eventually determined the digital main board had a short on the P-ON+3.3V line that was causing the damage to the PS board.

I replaced digital main board and the shorted diodes on the new PS board and finally the TV started up, backlight came on but no video.

So I pulled the T-Con and the fuse F1 was blown, to the left D1 shows shorted in circuit as well as several of the caps above. Im guessing the lightning took out D1 before the fuse blew but haven't removed it yet.

I've put too much $ in this one so far and although I can get the T-Con for around $20 I'd like to try to replace the fuse and diode, if it turns out the diode is bad.

But looking at the markings on the diode all I can make out is a BK and either LL or and F.

Anyone have info on this diode? T-Con Part # is Samsung LJ94-03281G. Thanks!

Im hopeful I can repair original PS board now that I've found the underlying issue and recoup some $.

This is most extensive damage I've seen to a TV it basically caused damage to diodes and a transistor on power supply, a diode on jack board, main board, and now t-con..

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Update:

Removed D1, it is shorted. Short went away on board. Just have to find a suitable replacement now.

Hoping someone has had this problem before!

[budm]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Is D1 Cathode (band side) connected to the fuse? I see the Anode is connected to Ground. If it is connected to the fuse, then it can be just plain diode to protect reverse power supply polarity connection, or it can be TVS Diode in case the feeding voltage is too high.

[tw2005]

Re: Philips 40PFL3505D/F7 Question about FET replacment

smaj14a

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Thanks guys found the diode..

As far as the 3A fuse goes, what does the voltage rating need to be, just anything over 12V? And Fast or Slow blow?

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Use type "T", time delay.

[budm]

Re: Philips 40PFL3505D/F7 Question about FET replacment

twice as much or more, it has to do with arc over the open junction when the fuse blow, it must not be able to allow the arc to jump over the open fuse element. I use PICO II fuse rated at 125V.

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

It's 12V DC... is there much chance of the arc not extinguishing if the fuse is rated to at least 12V DC?

[budm]

Re: Philips 40PFL3505D/F7 Question about FET replacment

I never use or find any fuse rated at 12V, the lowest is the 32V for automotive fuse. I always spec in twice as much if it is available.

"Are ac and DC Fuses the Same?
Direct currents are very difficult to stop or interrupt
when compared to alternating currents. Alternatingcurrent sources reverse the flow of current 120 times a
second (in some locations 100 times a second on 50
Hz systems). Each time the current reverses, it goes to
zero in magnitude. A zero current is very easy for a
melting fuse to stop or interrupt—it is already stopped,
and there is no force trying to sustain an arc across the
fuse element.
DC currents, as the name implies, are currents that
travel in one direction only. They do not reverse. Fuses
bear the entire burden (with no help from the current) of
acting to stop these currents. The internal elements of a
fuse must react to an overcurrent condition (usually by
melting) and as they react, they must do so with
enough capability to interrupt the current from flowing
while extinguishing any arc that might form. DC fuses
are relatively sophisticated devices that have many
different internal elements that must work together. The
complexity of DC fuses makes them cost more than ac
fuses that may contain only a single, meltable link."

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

So I ordered the T-Con parts

1 3 SMAJ14ALFCT-ND DIODE TVS 14V 400W UNI 5% SMA
2 3 F1659CT-ND FUSE 125V TIME-LAG 3A SMD

In the mean time I put a 5A 72v fuse in the T-Con I had from a bad inverter board to test it with the shorted diode removed and the TV is finally working!!

Thanks everyone for helping!

[budm]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Glad to hear nothing else was damaged, so it is 14V TVS diode.

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

I put the old PS board in and TV clicks on with no backlight, then clicks off. Something else is still wrong with that one unfortunately.

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Hi could use some help here on the inverter section, I have all other voltages but the 24v to inverters. Was looking for the 345V, I tested cathode of D1607 and D1609 and have 114V, is that where I should have 345V?

I also have 17V to VCC of IC1401.

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

114V AC, or DC?

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

DC, I found I do have 345V dc on cathode of D1606 though

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

I also have the 345V to the center pin of Q1701 but nothing on the other pins