LG CP-21Q24 not turning on


	FORUM HOME	SEARCH POSTS	WHO'S ONLINE	LOG IN	RULES F.A.Q.

TV Forums: TV Equipment: TV Repair Forum:
LG CP-21Q24 not turning on

Print Thread

alessnilsen
New User

Jun 9, 2015, 2:14 AM

Post #1 of 20 (1949 views)
Shortcut

LG CP-21Q24 not turning on	Can't Post

Hello, new member here!

Happened to find this TV (LG CP-21Q24) in a street close to my house, I brought it and hooked to the AC outlet, but it don't turned on.

When I connect it to the wall outlet, the standby LED turns on, when I press the power button, the TV makes a weird loud noise (the same as 15.73Khz, but very unstable), and after two seconds, turn off being in stand by, if I push the power button again, the cycle repeat.

I looked the two boards (neck and mb) and didn't found any burnt mark or something indicating some damage, so I need help to start and see if I can repair it.

Nothing appears on the screen during the two seconds.

Here some images of the boards:
https://dl.dropboxusercontent.com/...06-08%2012.15.50.jpg
https://dl.dropboxusercontent.com/...06-08%2012.15.14.jpg
https://dl.dropboxusercontent.com/...06-08%2012.14.46.jpg
https://dl.dropboxusercontent.com/...06-08%2012.13.58.jpg
https://dl.dropboxusercontent.com/...06-08%2012.13.44.jpg

Here the TV tself:
https://dl.dropboxusercontent.com/...06-08%2023.11.53.jpg
https://dl.dropboxusercontent.com/...06-08%2023.12.09.jpg

I have a DDM with Hertz and capacitance test (up to 200uF).

Thanks in advance! Smile

Joinville/SC - Brazil

(This post was edited by alessnilsen on Jun 9, 2015, 10:47 PM)

jts1957
Veteran

Jun 9, 2015, 3:23 AM

Post #2 of 20 (1944 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

T801 secondary voltages? Is Q402 heat sink excessively warm? Does Flyback (T402) smoke or have cracks in it?

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 9, 2015, 5:05 AM

Post #3 of 20 (1941 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

The TV doesn't stay turned on enough time to warm any component, so I can't verify that.
The flyback looks fine, I'll try to power it on several times and see if it arcs or smokes, and try measure T801 voltages.

Thanks! Wink

Joinville/SC - Brazil

(This post was edited by alessnilsen on Jun 9, 2015, 5:06 AM)

jts1957
Veteran

Jun 9, 2015, 5:39 AM

Post #4 of 20 (1934 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

Need to determine IF T801 secondary voltages are correct & steady or are changing / pulsating.

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 9, 2015, 2:55 PM

Post #5 of 20 (1922 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

In Reply To

Is Q402 heat sink excessively warm?

Update, after cycling 8 times the power on test, the heat sink of the HOT does get really warm, the other heat sinks on the board still cool.

Here a sample of the noise that the flyback does during startup.
https://dl.dropboxusercontent.com/u/429060/tv-noise.3ga

For now, I found three tensions on T801, 19V, 110V and 12V, when I turn the TV on, the 19V goes to 16V, 110V goes to 82V and the 12V goes to 8V. When off, the tensions are steady and don't oscillate/pulse.

I found that the pins 9 and 10 of the flyback seems to be short circuited, by the circuit of the TV, they aren't connected together.

Joinville/SC - Brazil

(This post was edited by alessnilsen on Jun 9, 2015, 8:06 PM)

jts1957
Veteran

Jun 9, 2015, 7:18 PM

Post #6 of 20 (1910 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

Remove Q402 and see if voltages are full & stable. Might want to test Q402 while removed.

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 9, 2015, 8:31 PM

Post #7 of 20 (1903 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

I removed the Q402, that actually is a 2SD5702 instead of a 2SD2499 and it seems fine, the internal diode is OK and inside it have a 40R resistor, I'll try to make it switch something to see if is fully working.

Turning the TV on without the Q402 does nothing, all the tensions remains the same, without fluctuations.

Joinville/SC - Brazil

jts1957
Veteran

Jun 9, 2015, 8:56 PM

Post #8 of 20 (1901 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

Q402 0TR570200AA KSD5702 BK SAMSUNG TO3PF H-OUT

So Main PS appears fine (with NO load, at least).

Do ANY scan-derived B-Plus sources try to come up?

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 9, 2015, 9:36 PM

Post #9 of 20 (1898 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

Scan derived B+ sources are the secondary tensions derived from the flyback? I'll test if there's any when the circuit is on.

Here my results:

Pin 6 26V: C303 charged with ~12.6V.
Pin 2 180V: C540 charged with ~165V.

All voltages drop when the TV powers off.

Joinville/SC - Brazil

(This post was edited by alessnilsen on Jun 9, 2015, 9:52 PM)

jts1957
Veteran

Jun 9, 2015, 10:03 PM

Post #10 of 20 (1894 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

In Reply To

Scan derived B+ sources are the secondary tensions derived from the flyback? I'll test if there's any when the circuit is on.

Here my results:

Pin 6 26V: C303 charged with ~12.6V. (Across C309)
Pin 2 180V: C540 charged with ~165V. (Across C540)
Pin E25: C51 charged with ~325V (?)

All voltages drop when the TV powers off.

WITH Q402 installed?

Pin 28 IC501 9 volts?

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 9, 2015, 10:31 PM

Post #11 of 20 (1892 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

Yes, without Q402 there's no voltage at those measured points.

Pin 28: C405 measures 12.4V and then 7.8V. (too quick for my multimeter read).

Quote

Pin 6 26V: C303 charged with ~12.6V. (Across C309)
Pin E25: C51 charged with ~325V (?)

So many small numbers to look at.

Joinville/SC - Brazil

(This post was edited by alessnilsen on Jun 9, 2015, 11:03 PM)

jts1957
Veteran

Jun 9, 2015, 10:48 PM

Post #12 of 20 (1887 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

Do you have an Oscilloscope & variable power supply available? WF13, 16, 17 & 18 set powered by Mains? (OR WF13 ONLY - Set NOT supplied with mains, but instead use your own 9VDC into IC501 pin 28)

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 9, 2015, 11:30 PM

Post #13 of 20 (1884 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

I only have a variable power supply available.

So I will feed the IC501 Horizontal VCC with 9V and see if it will have a WF13 at pin 32?

Joinville/SC - Brazil

(This post was edited by alessnilsen on Jun 10, 2015, 12:32 AM)

jts1957
Veteran

Jun 10, 2015, 12:20 AM

Post #14 of 20 (1879 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

Fruitless w/o a scope.

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 10, 2015, 12:33 AM

Post #15 of 20 (1876 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

Done:

Input: 9V
Output: 8.5V
Frequency: 5.12Khz

Quote

Fruitless w/o a scope.

I'll try to get some waveform image of the output.

Joinville/SC - Brazil

jts1957
Veteran

Jun 10, 2015, 1:31 AM

Post #16 of 20 (1874 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

INPUT (pin #28 of IC501): 9VDC (external PS/set unplugged)

OUTPUT (pin #32 of IC501): ? VDC (not sure)
OUTPUT (pin #32 of IC501): ? Vp-p (about 4.5)
OUTPUT (pin #32 of IC501): ? Khz (14.7Khz - 16.9Khz)

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 10, 2015, 2:08 AM

Post #17 of 20 (1872 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

Hmm, I'll try harder.

I used my computer and this is what I got:

Input voltage: 8.71 from external supply.
VDC at output: 8.51V (measured as DC voltage).
VP-P: Unable to measure.
Khz: Main at 15.7Khz.

Image of the waveform:
https://dl.dropboxusercontent.com/...0/imagens/scope1.jpg

It looks the same when running from mains. WF17 looks the same as WF13.

Joinville/SC - Brazil

(This post was edited by alessnilsen on Jun 10, 2015, 6:05 PM)

alessnilsen
New User

Jun 11, 2015, 10:16 PM

Post #18 of 20 (1802 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

I tested as many components I can and I found only one problem, R547 from the ABL circuit was open, so I replaced it, but no luck.

I removed Q13 to see and the TV stayed on, but the screen doesn't lighted up, since the HOT was getting too hot, I don't runn it for more than 30 seconds.

Next pass I'll remove the vertical driver LA7833 that is known to be problematic and see if the TV stay on. If no, I'll start to look at the flyback.

Joinville/SC - Brazil

jts1957
Veteran

Jun 11, 2015, 11:27 PM

Post #19 of 20 (1799 views)
Shortcut

Re: [alessnilsen] LG CP-21Q24 not turning on [In reply to]	Can't Post

You can look at the flyback NOW. Unimpressed

-------------------------
Location: Far, Far Away

alessnilsen
New User

Jun 12, 2015, 3:02 AM

Post #20 of 20 (1797 views)
Shortcut

Re: [jts1957] LG CP-21Q24 not turning on [In reply to]	Can't Post

I'll do. But at this time, I need to see if worth buying a new flyback.

Thanks for the help and patience! Smile

Joinville/SC - Brazil

Print Thread

Search for (options)

- Page loaded in: 0.24 s on (CGI/1.1)