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Crumbtrail TV Forums: TV Equipment: TV Repair Forum:
RCA 32" LCD (L32HD31) no sound/picture - orange LED only

 

 


jer989
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Dec 5, 2011, 2:14 AM

Post #1 of 10 (11174 views)
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RCA 32" LCD (L32HD31) no sound/picture - orange LED only Can't Post

Hi-

I have a 32" RCA LCD tv (model L32HD31) that died last year after only about being a year old (so it was purchased in 2009 approx.) One day it wouldn't turn on and only the led on the front lit up amber/orange. No picture or sound (or backlight that I could see either).

I took it apart and now with everything except the LCD controller hooked up to the control board, the PS has no voltage out of it except for 5V standby (5VSB). Even after pressing the TV's main power on button (but I did see that when I had it apart that the front LED went from orange to now green at aleast?!!)

Ther other supplies out of the PS board ar 24V to the inverter board, and 12V to the controller board. Should the 12V and 24V always be on or are those suplies only turned on by a signal from the controller board coming in? How can I figure out if my problem is the PS board or controller board?

There are no bad looking caps, the PS board fuse is ok, no burnt looking components anywhere...

any ideas about what to look at next?

thanks for any suggestions!



jts1957
Veteran


Dec 5, 2011, 3:17 AM

Post #2 of 10 (11170 views)
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Re: [jer989] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post


Quote
those suplies only turned on by a signal from the controller (MAIN) board coming in? How can I figure out if my problem is the PS board or controller board?


See if the 12/24V come up if you supply an external enable voltage (3.3 to 5 volt)(try with Main board connector (the one with 5 volts standby) both plugged in and unplugged.


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Location: Far, Far Away


jer989
New User

Dec 5, 2011, 4:59 AM

Post #3 of 10 (11162 views)
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Re: [jts1957] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post

I did see that there are two connectors on the PS bd. One to the controller bd and one to the inverter bd. The conn. that goes to the controller bd. has a line marked "PW" that is, I assume, the line you're suggesting I try to enable the 12/24v supplies with?

There is another signal that is common to both connectors "BL_ON" - is that a signal to the inverter bd, or a signal from the inverter bd? Thanks for your help!


jts1957
Veteran


Dec 5, 2011, 5:30 AM

Post #4 of 10 (11160 views)
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Re: [jer989] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post

"BL_ON" is used to tell the inverter board to turn the BackLights ON. See if it is leaving the Main board, "passing through" the power supply board, then continuing on to the Inverter?

The connector that goes to what you are calling the controller bd (I'll prefer to call it Main) should have a enable line on it to turn the power supply 12/24 volts on (check both ends for labels. PW "usually" stands for Pulse Width.


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Location: Far, Far Away


jer989
New User

Dec 5, 2011, 5:52 AM

Post #5 of 10 (11157 views)
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Re: [jts1957] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post

Well, i can tell you that the only signals that pass through from/to the inverter bd. and the main bd. (that is, they pass through on the PS bd. but don't go anywhere other than to those two connectors), are BL_ON and DIM.

The only singnal that is on the main bd. conn. on the PS bd. is that PW signal. That signal does look like it goes through an opto to the AC side of the PS bd. and I assume enables the 12/24v supplies. Does that sound correct to you?

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jts1957
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Dec 5, 2011, 6:15 AM

Post #6 of 10 (11155 views)
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Re: [jer989] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post


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Does that sound correct to you?

NO

What is the nomenclature on each of the pins of the connector that goes from the PS to the Main? (BL_ON, DIM, PW, at least one ground & 5VSB so far).


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Location: Far, Far Away


jer989
New User

Dec 5, 2011, 6:20 AM

Post #7 of 10 (11153 views)
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Re: [jts1957] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post

The signals on that connector are DIM, 5VSB, BL_ON, PW, multiple 12V, and multiple GNDs. I'm pretty sure that's it!


jts1957
Veteran


Dec 5, 2011, 6:38 AM

Post #8 of 10 (11150 views)
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Re: [jer989] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post


Quote
See if the 12/24V come up if you supply an external enable voltage (3.3 to 5 volt)(try with Main board connector (the one with 5 volts standby) both plugged in and unplugged.


See if the BL_ON & PW have any voltage on them - in standby and when power button has been pressed.

If neither have any voltage on them, try putting an external 3.3 to 5 volt on them momentarily (one or two seconds, one at a time) to see if backlight or PS 12/24volt come on.


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Location: Far, Far Away


jer989
New User

Dec 5, 2011, 4:04 PM

Post #9 of 10 (11145 views)
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Re: [jts1957] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post

The BL_ON line on the PS board only runs between the two connectors - so I didn't bother putting a voltage in there. I have the PS board on the bench by itself and I did try to put 3.3V and 5V into the PW line. I never did see either the 12V or 24V supply come up, but I was able to trace that signal through the secondary (low voltage) side of the supply up to the opto that signals over to the high-voltage side of the supply and that signal does get up to the opto input ok.

However, on the other side of that same opto, there is no voltage there either when my ext. 5V is on or off. I then checked the Vcc pin on the switcher IC (it's an ST L6599D chip)- -and there is no voltage there ever. (It should be ~17V according the datasheet - shows a 17V zener in the chip itself). The standby pin on that IC is what I checked first, that's what that opto is signalling to - and obviously without a Vcc for that chip- that standby pin on that IC never moves either.

So it looks like it's power supply board I think....


jer989
New User

Dec 5, 2011, 11:00 PM

Post #10 of 10 (11131 views)
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Re: [jer989] RCA 32" LCD (L32HD31) no sound/picture - orange LED only [In reply to] Can't Post

...yes! It was the power supply board!

I was on the verge of ordering a replacement board (~$60 on ebay) and I googled around a bit more and found this post: http://www.fixya.com/...7342941-turn_32_inch

The culprit was a polyfuse that apparently opened and stayed open. Turns out that I had tested this little 1206 part earlier (it is unmarked except for a 'C' marked on it) - and I had measured it as an open - but I didn't know that it was a polyfuse! Turns out that the part in question is a polyfuse (also known as a resettable fuse) which apparently acted less like a resettable fuse and more like a fuse! The part didn't look damaged, the area around it wasn't burned, brown, etc. But that was the root cause of the failure of the PS board.

I believe this is the original part: http://www.newark.com/...00ma-1206/dp/05M2300

As soon as I replaced it with a similar part (the original part was a 200mA part, I had a 230mA part on-hand) - it worked. The board did need the external 5V applied to the PW line into that board, but once applied, both the 12V and 24V supplies came up perfectly.

Thanks for all of your help & suggestions.

I do have to get the whole TV back together, but I'm thinking it should probably work ok, now.

(This post was edited by jer989 on Dec 5, 2011, 11:11 PM)

 
 
 


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