Samsung LN32C450 - Audio but no video

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Any last thoughts on this?
Also, if I were to buy a main board must it be the same part # or can I substitute others that say they are compatible for this tv?
Thanks!

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Something else strange has happened. I bought a new main board and installed it. It still would not work. I then disconnected the BLU_ON wire, still nothing. Then I pulled wires one by one til I got to E-PWN. I MUST d/c both the BLU_ON and E-PWN to then get the picture, but i do! Backlight and stream from my PC come through. That's a first.
Why did this happen and is it OK to D/C E-PWN?

[tom66]

Re: Samsung LN32C450 - Audio but no video

So is the behaviour with the disconnected wires the same as with the old main board? Also, what does 24V measure when it's working?

[Aulus]

Re: Samsung LN32C450 - Audio but no video

I'll be around today to diagnose anything that you see fit.
The behavior with the E-PWN and BLU_ON wires d/c is an operational TV = GOOD.
The 24V is still reading 26.6-26.7V.

[tom66]

Re: Samsung LN32C450 - Audio but no video

I suspect an issue with the power board feedback circuit. But can't explain how many board changes that.

[cmeuchel]

Re: Samsung LN32C450 - Audio but no video

Was this problem every solved? I have Samsung LN32C540F2D with similar symptoms. Currently, the backlight is on most of the time, but will flicker and shut down for no apparent reason. Measuring DET_5V shows 0V when working and 1.5 when the backlight is off. When flickering it is about 0.8V. I am assuming my DVM is averaging the signal between 0 and 1.5V. I have replaced the main board (not new, pulled from a unit with a cracked screen) and tested another power supply board. My next thought would be to change out the inverter board ($20 or so). Any comments are appreciated.

[PriorUniform721]

Re: Samsung LN32C450 - Audio but no video

Sorry I can't create my own topics yet but I have the exact same TV.

Problem: Backlight flickering, started out slow and infrequent, now ~2Hz(guess). It used to take 20 mins before it would start flickering, now most times it starts right away.

I've taken the TV apart and see no obviously bad caps then I followed the first rule of troubleshooting, "thou shalt check voltages."

Main input cap: 380V then draining down to 0V.

Main board supply side of PSU:
5Va = 5.2V
13V = 12.56V

Inverter supply:
24V = 24.4V

Other notes/ovservations:
- Audio never cuts out
- Flashlight test shows LCD is working
- I've noticed the upper of the two transformers is making a buzzing sound.

Note: The inverter shown by the OP has 8 separate transformers. Mine has two with what looks like one primary side with two sets of taps for the secondary side.

The inverter board is labeled T871075.00. Some googling shows a Samsung part "27 D042099" maybe.

I wonder are these two inverter board styles interchangeable? From the look of it the board also appears in TVs from other manufacturers.

It looks like:
.

Thank you,
-Alan

[budm]

Re: Samsung LN32C450 - Audio but no video

Check the secondary side of the inverter transformer winding resistance to see how close they are to each others. Look real close at the transformer to see if any one of them was over heated, look at the bottom side of the board to see any over heated section where the board turns brown.
Those two filter caps should also be check for capacitance and ESR.

[PriorUniform721]

Re: Samsung LN32C450 - Audio but no video

Thanks budm for the quick response.

I should have mentioned it before. The board looks good, no discoloration on either side.

I pulled the caps to measure them only to find out my DMM can only measure up to 100uF and two of the caps on the inverter board are 390uF. The meter goes to OL on them. The 47uF reads 51.2uF which is a bit out of a 5% tolerance. I do not have an ESR meter so I cannot check that.

Today after putting the caps back the backlight didn't even come on right away. I thought I had put the caps in wrong or something. I was trying to do the flashlight test again when the backlight came on again and started flickering.

I was going to confirm the behavior described earlier in this thread about how w/ the main board removed the pull-up in the PSU turns the inverter on. I did notice this last night but I wanted to see if the flashing was occuring or not. I was trying to see if perhaps the main board was cycling the BL_ON pin. With my DMM on VDC I am getting 5.2V on this pin when the main board powers up. I am a hobbyist and do not have a scope so is there a way to see if the main board is cycling the BL_ON signal with just a DMM (Extech 430 btw).

The transformers read (both today and yesterday)

Top of board:
Primary: 0.8ohms
Secondary 1: 966ohms
Secondary 2: 952ohms

Bottom of board:
Primary: 0.8ohms
Secondary 1: 906ohms
Secondary 2: 911ohms

So there is a bit of a difference between the two transformers. The top one is reading ~40-50ohms higher.

Am I seeing this right? Does each of the legs of the secondary side go off to a different LAMP which is then presumably grounded on the other end?

If I can determine that the main board isn't cycling BL_ON it might just be worth $15 or so to get the replacement inverter.

Thanks,
-Alan

[budm]

Re: Samsung LN32C450 - Audio but no video

You can look at the BL-ON with DMM it should be pretty solid dc >2.5VDC, as long as it is staying at >2.5VDC it does not matter, you can force on the the BL-ON line using a resistor but you have to disconnect that wire going back to the main board first.
The one that may cause the flickering is the Dimm/E-PWM control line, see post 42, try disconnecting the DIM/E-PWM LINE..
The resistance reading is >3% difference, but that is just a guide.