Dynex LCD won't power on - AVS Forum
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post #1 of 17 Old 01-18-2012, 03:39 PM - Thread Starter
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I'm trying to salvage this Dynex DX-L40-10A LCD HDTV that no longer has picture or sound/audio upon powering it on. The power LED lights up but nothing comes on the display. I've opened up the TV but couldn't see anything wrong with the naked eye (my area of expertise is computers, not TVs/electronics). A little research on this issue yields suggestions to replace the backlight inverter (http://www.usefulparts.com/index.php...oducts_id=1153) or main board (http://www.partstore.com/Part/Best+B...22917/New.aspx), but obviously this is a cheapo TV and don't want to spend too much money reviving it (especially since I'll be donating it when fixed).

Any idea what the problem is? If not, any tips on how I can go about diagnosing this myself?


P.S. - I do have a voltage meter on hand
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post #2 of 17 Old 01-18-2012, 04:03 PM
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IMO, if there's no audio, then there's possibly more than just an inverter problem.
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post #3 of 17 Old 01-18-2012, 04:46 PM
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From your symptoms, I strongly suspect the power supply boad.

The supply will have a 5 volt standby circuit that's always on (e.g. 24x7, lights the led and responds to the power on switch, front panel/remote, which will then turn on additiona power circuits).

The remaining circuits are at least 5 volts for the main logic, 12 volts for the audio and black light inverter (some sets also have a 4th circuit of 16-18 volts).

Since you have a voltmeter, check the output voltages (the voltage will be silk screened on the board at each of the output connectors).

Fixed a Dynex this summer that had a blown $50 cent pico fuse (looks like a resistor) on the circuit that supplied the audio and inverter voltage. However, a failed voltage output could be any component in that part of the supply (a semiconductor, resistor, capacitor etc.).

If you can verify the power supply board is the culprit, they are pretty easy to change out and you should be able to find a replacement board for +/- $50.
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post #4 of 17 Old 01-19-2012, 03:00 PM - Thread Starter
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Quote:
Originally Posted by Ratman View Post

IMO, if there's no audio, then there's possibly more than just an inverter problem.

Well, I haven't tried any inputs yet so I don't know if the audio is actually out too. There's no information overlay displaying at all (i.e., HDMI 1, TUNER, COMPONENT 1, etc.) so that's why I posted my original question.

Quote:
Originally Posted by thiao View Post

From your symptoms, I strongly suspect the power supply boad.

The supply will have a 5 volt standby circuit that's always on (e.g. 24x7, lights the led and responds to the power on switch, front panel/remote, which will then turn on additiona power circuits).

The remaining circuits are at least 5 volts for the main logic, 12 volts for the audio and black light inverter (some sets also have a 4th circuit of 16-18 volts).

Since you have a voltmeter, check the output voltages (the voltage will be silk screened on the board at each of the output connectors).

Fixed a Dynex this summer that had a blown $50 cent pico fuse (looks like a resistor) on the circuit that supplied the audio and inverter voltage. However, a failed voltage output could be any component in that part of the supply (a semiconductor, resistor, capacitor etc.).

If you can verify the power supply board is the culprit, they are pretty easy to change out and you should be able to find a replacement board for +/- $50.

What were the symptoms with the Dynex you fixed?

Can you post a link to a picture of silk screen connector thing?
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post #5 of 17 Old 01-20-2012, 09:52 AM
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Quote:
Originally Posted by DiGiTY View Post

What were the symptoms with the Dynex you fixed?

Can you post a link to a picture of silk screen connector thing?

No audio and picture.

Top left edge of PCB, the connector is removed with only pins showing (this board is appartanly for your model).

The sik screen is just the printing of information on the PCB.

http://assets.shopjimmy.com/media/ca...j/sj122904.jpg

IMHO, the power supply board is pricey for a 2nd tier brand TV and given today's prices.......might be time to upgrade to a new HDTV.
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post #6 of 17 Old 01-20-2012, 02:53 PM - Thread Starter
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Can you send a link to the product instead and tell me which image to click? The link you posted doesn't work (looks like that site has direct linking disabled or something).

Thanks
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post #7 of 17 Old 01-20-2012, 03:15 PM
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I tested the link before sending and it worked.......probably because it was still in my browser cache.

If you go to the URL root and do a seach for your model, you'll find it.

http://assets.shopjimmy.com/
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post #8 of 17 Old 01-20-2012, 04:09 PM - Thread Starter
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Found it! So I just touch my voltage meter on the copper wires of those donut looking things on the bottom right of the board (that's the only place I see voltage information)? Should the TV be on, off, plugged in or unplugged?
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post #9 of 17 Old 01-21-2012, 07:05 AM
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No......this is only general information regarding the power supply's input/output specifications (e.g. 240 volts in at 50/60 Hz, outputs are 5, 12 and 24 volts).

Stay away from this area (high voltage and current present). I already said where the outputs are located. However, the voltage levels (5,12,24,ground) for each pin do not seem to be marked on the board.

Based on your second question, it's time to call the repairman or go shopping.
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post #10 of 17 Old 01-22-2012, 02:30 AM - Thread Starter
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Quote:
Originally Posted by thiao View Post

Based on your second question, it's time to call the repairman or go shopping.

Great advice and I understand why you say that, but I'm here to learn what I can myself and honestly I'm just a stickler for details. I'm okay with this project being a failure and if it is a success I'm donating or giving this TV away anyway.

I appreciate your help so far and if its not too much to ask; which pins on the top left connectors do I test with the voltage meter?
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post #11 of 17 Old 01-22-2012, 06:51 AM
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OK....the TV should be turned on, not standby (even though you have no picture/sound).

The pins on the board should have a connector(s) with ribbon cable(s) going to the other boards in the set.

Leave the connectors on because various there is a signal sent to the power supply board that turns on the required voltages.

There will always be a 5 volt circuit that is always on (even when the set is off/standby) that powers the front panel LED light. remote control receiver etc. When the set is turned on, a signal is sent that turns on the additional power supply voltage circuits.

The pins will either be ground, 5, 12 or 24 volts) From the board picture, I did not see any markings that identified what level should be at each pin. Don't see this often and a service manual is required to know what level each pin should be at.

All you can do is verify that the power supply board has the needed voltage output levels.

Make sure the meter is set to read the correct voltage and not current, resistance etc..

Attach the negative volt meter lead to a good ground point on the board and use the positive lead to probe each pin. Be careful that the probe does not short any pins together.

If the probing shows that you have 5, 12 and 24 volts the supply is likely OK. Note, some of the pins will read 0 volts because they are at ground potential.

From the symptoms, I would suspect the 24 volts (possibly the 12 volts) missing (supplies the back light inverter and audio ampifier).
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post #12 of 17 Old 01-23-2012, 02:23 PM - Thread Starter
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Thanks! I'll give it a try later tonight
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post #13 of 17 Old 04-28-2012, 04:42 AM - Thread Starter
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I never did get around to testing the voltage thing (I couldn't figure it out - the meter indicator wouldn't move), but I did install a replacement power board. Initially the same problem occurred (blue LED comes on, but no picture, can't power off via remote or TV panel buttons) then through a series of power cycles (unplugging and re-plugging the power cord) the TV came on then shut right off, came on stayed on longer then shut off again then came on, stayed on and then I can power it off myself (via remote and/or panel).

I'm not getting my hopes up that the replacement power board was the solution - others have stated this 'no picture' issue happens occasionally and they perform the power cycle to fix it.

During this recent repair attempt I did find the service manual for the TV (http://www.scribd.com/doc/72513882/D...ual-DX-L40-10A). It states the main board is the culprit so I'll replace that next if the replacement power board turns out to not be the actual fix.

Hope this helps someone out there.
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post #14 of 17 Old 04-28-2012, 04:09 PM - Thread Starter
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Spoke too soon. The unit doesn't power on at all now, back to its old ways. I'm ordering the main board now and see if that'll finally fix it.
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post #15 of 17 Old 10-17-2012, 06:30 PM
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well did it work as I have the same problem
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post #16 of 17 Old 10-18-2012, 01:29 AM - Thread Starter
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I never got around to ordering the main board. I think because it was hard to find it online.
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post #17 of 17 Old 03-19-2013, 09:13 PM
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I am having very similar problems...Dynex DX-L40-10a hd tv... So, I ordered and installed a new power supply board. I turned on my tv and let it sit there for a while with the blue screen up... and it is doing the same retarded crap.

Symptoms- Works properly intermittently, turns off and on randomly, screen blacks out, u-remote hardly works, gota reset it by unplugging/replugging the power cord, sometimes I'll hear a "pop" from the speakers and the screen will black out, sometimes it puts out a really high pitched noise, and once or twice it was putting out an unbelievably loud "white noise sound" and I had to run over and yank the power cord out of the wall before my, or my cats, head(s) exploded...

Why God?... WHHYYYYY??.......
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