Samsung PN42C450 B1DXZA Doesn't Power On

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

What is the best way to test out a new part before installing to make sure it is good?

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

I disconnected the Y sustain (Y main) and Z sustain (X main) from the logic board and tested Vs resistance on the power board, Y board and Z sustain. The power board and Y board showed in the range of 30K ohms and the Z showed 0 ohms.

I didn't try hooking up light bulbs, but did power on the TV with the boards still disconnected and the chime came on and VS shows 207 VDC, Va shows 53.6 VDC. I didn't check every other connector, but i was getting 15 VDC on CN801 and the 5.3V was showing 5.17V.

This seems to indicate that the power board is good and that the issue is with Z sustain and to start by replacing the two FETs. Is this a correct understanding?

Is it necessary or prudent to check all connector reading?

I am assuming I can reconnect the Y sustain cable, what result would I expect to see once I do?

[R_J]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

You have confirmed the fault is on the Z-sus, and the power supply is working, With the power disconnected, check the VS voltage on the power supply and wait for it to drop near 0 before reconnecting it to the Y-sus

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Is Renesas considered a quality part?

Also I would appreciate some assistance understanding part identification. As i mentioned both transistors are marked:

G
RJH30E2
071B

I am assuming the part is RJH30E2, what do the other markings mean? Also when I google RJH30E2 I get some listings for RJH30xxx, how can I know if these are the same?

[R_J]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Yes Renesas is a good brand, if that is what you are actually getting, the last letters are date code so they will be different

[Andrew F. Ali]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Great!! So you have determined the Z-sus Bd as the faulty culprit. Can you get another working board? I would just go ahead and change the board, but if you want to give the repair a shot we are here to help you. Do as RJ says to let the Vs go down to 0Volts before reconnecting the Y-sus to prevent destroying the board.

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Is there any way to identify the manufacturer like many ICs have a logo? What does the G mean? I was assuming the last four were a lot code or something like that so date makes sense. How can i decipher it? I am assuming 07 is year if so what do the rest mean.

Also I need to better understand the part nomenclature. If i look up "RJH30E2 datasheet" on google I get a variety of information that is not exact, e.g., https://www.alldatasheet.com/view_da...chword=RJH30E2 shows two parts RJH30H1DPP-M0 and RJH30H2DPK-M0. The first one seems more similar to what is in the TV, but I don't know how to be sure if it is correct or even a substitute?

[R_J]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

The original part is obsolete, and my have been a custom number for Samsung.

One of these things is not like the other, one of these things is kind of the same...

The two parts electronic specs are the same, the package and mounting are different
The first is TO-220FL (fully isolated case), the other one is TO-3 (exposed metal flange connected to collector)

Contact Renesas https://en.na4.teamsupport.com/dashboard

[Andrew F. Ali]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

[QUOTE=R_J;850106]
One of these things is not like the other, one of these things is kind of the same...

Sounds like Sesame Street

[R_J]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Sorry 'bout that

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

I waited until the Vs reading was 0 before reconnecting the cables and then waited overnight before turning on the set. I plugged it in and got a click, then hit the power button and got the chime, but i noticed smoke rising up on the left side of the TV back (cover off). I didn't see where it came from, but the stream was long and came from near the bottom of the Y board on the left side which is where the FETs are located. I turned the TV off and unplugged. I waited for Vs to go to 0 and checked the Vs on the power board and the y board and there was no short.

Is it possible it was just some dust or hair that got smoked when power was turned on? The board is a little dusty and with dogs, hair is everywhere.

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Let me add that I never touched the Y board, except to take a voltage reading and that everything was connected, except the X main board.

[Andrew F. Ali]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

OK. So disconnect the X-Main and see if Vs remains steady. If it does then we might be OK. Get another Z-Main Bd.

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Andrew,

You had mentioned that there wasn't a connection between the X and Y boards as far as shared failure. So I had reconnected all the cables except the ones to the X main, it was completely isolated.

I then plugged the TV in and then turned it on when I noticed a wisp of smoke (like after you blow out a candle). I immediately turned off the TV then unplugged and wrote in. Like I said, I wasn't doing anything with the Y board so nothing I have been doing should have caused a problem. Also not sure if turning it off was important as I assume that if something happened it happened and turning if off won't change that, but i felt it was the safer play.

So are you suggesting I should just turn it back on and check things out or is there a different play I should try first?

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Is there a reason not to try turning it on again or should I try to check something out first?

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

The transistors are on order. I was looking further at the Y sustain. There are three resistors that are the same value, 200K ohm-- R5036, R5041 and R5042. 5041 and 5042 read the same, but 5036 reads double.

Can these be read in circuit or do the have to be removed from the circuit?

[R_J]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

If the resistor reads double (400K) it could be bad or something could be throwing the reading off, Too be 100% sure you would need to remove it
Try reversing the meter leads and check it again, if it still reads high it could be close to open.
sometimes if there is a small voltage on the resistor (from a cap elswhere in the circuit) it can cause the meter to read wrong

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

RJ, they are 200K ohms one reads 200K the other two 100K, in both directions. I am reading these off the legs next to the body of the resistor and was assuming that I would be getting the reading through the resistor. As I was thinking about this and I guess if the circuit has a lower resistance than the resistor then I guess I would get the reading through the circuit rather than the resistor. Is this a reasonable thought?

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

While waiting for the parts to come in I looked at the TV again related to the Y Sustain smoking. With it attached there is no Vs voltage, but there was before. I removed all connectors and there was nothing. I attached the logic board and still nothing. I then added the main board back in and the TV powers up -- standby light on, start up chime. Series light bulbs light brightly for a couple seconds then turn off. Hit power on button and the bulbs light up (Vs=207 VDC) and then goes off. Previously without the Y Sustain connected Vs would show 207 VDC and stay on. Now it does not stay on.

Press the power button and the bulbs light for a couple seconds then the standby light blinks 5 time and goes out. The green LED on the logic board blinks slowly. Press power button again and the TV turns off and standby light comes on again.

What is this telling me?

[Andrew F. Ali]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

PSU damage.