Sharp Aquas LC-20B2UA random shut off issues.

**PlainBill** · 05-21-2011, 05:32 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Interesting problem. It seems to be a common issue with this model of Sharp Aquos. I find it strange that you have to unplug the power adapter from the wall to get it to 'reset' AND the fuse inside the TV blows. This suggests a double fault - problems in both the TV and the adapter.

Now it's time for the standard suggestion. Remove the back from the TV. Take a single over-all picture of the innards so we can get an idea of the interconnections. Take a second picture of the board with the fuse that blows. Attach the pictures to your next post using 'Manage Attachments' (below the text entry area). Do NOT post the pictures inline. We are looking for good, sharp pictures so we can identify components..

PlainBill

**Village Electronics** · 05-21-2011, 07:26 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Did your friend describe this as a problem before the incident with the ice cream? Was it preexisting or coincidental?

**thisguy** · 05-22-2011, 02:10 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Thanks guys!

I've uploaded the pictures. They started out as 18 megapixels, but i had to shrink it down quite a bit so they were not crazy file sizes. Please let me know if better or more details areas or needed.

btw, The fuse only blew once after I initially replaced it when I got the TV. It has not blown since I have been using the new AC adapter.

Also, I cannot be certain, but I'm pretty sure the random shutting off problem did not happen before the AC adapter was shorted by the ice cream.

Picture one is the overall picture.
The fuse I replaced was F3701 of picture 2.
The rest are just a bit closer up.

Thanks again!

Attached Files

**thisguy** · 05-22-2011, 02:25 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

I also have a service manual

Sorry I had to split it up into 3 parts or it wouldn't let me upload.

Attached Files

**PlainBill** · 05-22-2011, 07:37 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Excellent pictures, and you deserve a lot of praise for the work you did. I wish I could offer some encouragement. The fact is that this is a very early LCD TV with very poor specs. Still, it does represent a challange, so here are some thoughts.

There are two fused power input lines. One is for Vcc.SIG, and runs to both the terminal and main boards. The other goes only to the voltage regulator on the terminal board. It would help if you could identify which of those you replaced.

There are two possibilities. Both assume that the power supply reacted to the ice cream bath by failing high - producing too high a voltage. That voltage surge damaged some component on either the main board or the terminal board.

If the fuse that blew is the one going only to the terminal board, it would be worthwhile replacing the voltage regulator. If it's the one for Vcc.SIG, about all you can do is see if any component seems to be getting unusually warm.

I did check eBay for parts for this TV. There are multiple listings for most of the parts. The only notable part not listed is the terminal board. Even if the problem is the main board, at $60 plus shipping I'm not sure it is worth it.

PlainBill

**fastvideo** · 05-22-2011, 09:07 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

I have the same TV having this same problem.

All fuse are good, AC adapter is good.

It turns off randomly. Sometimes it'll work for days and then sometimes it'll turn off. Or sometimes it stutter, turning off and right back on.

Is any service bulletins for this issue from sharp?

**thisguy** · 05-23-2011, 03:09 PM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Thanks Bill!
Yeah, I figure this TV kinda sucks. I wont feel to bad if I can't fix it. I just figure I try since I sunk 30 bucks into the new AC adapter and because it's been sitting in my room for the last 2 years (also I recently got a soldering station

) I've uploaded a new picture of the fuse that blew. Please let me know if its the Vcc.SIG or the one that goes to just the terminal board. The voltage regulator on the terminal board, is it that IC3701 DC/DC PWM?

If you don't mind me asking, what does the VCC.Sig power vs the just the terminal board?

Also, I just can't understand how if the AC adapter is new (and assuming it's running fine), how any damaged TV component could tell the difference between whether the AC adapter has already been plugged in for a while or if it's been unplugged for a while (because it only turns on after a random shut off if the AC adapter is unplugged from the wall for a while). Is it possible that the damaged TV can be triggering some type of safety function built into the AC power supply? Or perhaps creating some type of instability in the AC power supply that it shuts it down?

Attached Files

**PlainBill** · 05-23-2011, 05:37 PM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Originally posted by thisguy

Thanks Bill!
Yeah, I figure this TV kinda sucks. I wont feel to bad if I can't fix it. I just figure I try since I sunk 30 bucks into the new AC adapter and because it's been sitting in my room for the last 2 years (also I recently got a soldering station

) I've uploaded a new picture of the fuse that blew. Please let me know if its the Vcc.SIG or the one that goes to just the terminal board. The voltage regulator on the terminal board, is it that IC3701 DC/DC PWM?

If you don't mind me asking, what does the VCC.Sig power vs the just the terminal board?

Also, I just can't understand how if the AC adapter is new (and assuming it's running fine), how any damaged TV component could tell the difference between whether the AC adapter has already been plugged in for a while or if it's been unplugged for a while (because it only turns on after a random shut off if the AC adapter is unplugged from the wall for a while). Is it possible that the damaged TV can be triggering some type of safety function built into the AC power supply? Or perhaps creating some type of instability in the AC power supply that it shuts it down?

The 1.6A fuse powers only the audio amp. The fuse you replaced powers the Sig.Vcc line (I had it backwards on my earlier post). On the terminal board it goes to a DC-DC converter which provides 5V, 12V, and -8V. On the main board Sig.Vcc provides power to a couple of DC-DC converters and the 'Operations Board' (the board with the push buttons). And it may go to other points. I don't even pretend to myself to be infallible.

You bring up a very good point. Perhaps you can verify it. From an electrical point of view, there should be no difference between unplugging the AC adapter from the wall and unplugging the AC adapter from the TV IF the adapter was putting out the proper voltage. If you can leave the TV open so you can access the two fuses (without any chance of fingers touching the inverter area), you should be able to determine if the DC input voltage is still present when the TV shuts down.

PlainBill

**alexanna** · 05-24-2011, 04:16 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Originally posted by thisguy

Also, I just can't understand how if the AC adapter is new (and assuming it's running fine), how any damaged TV component could tell the difference between whether the AC adapter has already been plugged in for a while or if it's been unplugged for a while (because it only turns on after a random shut off if the AC adapter is unplugged from the wall for a while).

It will start after the external power supply is unplugged for a while and plugged back in, well with the power supply plugged in its generating some heat inside the television. Wonder if there may be a problem with the standby circuit possible poor soldering.
A question I would have is if the standby power failed while the set was running would that cause a shutdown?

**thisguy** · 05-24-2011, 12:53 PM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Alexanna I personally am not knowledgeable to input on that (though it sounds probable). Hopefully someone who is knowledgeable can answer. : ) Thanks for the input.

Thanks again Bill for the input, I will return with results when available regarding whether there is voltage to the TV when it randomly shuts down. However, sometimes it could work for days so I'm not sure how soon it will be.

Also, can I just open the AC power supply when this happens and test the outgoing line for voltage?
If I test voltage on the fuses, where should I place my lead for the ground? Can I use any of the screws?

Thanks!

**PlainBill** · 05-24-2011, 02:08 PM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Originally posted by thisguy

Alexanna I personally am not knowledgeable to input on that (though it sounds probable). Hopefully someone who is knowledgeable can answer. : ) Thanks for the input.

Thanks again Bill for the input, I will return with results when available regarding whether there is voltage to the TV when it randomly shuts down. However, sometimes it could work for days so I'm not sure how soon it will be.

Also, can I just open the AC power supply when this happens and test the outgoing line for voltage?
If I test voltage on the fuses, where should I place my lead for the ground? Can I use any of the screws?

Thanks!

You can do it either way. If you decide to measure at the TV, measure from the left end of the 2A fuse to the screw directly below it.

PlainBill

**thisguy** · 05-25-2011, 03:04 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Well this time when I plugged in the AC adapter after it had been resting a couple days , the TV turned on and turned off immediately. It's done this before too. I did some tests with the multimeter. The voltage is 13.5 volts when not plugged into to the TV. When it's plugged into the TV its stays the same. When I try to turn on the TV, it drops to below 1 volt. If I unplug the line going to the TV and test the voltage on the AC adapter output, it is also 1 volt. If I unplug the AC adapter from the wall and plug it back in almost immediately, the voltage is 13.5 volts again. So it seems like when the TV is activated by the on/off switch (literally a switch in case you're wondering), something happens that causes the AC adapter to reduce below 1 volt. Perhaps some type of safety function. I tried to measure the volts when it actually occurs (when I activate the switch) to see if voltage spikes or anything. My multimeter did not show any spikes, it just went from 13.5 volts to 1 volt or less. I'm not sure if this means there is no spike in voltage or if it was so fast my multimeter did not register it.

If something is causing the AC adapter to shut off or go to less than 1 volt, it must be an over-volt? A short? The AC adapter output going to the tv has many wires, but there is nothing fancy. All the wires are soldered either to a ground or the 13V line on the AC adapter board.

**Th3_uN1Qu3** · 05-25-2011, 04:55 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Originally posted by thisguy

If something is causing the AC adapter to shut off or go to less than 1 volt, it must be an over-volt? A short? The AC adapter output going to the tv has many wires, but there is nothing fancy. All the wires are soldered either to a ground or the 13V line on the AC adapter board.

It's the power supply going into protection mode for whatever reason. Time to take apart that power brick and see what makes it tick.

**Village Electronics** · 05-25-2011, 07:57 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

"This made me suspect it was the bad AC adapter. I replaced it with a new one from Ebay. It seems brand new (OEM) and was from someone who sells lots of them. Opened it up and looks fine inside. But the problem persists. "

I find it hard to imagine that both power supplies could be defective in the same way without some problem in the TV causing that to happen. I would not suspect the TV to cause an intermittent operation of the 2 separate power supplies. It is not logical. In some TVs there is a mechanical switch that engages when a power supply is plugged into it. Does this have one of those? Have you examined the solder side of the plug? Can you post a picture of the plug?

**thisguy** · 05-27-2011, 03:08 PM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Sorry for the late reply.

Here are pics of the power socket on the TV and some pics of the AC adapter. It was difficult taking pictures of the AC adapter because the heat sink, so I apologize if they are of little use.

I don't think there is a mechanical switch, but I'm not expert.

Thanks!

Attached Files

**crtfool** · 05-27-2011, 03:18 PM

Re: Sharp Aquas LC-20B2UA random shut off issues.

You might be interested in this eBay listing - maybe you can get them to sell you 1 unit with much cheaper shipping - can't hurt to try.

http://cgi.ebay.com/Lot-4-Sharp-LC-2...item2a10f30cee

**PlainBill** · 05-27-2011, 06:34 PM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Originally posted by thisguy

Sorry for the late reply.

Here are pics of the power socket on the TV and some pics of the AC adapter. It was difficult taking pictures of the AC adapter because the heat sink, so I apologize if they are of little use.

I don't think there is a mechanical switch, but I'm not expert.

Thanks!

If you haven't already done so, check the point where the power jack is soldered to the terminal board in the TV. It seems like that could be a likely spot for bad solder joints.

PlainBill

**Village Electronics** · 05-28-2011, 08:09 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Originally posted by thisguy

Sorry for the late reply.

Here are pics of the power socket on the TV and some pics of the AC adapter. It was difficult taking pictures of the AC adapter because the heat sink, so I apologize if they are of little use.

I don't think there is a mechanical switch, but I'm not expert.

Thanks!

Note pictures 1 and 5. In picture 1 you can see the switch at the top of the plug. In picture 5, the drawing, you can see it as the little rectangular block at the top.

Below that plug the is a series of solder connections corresponding to the pinout of the drawing. Quite often those connections are bad. Users will often push the plugs hard to insure that the connection is made. Sometimes they even wiggly them to make it "work". It is a stress related problem. Check that the switch works cleanly with an ohm meter. That can be done by manual operation of the switch while you observe the change on the ohm meter.

**Village Electronics** · 05-28-2011, 08:12 AM

Re: Sharp Aquas LC-20B2UA random shut off issues.

Originally posted by thisguy

Sorry for the late reply.

Here are pics of the power socket on the TV and some pics of the AC adapter. It was difficult taking pictures of the AC adapter because the heat sink, so I apologize if they are of little use.

I don't think there is a mechanical switch, but I'm not expert.

Thanks!

Note also in picture 1, the two metal bars at the bottom of the socket. They may be the switches.

Sharp Aquas LC-20B2UA random shut off issues.

Sharp Aquas LC-20B2UA random shut off issues.

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