Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

[SurrealMustard]

New findings

On this TV PSU, each string has its own control ic, etc. IC1301, IC1201 and IC1101. Each has its own circuitry to control one string each. Now you have to find out which circuit isn't working. I am guessing the one with IC1201 since it is the middle one, but you have to verify that.
What part numbers does IC1201, Q1201 and Q1202 have? Check D1202 Q1201 and Q1202 for a short.

Q1202, Q1201, and D1202 are not shorted. The other two sets of corresponding ICs and diodes also look fine.

IC1201 has a part number of BD9488F. Q1201 and Q1202 are part number 18T10AGH.

[CapLeaker]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

Check IC1201 DC voltages. Chassis GND is your ground reference point. Download the spec sheet. It should tell you what the problem is. The chip has a few protection features built in. Nice thing is you can compare that IC to the other 2.

If you want you can try to "exchange" the back light string pins around. See if the problem moves.
With the PSU and the LED's unplugged, check the resistance between the 3 back light pins to GND on the PSU.
Check R1215 too, and maybe the voltages on the caps C1105, C1205 and C1305.

[budm]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

46ME313V_F7-4.pdf service manual. Chassis FL13.14?
Magnavox A3AQ0MPW-001 Power Supply for 46ME313V/F7
Part Number: A3AQ0MPW-001
Board Number(s): BA3AU0F0102 2, A3AQAMPW, A3AQ1MPW

http://www.shopjimmy.com/catalogsear...navox+46ME313V

Service manual.

[Diah]

Re: Tested lamps.

Well, I finally broke down and tore this thing apart. Turns out that there is some kind of issue with backlights not lighting up. The weird thing, however, is that after testing each lamp in the middle row individually with the multimeter, I found that they all light up and work. Does this mean that I've got a bad power supply?

lighting LED by testing not enough to judge they are good... reverse the multimeter probe and test each LED as DIODE Beep ton. you will find you have one or more shorted.

[SurrealMustard]

Power supply troubleshooting

Check IC1201 DC voltages. Chassis GND is your ground reference point. Download the spec sheet. It should tell you what the problem is. The chip has a few protection features built in. Nice thing is you can compare that IC to the other 2.

If you want you can try to "exchange" the back light string pins around. See if the problem moves.
With the PSU and the LED's unplugged, check the resistance between the 3 back light pins to GND on the PSU.
Check R1215 too, and maybe the voltages on the caps C1105, C1205 and C1305.

46ME313V_F7-4.pdf service manual. Chassis FL13.14?
Magnavox A3AQ0MPW-001 Power Supply for 46ME313V/F7
Part Number: A3AQ0MPW-001
Board Number(s): BA3AU0F0102 2, A3AQAMPW, A3AQ1MPW

http://www.shopjimmy.com/catalogsear...navox+46ME313V

Service manual.

Thanks for the tips. I'll do a bit more research into the power supply and see what can be done.

lighting LED by testing not enough to judge they are good... reverse the multimeter probe and test each LED as DIODE Beep ton. you will find you have one or more shorted.

I connected the multimeter to each Led in both directions, including the way that lights them up and the way that measures them. The measurement was always almost the same value and there was no sign of a short.

[RON_CET]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

The Voltage that should be present @ Protect 3 should be 3.3 volts once the backlight drive circuit turns on...and will constantly be there unless something @ the panel or the backlight drive circuit forces that Protect line low.If that voltage goes low (0 volts) most likely your having a led failure within the panel

[SurrealMustard]

(un)Happy ending

Swapped power supply, same issue. Either got a bad power supply or some kind of "stealth backlight failure." Either way, this thing is just beyond practical troubleshooting.

[Coldblackice]

Re: (un)Happy ending

Swapped power supply, same issue. Either got a bad power supply or some kind of "stealth backlight failure." Either way, this thing is just beyond practical troubleshooting.

By any chance were you ever able to determine what the problem was? I've come across a set with the same issue. Very frustrating, as it turns on fine, shows the logo across the screen just fine, and then shows a glimpse of HDMI1 source before immediately shutting off!

[nomoresonys]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

Interesting thread, it's a shame there was no resolution, another eternal mystery.

[budm]

Re: (un)Happy ending

By any chance were you ever able to determine what the problem was? I've come across a set with the same issue. Very frustrating, as it turns on fine, shows the logo across the screen just fine, and then shows a glimpse of HDMI1 source before immediately shutting off!

Did you do any Voltage testing? As you can see in post #17 showing LED strip not lit up. You need to at least do some Voltage checking.
You need to check those PROTECT 1, 2, especially PROTECT 3, and Voltage of each LED string Anode and the Cathode return pin.
As you can see, there are 3 LED driver circuits so you need to check all 3 of them.

[SurrealMustard]

Some closure...

By any chance were you ever able to determine what the problem was? I've come across a set with the same issue. Very frustrating, as it turns on fine, shows the logo across the screen just fine, and then shows a glimpse of HDMI1 source before immediately shutting off!

I never did. In retrospect, mirroring budm's thoughts, it was highly likely to be backlights though. I'd recommend a backlight tester to find out for sure, which is something that we've since invested in. For one crappy flatpanel, it might not be worth it. If you deal with any in the future though, it can be a useful purchase.

Interesting thread, it's a shame there was no resolution, another eternal mystery.

Indeed. Even I don't know the ultimate fate of the diagnosis.

[Coldblackice]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

Please forgive me for the necro! But I'm still trying to hack away at fixing this TV, though mine is a 50" (Magnavox 50ME313V).

Based on discussion and suggestions here, like the OP, I've narrowed it down to the LED strips, the TV shutting off after displaying the Magnavox logo and the "HDMI" source at the top right. At immediate TV startup, and whether the strips are plugged in or not (I've tested both ways), the voltages at all three LED drivers are about 55V.

After a moment, and assuming the strips are connected, 2 out of the 3 strips jump up to 85V or so. The middle strip, however, jumps up in voltage as if trying to reach the mid 80's V, but only seems to hit into the 60's, and then falls back down to 55V.

I then swapped the LED strip pins in the connector, connecting the middle LED strip to #1's place/driver, and #1 strip connected to #2's driver. The #1 strip works fine, reaching its ~85V, while #2 strip repeats the same behavior of trying to climb, reaches 65-67V, then falls back down to the baseline 55V (which the driver output is at even if the LED strips aren't connected). It's as if the TV tries to power up the #2 strip, detects something it doesn't like with it, then cuts it off.

So I disassembled the TV and as suggested here, I tested each LED with my multimeter in diode mode. Every LED lights fine, on the "bad" #2 strip, as well as the other strips. I've also reversed the multimeter leads as someone suggested here (unless I misunderstood that suggestion), and the voltage is the same across every LED: about .77V. I've also both ways in batches of 2-LEDs and 3-LEDs, for all three strips, wondering if maybe a difference might manifest on a larger sample size -- to no avail.

I'm at a loss of what could be wrong here. I have a bunch of good LED strips that I've parted out from other brand/manufacturer TVs, and I was hoping to be able to solder in good LEDs for any bad ones, not wanting to have to buy a new strip because 1.) this is a friend's throwaway TV, and I'm hoping to fix it with what I have, if possible, and 2.) the learning experience of finding/isolating/fixing a specific problem point.

Any possible ideas what might be the issue here (with LED strip #2)?

[thuexedanang]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

.

[neilc6]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

Testing each LED in diode mode with a multimeter doesn't put out enough current to stress it. Newer LED testers can pump out a couple hundred mA which matches what the power supply puts out. If the voltage indicated on an led tester doesn't match the other strips or if a single led has a delayed turn on, then I would replace that strip.

[Coldblackice]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

Testing each LED in diode mode with a multimeter doesn't put out enough current to stress it. Newer LED testers can pump out a couple hundred mA which matches what the power supply puts out. If the voltage indicated on an led tester doesn't match the other strips or if a single led has a delayed turn on, then I would replace that strip.

I'm just seeing this response now, but I did some further testing last night, and it would seem that you've hit the nail on the head --

Here are pics of the TV's LEDs: https://imgur.com/a/LhybiuT





As you can see in the pictures, each strip is divided into halves, the left half with 12 LEDs, the right half with 11, joined in the middle by a JST connector. Not yet knowing what neilc6 mentioned above, I decided to at least try isolating which strip-half was causing the issue. So I unplugged the strip-halves of the apparent bad strip, #2, and a good strip, #1. I then cross-wired the halves between each other, so #2 first half connects to #1's second half, and vice versa. After turning the TV and trying both directions, it's the left-side half of strip #2 that seems to be causing the problem, as it never lights at all. The right half of strip #2 lights fine when connected to #1's left half.

But my multimeter was still lighting each individual LED just fine, and the reverse-polarity voltages + resistances were all the same, frustratingly. I took a 60FPS video with my cellphone while the TV powered up, and I could see that the middle strip was lighting up entirely as soon as the TV powered on, but only for a blip, before going dark while the other strips lit up fully. This confused me even more, as I could see that all of the middle strips LEDs were lighting up during that pulse.

For this next test, I'm guessing it wasn't the wisest thing to do for the health of the electronics, but while holding the power strip the TV was plugged in to, I turned the TV off, then turned it back on and noticed that all of the LEDs pulsed for just a microsecond. This is before they would normally light up. Before they lit up fully, I shut the power off, waited a sec, then turned it back on. I noticed the pulse blip in the LEDs again. I did this multiple times back to back, and I noticed that on the middle strip's left-half, the first two LEDs on it weren't lighting as strong as every other LED on all strips. Wondering if it was a fluke, I pulsed a handful of times, and those two LEDs were definitely dimmer than all the others, and I believe at one point they may have even stopped lighting altogether -- I'm guessing I may have finished them off with this stupidity. I was frustrated and nearly done with this headache at that point, so I thought why not.

Looking closer at those two LEDs, I noticed something curious -- the strip's PCB is lifted away from its backing slightly. I pushed it back down, it stuck for a second, and then lifted back up, the adhesive not sticking enough to keep it down. Looking at the plate that each strip was stuck to, I see that they're each labeled "LED heatsink". My guess is that this could have something to do with the issue -- perhaps the heat caused the part of strip these two LEDs were on to unstick from the heatsink, and thus, now not have any protection against heat, and so they overheated and aged themselves faster relative to all the others. Not sure if this is the "chicken" or the "egg", however -- if they unstuck and then the lack of heatsink caused that to nearly burn them out, or if they shorted or something, and then that caused it to unstick. Or if it's just coincidence altogether.

Anyways, apologies for the long-winded detail, just thought I'd write it in case anyone else comes across this, as others' tips and troubleshooting above have helped me.

neilc6 -- if my multimeter (87V) can't sufficiently put out enough current to do the job, is there something else I can do to test/confirm besides buying an LED tester? Even though it seems to be those two LEDs on the #2's left strip, it'd still be nice to be able to definitively determine that they're the issue, and also see via measurement how they differ from the others, for my own understanding/learning.

And then finally, as I have other LED strips I've parted out from various people's TV throwaways (this TV being someone's throwaway, as well), I was hoping to be able to do any repairs myself without buying replacement parts. Would I be able to solder in LEDs from the good LED strips to replace any bad ones here? The other LED strips are from cracked screen TVs, so I assume they're all good (but will still test as soon as I learn how to see the difference in measurement).

Thanks guys!

[neilc6]

Re: Magnavox 46ME313V/F7 LCD shuts off immediately after displaying splash screen

I have noticed LEDs sitting on a cavity or where double sided tape has become unstuck are points of failure due to lack of heatsinking. Replacing LEDs themselves requires a reflow station or hot plate since they are surface mount parts. The main LED I encounter is 3V LG 3528 large pad anode positive (search Aliexpress). Samsungs typically are large pad cathode but I typically do full strip replacements. With the 3 black dots, I would suspect they are 3V LG compatible. May be easier to find strips on ebay.

After repair, you need to turn down the backlight level. For RCA's, menu-1-1-4-7 in the service menu under panel settings. Default may be 80 and I turn it down to about 55.