Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

[martyparish]

Picked this TV up at the landfill. It had one bulging cap so I recapped the whole psu. I get PS_ON but still no BL_ON.

Upon CLOSE inspection I noticed what looks like a horrible repair gone wrong on the main board! Not really sure, but can you guys check it out?

Check out the pic of the Main board backside. Then look at the SJ stock image.

What the???

[stj]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

it's a splash, the board may have been on the floor of a workshop.
where is the shield?
lots of splash around where that was desoldered too.

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Hmm.. I took off the shield today...

I guess I did it and didn't even notice. argh! Haven't powered it up thankfully. I guess this one is toast anyhow, unless you guys have any ideas on this main board.

Thanks for the reply stj!

[stj]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

so what else happens?
standby led?
audio?
if you force the BL_on signal does the panel light up?

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Sorry for leaving that out.

Upon plugging in, the red led flashes 5 times, pauses for a while then 5 times again.(continually)

Forcing BL_ON does indeed fire up the backlights.


Thanks again!

[ReeceyBurger123]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Heat mobo with a hair drier see if it works.

[Agent24]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Are all the regulators on mainboard working?

[stj]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

5 flashes is clearly a fault-code.
anybody got a service manual?

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Thanks fellas. I tried hairdryer a couple times but not since removing the shield. Will try again.

I'll also check regulators and reports back.

Thanks for helping.

[vinceroger69]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

5 flashes is clearly a fault-code.
anybody got a service manual?

Im pretty sure samsung lcd dont use error codes from the threads ive read over time.

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

I think you are right Vinceroger69.

I do have the service manual and there is nothing about blink codes in it.

I did not notice the (fairly thorough)test points in the troubleshooting guide before, so I am going through them now. Some of these components are HARD TO FIND!

[tom66]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Im pretty sure samsung lcd dont use error codes from the threads ive read over time.

Yeah, they don't (except on the plasma control boards.) It's just power cycling.

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Making some progress I think. Following the SM troubleshooting I got to this:

Does proper DC B9V, B8V,
PANEL_VCC,B3.3V_1
appear at C106, C107,
C121,C131?

Well, all checked out EXCEPT "PANEL_VCC" at C121. Zero volts there. (not sure what panel_vcc should be, but not zero I assume).

The manual also says(if "no"):

Check IC100,D100,IC101,IC103
Change the Main Ass'y refer to Parts list

Assuming the parts are listed in order with the voltage checks(it appears that way), then I need to check IC101.

IC101 is:
FDS4435BZ_F085
P-Channel PowerTrench® MOSFET
-30V, -8.8A, 20m


I'm not sure how to test this. Any tips are appreciated!

[tom66]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Locate the drain, source and gate pins (refer to datasheet)

The source should be ~13V (it's the input, for PANEL VCC will be 12-13V input.)
The drain is the output. When the MOSFET is working and turned on, this should measure 13V. If it is not turned on, it will measure a much lower voltage.
The gate needs to be at least 5V *BELOW* the source to turn on the MOSFET. In other words, the gate-source voltage needs to be -5V or more (-5V to -20V is a typical range) and the gate-source voltage is measured between gate and source pins.

For example, if the source is 13V then the gate needs to be 8V or less to ensure the FET is saturated correctly. (Anywhere from 0V to 8V would be acceptable)

P-Channel FET works with a NEGATIVE gate-source voltage (remember "oPPosite of Positive")
N-Channel FET works with a POSITIVE gate-source voltage (remember "Not Negative")

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Good stuff Tom thanks! That helps greatly.

Wow man 30,000+ posts!!! You've helped a lot of people!

This part is on the bottom side of the board Hope I can find test points on top side...

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Not sure if I did this right. I measured S D and G each from the chassis ground. Was that right, or should I be measuring from D -S or G - S?

Here's what I got from each pin to gnd:

Source: 5.4
Drain: 0.0
Gate: 5.3 (I soldered a wire from G so I could test from top)

Tom, how did you determine that the Source should be 13v? (only getting 4.4v)


Thanks!

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

I'm attaching part of the schematic that I believe is the circuit in question.

Trying to figure out why the source on the mosfet is low(5.4v). Tom says it should be 13v and it has a 25v cap on that line so I agree(not that I'd doubt you guys anyway lol).

Any help from you pros and/or super smart folks is apreciated!!

[budm]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

What is the power supply board P/N? BN44-?????
PANEL_VCC is the DCV for feeding the T-CON board through a switched MOSFET, which usually around 12VDC.
What DCV do you get at the connector of the power supply board that feed the main board? Please give the list of readings and pin name and numbers for each pin.

[martyparish]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

Thanks for the help budm! And others!

BN44-00156A

PIN LABEL VALUE
---- ------ --------
1 ON/OFF 4V
2 N.C. 0
3 GND 0
4 GND 0
5 GND 0
6 GND 0
7 12V 11.9V
8 12V 11.9V
9 GND 0
10 GND 0
11 GND 0
12 GND 0
13 5.3V 5.4V
14 5.3V 5.4V
15 5.3V 5.4V
16 5.3V 5.4V
17 GND 0
18 GND 0
19 13V 12V
20 GND 0
21 13V 12V
22 13V 12V
23 N.C.
24 N.C.



1 GND 0
2 ANA_dimming 3.5V
3 PWM_dimming 4.2V
4 SW_inverter 0
5 STB_5V 5.1V

[budm]

Re: Possible sabotage?! Samsung 32" LNT3242HX/XAA LNT3242H

You can trace out the Source pin, it should lead back to the either 12V or the 13V terminal of the power connector.
The service manual has the diagram for the main board?
But since you are missing the BL-ON (4 SW_inverter 0) so I do not know if it is related to the T-con is locking out the backlights from coming on not due T-CON is not getting the correct Voltage to run.
BTW, we can look up the LCD panel spec to see if the T-CON is running on 5V or 12V just to be sure, but right now that MOSFET is not being turned on due to the GATE Voltage is almost the same as the Source Voltage, it is turned OFF right now. If you use 1K resistor between GATE and Ground then you should be able to force on that MOSFET.