Daewoo Model DP-42SM won't turn on

[tieny]

Hey guys, so I just got this Plasma TV Daewoo DP-42SM that won't turn on.
I plug it in and press the power button and only the red LED shows up.

I looked around the boards for bad capacitors. I'm not sure but the biggest capacitor on the power supply board seems to feel a little domed compared to all the other capacitors. Where should I start with this? thanks!

[tom66]

Re: Daewoo Model DP-42SM won't turn on

Just be aware, it's an 853x480 panel - not HD. Price your repair accordingly, given that these TVs get sold for around £60 each.

Those caps do look like they're bulging, which is an uncommon sight as they are not under much stress. So the set is probably well used. However, it's more than likely not those capacitors at fault - as far as I understand, the TV won't recognise the power button being pressed? That's more of a main rail problem.

Check standby voltage is good & stable. Check any LDOs and fuses on the main board.

[tieny]

Re: Daewoo Model DP-42SM won't turn on

Which components would I check for the standby voltages?

As for the main board, I'm still trying to understand the difference between the main board and the power board. The power supply board usually contains the huge capacitors and transformers and the main board usually contains the main processor I'm I correct?

I checked 3 fuses I seem to see and they seem good (0.4 ohms). As for LDOs, those are a type of regulators right? Which are the LDOs and how do you know when a regulator is bad? Sorry I'm still new and recently taken an interest in circuits and I'm trying to learn as much as I can. =) Thanks!

[tom66]

Re: Daewoo Model DP-42SM won't turn on

Post a close up picture of any connectors going from the power supply to the main board or input board.

Regulators (LDOs) can be tested when power is applied. They take an input voltage (relative to ground) and drop it to an output voltage. Common voltages are 1.2, 1.5, 1.8, 2.5 and 3.3. If the voltage isn't within 2% of one of these, then something is probably wrong. Also output voltage is usually indicated on the device. Post a detailed over head picture of the main board and me or someone else can highlight the LDOs.

[tieny]

Re: Daewoo Model DP-42SM won't turn on

I found 5 connectors going out of the power supply board to the main board as shown in the first 2 photos.

[tieny]

Re: Daewoo Model DP-42SM won't turn on

Here is the board with the inputs

[tieny]

Re: Daewoo Model DP-42SM won't turn on

And I found the service manual for my model. It should be the NEC model. http://www.servicetron.com/daewoo-dp42sm.html

[tom66]

Re: Daewoo Model DP-42SM won't turn on

Are there any labels near each pin, indicating what each voltage is?

[tieny]

Re: Daewoo Model DP-42SM won't turn on

Couldn't seem to find the labels on the main or psu directly but there are labels on the brown board. What is this board called just wondering? Is it still part of the power supply board? Can't seem to make out some of the labels.

[tom66]

Re: Daewoo Model DP-42SM won't turn on

Probably the sub PSU. I see it in Toshiba TVs and Panasonic TVs a lot. It is sometimes cheaper to generate one voltage, and use the sub PSU to step it down.

Check the 5V voltage labelled there. Also check Vs and Vadd.

[s_henya]

Re: Daewoo Model DP-42SM won't turn on

im no big expert, but try replacing the left 2 caps in the first picture,
they looks bad, its an easy and cheap fix so you got nothing to lose.
good luck!

[tieny]

Re: Daewoo Model DP-42SM won't turn on

Do you mean the 2 largest capacitors? Do you recommend changing it tom?
They are labeled Nippon Chemi-Con 200V 1500uF and measures about 1.375" in diameter.

I took the measurements with everything still connected:
I turned on the TV, (power red LED on)

Vs: Started at 0.22 V and slowly increasing (0.293 V after a couple of minutes)
Vadd: Started at 0.22 V and slowly decreasing (0.196 V after a couple of minutes)
5V pin: 0 V

When turning off the TV the measured voltages discharges and decreases extremely slow (Not sure if thats relevant).

[tom66]

Re: Daewoo Model DP-42SM won't turn on

Do you mean the 2 largest capacitors? Do you recommend changing it tom?
They are labeled Nippon Chemi-Con 200V 1500uF and measures about 1.375" in diameter.

I took the measurements with everything still connected:
I turned on the TV, (power red LED on)

Vs: Started at 0.22 V and slowly increasing (0.293 V after a couple of minutes)
Vadd: Started at 0.22 V and slowly decreasing (0.196 V after a couple of minutes)
5V pin: 0 V

When turning off the TV the measured voltages discharges and decreases extremely slow (Not sure if thats relevant).

I don't think they would cause this fault. Change them later, though. They are pretty expensive - £5 or so each.

Clearly the TV isn't switching on for some reason, so I would check for a pin labelled STBY or ON_OFF. As you have an LED lit you probably have good standby voltage but look for a 5V or so source (check all pins on PSU.)

[tieny]

Re: Daewoo Model DP-42SM won't turn on

I was able to found voltages of 5.09V and 4.75V and traced them back.

STB5V was measured to be 5.09V
LED_P was measured to be 4.75V

P12V measures 0.95V and all other pins measure 0V.

[tom66]

Re: Daewoo Model DP-42SM won't turn on

I was able to found voltages of 5.09V and 4.75V and traced them back.

STB5V was measured to be 5.09V
LED_P was measured to be 4.75V

P12V measures 0.95V and all other pins measure 0V.

Okay, so the standby is probably good. Is there a pin marked ON/OFF, STBY, PWR or similar?

[tieny]

Re: Daewoo Model DP-42SM won't turn on

I can't seem to find anything similar labeled, not on the same board at least. I'm looking at the other connectors on other boards and can't seem to find it either.

These should be all the labels on the same board with STB5V

[tieny]

Re: Daewoo Model DP-42SM won't turn on

Looking on the service manual, I can't seem to find it either. However on page 20 of the service manual, it states that there is a STB 5V pin and a PWR_CTL pin on the third photo (the connector with 5 pins) but there doesn't seem to be any labels on it showing which.

[tieny]

Re: Daewoo Model DP-42SM won't turn on

Heres page 20

[tom66]

Re: Daewoo Model DP-42SM won't turn on

It's probably PWR_CTL. Does this line do anything when the TV is powered?

[tieny]

Re: Daewoo Model DP-42SM won't turn on

Tracing back to th main board it goes to the line shown in photo 1 of post # 14 stby5v measures 5.09v and led-p measures 4.75v the other pins measure zero