Transistor Replacement K4112 => K3596

[stormy1777]

On an LCD TV, the power supply board works EXCEPT one area with burning signs, in that area there are 4 diodes all tested OK off board, as well as 2 transistors marked K4112, these tested OK only on 2 pins, so, they are BAD.

I have on hand very similar K3596 transistors, and wondering if this is safe to exchange these two?

I'm planning to just replace and see if that area of the board puts out the marked 24VDC, and if not, find the exact K4112 transistor..

Any tips ? how do I find the exact differences (visually they look the same)

Thanks in advance.

Stormy

[SteveNielsen]

Re: Transistor Replacement K4112 => K3596

You have to check specs on the parts to see if they are close enough. They aren't...

K4112 (2SK4112): Field Effect Transistor Silicon N Channel MOS Type (-MOSVI) Switching Regulator Applications

K3596: S Silicon NPN Planar RF Transistor Applications; RF-ampllfier up to GHz range

[stormy1777]

Re: Transistor Replacement K4112 => K3596

ok, thanks Steven!!

I now see it, in that case, I must've tested the K4112 incorrectly, maybe it is good after all...

Can anyone say? I have no clue how to read the data sheet/specs

Multimeter in Diode position:

1) Positive lead on Source (right most), Negative on Drain (middle) => Reading: 470
2) ALL other combinations show an Open circuit, EXCEPT, see #3
3) Negative on Source, now TAP positive on GATE (left), and put quickly on Drain, the meter drops from ~1600 down to zero and then open circuit..

Does this mean this is a good transistor?

aside from that, not sure what could be wrong, there is the HUGE coil (top left of this photo)



( this is not MY board, but looks identical, near the diodes / top left on my board its a bit brown/ burnt)
Thanks for any tips!!

[stormy1777]

Re: Transistor Replacement K4112 => K3596

Actually, this photo looks more like my board (see brown area on the left side):

[budm]

Re: Transistor Replacement K4112 => K3596

That section is the high Voltage Inverter section for driving the CCFL. there are two POWER MOSFETs mounted on the heatsink.
So those two MOSFETs do not have low resistance readings between S and D pins, right?

[stormy1777]

Re: Transistor Replacement K4112 => K3596

with Multimeter in Resistance settings, ALL pin combinations show open-circuit in all combinations. Only the Diode settings shows signs of life as described above. This is the first time even for me to test such a thing, I tend to think it is OK, despite the burnt signs, b/c I saw on ebay also burnt in that area and folks claiming they are OK boards.

Testing the board's outputs, all except the 24v ccfl yields VDC.. I meant I do not know how to test that BLACK bulky coil on the top left.. not sure if that thing can go wrong.. or maybe it's the huge capacitor.. not sure, I'll try to remove more parts and see


Sorry, hope I don't get yelled that my first thread mutated into debugging a board I was convinced I had the issue, due to the burnt signs on the board, but testing the components they seem OK...

[SteveNielsen]

Re: Transistor Replacement K4112 => K3596

Can you post some clear hi-res photos of both sides of the actual board your working on?

Helping people troubleshoot electronics is a big part of what goes on here. You aren't doing something wrong.

[trebo]

Re: Transistor Replacement K4112 => K3596

have you tested that BF1 fuse, (assuming it is a fuse)

[momaka]

Re: Transistor Replacement K4112 => K3596

Multimeter in Diode position:

1) Positive lead on Source (right most), Negative on Drain (middle) => Reading: 470
2) ALL other combinations show an Open circuit, EXCEPT, see #3
3) Negative on Source, now TAP positive on GATE (left), and put quickly on Drain, the meter drops from ~1600 down to zero and then open circuit..

Does this mean this is a good transistor?

In most cases, YES.

In particular, test #3 above turns ON the MOSFET (when you have black probe on Source and tap red probe on Gate). Some MOSFETs (like on PC motherboards, for example) will stay turned ON and showing zero or low resistance between D-S until you touch the Gate and Source together with your finger (or multimeter probe).

[budm]

Re: Transistor Replacement K4112 => K3596

The 24V has nothing to do with that inverter section.
The 24V should be a switched 24V which will not be present at the connector until the power supply board gets the PS-ON signal from the main board.
So what is the exact make and model of this TV and what is it not doing?
You should tell us he DCV you have on each pin of the the connector CNE1? when TV is plugged in and when the power switch is activated.
Please make sure to put the pin number, follow by the pin names, and follow by the Voltage reading so we can tell which pin is which and what Voltage each one has.

[stormy1777]

Re: Sansui LCT40SD powers ON, but NO backlight

I'll try to reply to all changed subject line to reflect revised topic

1) This is a Sansui 40" LCD TV, model LCT40SD "Sakura", it powers on, but no back light, audio works fine

2) BF1, I have no clue what it is, on Diode mode meter BEEPS showing connectivity, same goes on other similar items, like BC3, BC2, externally appearing similar component, if they are fuse, there is connectivity through them..

3) I've uploaded a few photos, seems the website reduces the size, but it should still be good enough. the photos are:

3.1) Entire board, with burnt area close to the power inverter (huge black square)
3.2) Close up of that burnt area, the diodes and transistors all seem to test OK.
3.3) a photo with the original heat-sink + transistors removed, and "similar" transistors in place, i've now removed these, b/c they are incompatible.
3.4) other area of the board... with large capacitor
3.5) back of board...

4) The CNE2 seems to put out 11.8V (I think only 4 wires are actually connected), so I think that area is OK.

5) The CNF1 puts NO VOLTAGE at all, despite TV in ON with green light in front lit.

6) I'll post the CNE1 measurements shortly.

Thanks.

[stormy1777]

Re: Transistor Replacement K4112 => K3596

CNE1 has 15 pins, with power connected and TV On, the stand by light is NOT on b/c CNE1 15 pin connection is disconnected, for measurements, the voltages are:

LEFT most pin marked 24V, comes at 12v, and drops down as I measure, went down to 6V, and probably more, i just kept going..

Marked:
24v pin 1 - 12V dropping...
24v pin 2 - 0v
12v pin 3 - 0v
12v pin 4 - 0v
GND pin 5 - 0v
GND pin 6 - 0v
BLON/OFF pin 7 - 0v
BLDIM pin 8 - 0v
GND pin 9 - 0v
GND pin 10 - 0v
GND pin 11 - 0v
5.1V pin 12 - 0v
5.1V pin 13 - 5v
5USB pin 14 - 5v
PSON pin 15 - 0v


I'm thinking of getting a use board, but cannot find the EXACT same one..

Mine is marked: pcbada018-20haa US-2004-0155596-A1 GIPST14020HCA Rev.0

I can only find "GIPST14020HAA" or "GIPST14020HBA", these look very similar, with exception of one small extra yellow capacitor at ZNR1 near the power source, between the two coils, and , the connector for CCFL, in the GIPST14020HCA it is in CNF1 (wide), in the GIPST14020HAA & GIPST14020HBA that connector is in CNF1A (narrow)..

For example, an "HBA" board claimed to be working, despite the burnt signs



Do you think I can exchange the CNF1 connector from my bad board to one of these used boards?

Thanks for any tips.

Stormy.

[budm]

Re: Transistor Replacement K4112 => K3596

"NE1 has 15 pins, with power connected and TV On, the stand by light is NOT on b/c CNE1 15 pin connection is disconnected, for measurements"

You have to have connector in place for the valid measurement since the main board will send out command signals to turn on the rest of the power supply and the inverter circuit so we need to find out if the main board is sending the signals or not.

[stormy1777]

Re: Transistor Replacement K4112 => K3596

I'm pretty sure the other board does work, and does send the signals, since the speakers are powered from it, and they work, also it powers on the TV, i.e. standby changes from RED to GREEN by pressing the power on button. That secondary board is on a green board, with low current/voltage, and all capacitors look like new, no damage or anything.

I didn't realize I'm supposed to somehow measure from the TOP while the connector is in-place...

I'm afraid we may never know, b/c a friend came to help and accidentally shorted one of the transistors, while the board was **plugged** .... not good.. so things are a bit blown up.. and I'm not sure I'm up for repairing a broken board to begin with, maybe experts like you, but here it takes time to de/solder, etc. so.. I'm hoping one of the "GIPST14020HAA" or "GIPST14020HBA" boards will make the TV work...

Thanks to all who helped, I'm looking forward to my next adventure!!! this is a fascinating world!!

Stormy.

[fzabkar]

Re: Transistor Replacement K4112 => K3596

Just FYI, the 2SK3596 is a high speed, low Rdson, N-channel, silicon power MOSFET which is specified as suitable for switching regulators.

[Longbow]

Re: Transistor Replacement K4112 => K3596

Questions about MOSFET testing seem to come up every day or two. Perhaps someone with a nifty drawing program can help with a sticky. In general I like to desolder 2 legs of the FET and look at the resistance between S and D. Briefly short S to G to bleed off any residual voltage. Resistance between S and D should show an open circuit. If you see a low resistance, or a dead short such as 1 ohm, it is smoked.

The second part of the test involves putting a little bias on the gate. Use a spare resistor of maybe 100K hooked between the D and G (for an N-channel) or between S and G (for a P-channel) Now the resistance will be low - the transistor is biased on. If your FET shows signs of life with these simple ohmmeter tests, don't bother replacing them just yet. The Failure mode for a MOSFET is usually dead short.

A word about switching MOSFETS. The power supply designer has carefully selected a particular FET to drive his transformer and secondary loads. You CAN get the supply running with different FET's in many cases, but usually not for long. Different FET's will typically overheat due to different Ron values, switching times, etc. This is one place where the original devices should be used. If they are NLA...use your best judgment.

[neilc6]

Re: Transistor Replacement K4112 => K3596

I have a Calypso 40" TV with the same problem. I will start a new thread.

[neilc6]

Re: Transistor Replacement K4112 => K3596

Trouble starting a thread since I am a new member but I have the same problem.

TV is Calypso model CLP-40LC1 40" LCD backlit
Power supply is Greatchip GIPST14020HAA Rev.6

When TV is powered on, indicator LED goes from red to green and backlight flickers on and then shuts off (protection circuitry?)

There is a scorch mark on the white/pink wire from the power supply board to the inverter and the high voltage circuitry on the upper left corner has discoloration. All electrolytic caps are not bulged and look ok.

From this thread, seems like I should replace the transisors mounted on the heatsinks and test the diodes in this area. I have a $15 ESR meter from ebay on the way.

[budm]

Re: Transistor Replacement K4112 => K3596

That big long board on the left is the Balancer Board.
You have power supply/inverter board combination.
The pink/white wires carry high Voltage, 1500~2000V.
Which picture show the scorched mark?

'All electrolytic caps are not bulged and look ok.' Bad caps can look normal.

[neilc6]

Re: Transistor Replacement K4112 => K3596

The scorch is on the full picture of the back where the high voltage wires are taped down(now burnt off) probably from the heat from the wires. There is a burnt electronics smell with the tv on. The FETs I would like to replace are marked K3569 so 2SK3569. Looks like there are various versions of this power supply board.