Emerson LC401EM2F Flashes "Digital Television" then goes black

[kf4lne]

I have an Emerson lc401em2f that will not fully power on. When the power button is pressed, the red light flashes for about a second or so then the screen illuminates with the usual glow indicating the inverter and lamps powered up, flashes something very quickly in the bottom RH corner of the screen then the lamps go out and it appears the device shuts down. I was able to make a video recording of the sequence and found the words that flash in the corner are "DIGITAL TELEVISION". The power supply board was replaced, and as best as I can tell all of the voltages that are labeled on the board are testing within about 10%-ish of the marking. I saw other threads about this model of TV ad have followed some of the applicable troubleshooting. The power supply board has been replaced with a known working board. Does anyone have any suggestions of what to look for in this TV that would cause it to behave this way?

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

When it shuts down - does the backlight stay on? If you press the SOURCE or INPUT button while running, see if you can get it to change the source it uses (e.g. changing the text to "HDMI") - this will prove if the main board stays running but the inverter shuts down.

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

No, the device pretty much powers off. No backlight, no power indicator, no relay clicks or anything else. The sequence is like this:

Press Power> Relays click, power indicator flashes then solid, backlight comes on immediately followed by the words flashing in the corner, backlights and power indicator immediately go off and at the same time the relays click again. All of this happens in about 5 seconds.

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

Will the TV turn on again and repeat the sequence if you press the power button or does it "lock out"?

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

It will turn back on as soon as the power button is pressed and go through the cycle again. I can do it all day with the same result.

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

OK. I suspect the inverter board or the main board. You have a multimeter? Can you post a picture of the inverter board? It's the board that the red and black multi-wire connector plugs into (not the power supply.)

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

Here is the inverter board. Quality may be lower than the others, had to take the pic with a HTC phone.

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

Are there any labels near that connector, either on the power supply or on the inverter?

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

There are labels on each end of the cable. On the PS board they are as follows:

Top>Bottom

PWM-SEL
BL-ADJ
BL-SW
ERROR
GND (5 pins)
24V (5 pins)

On the inverter board, the connector is marked CON1,
Pins 1-5 VIN
6-10 GND
11 ERR_OUT
12 ENA
13 DIM
14 EX_DIM

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

OK, this inverter has an error signal. That is a rare feature, but it could be that the inverter detects a fault, which then causes the main board to shut everything down.

Can you set the TV up as normal, and check a few things:

- one of the VIN pins
- the ERROR_OUT pin
- the ENA pin

To check them: Set your meter to the 200V scale; don't worry, the maximum measured will be about 24V, we just need to use a scale which will work. Then, place the black probe in the chassis of the TV. Probe the pin of interest with the red probe and then turn the TV on normally. Watch for any changes. I am expecting the ERROR_OUT to quickly come on, but then go off after a couple of seconds as the power supply shuts down. I'm also expecting you'll see VIN at around 24V (+/-1V) for a couple of seconds.

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

VIN is 23.3
ERROR is 0.8 then quickly drops to 0
ENA 2.5

VIN and ENA remain the same after the system appears to power off. Pressing the power button again causes those voltages to momentarily drop then come back up, almost as if pressing the power button is causing a "reset" effect.

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

Did you get the TV as faulty or have you owned it since new/used? Since the voltages are staying up you -should- be able to select a source, or connect an antenna and listen to digital TV. I am pretty sure that the problem is the inverter if it shuts down with good 24V and enable pin being high.

Try this test. Test the ohms between each pair I've drawn. Use 20k ohm range, TV must be unplugged. Test the other transformer too - the one on the lower side. All readings should be nearly the same, within +/-3% of each other.

The photo isn't clear enough to see if there are any fuses on the board (there are almost certainly some), so if you get the chance, please take a clearer shot with a better camera. I had a TV which would briefly flash the backlight and it was due to a blown fuse, it was detecting a fault with half the bulbs because there is one fuse for each set.

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

All readings were between .610 to .614 ohms. I got this TV in this condition. The power supply board had been previously replaced and I have both the old and new power supplies. There are 2 fuses on the inverter board, both test good. No blown caps and no obviously damaged components or discoloration from heat. Also, the inverter output runs about 700v for a couple of seconds during the time the screen illuminates, this is regardless of weather or not I have the lamps connected. Same problem happens on either power supply.

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

You should avoid testing the inverter outputs some multimeters can be damaged by the high frequency AC (worse than the high voltage.) When the TV starts approx twice the operating voltage is applied to strike the bulb and make it light. But you are saying that you get continuous voltage, and the CCFLs go out before it dies?

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

Yeah, the inverter voltage jumps up to about 700v, it may reduce but the TV dies so fast it probably doesn't have time to register. As far as my meter being damaged, I think it will be OK. Its pretty well suited for use with high powered transmitters and other high voltage high frequency measurements. I work primarily in radio communications and information technology, but TV repair is a new experience for me. I am not thinking I will be liking this.

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

Hmm... you wouldn't happen to have a scope, though?

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

I have a 40Mhz scope.

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

That's quite helpful. You can try seeing if there's a brief spike on the ERR OUT pin. It could be very brief. If there is, then the inverter is shutting down because it detects a fault.

[kf4lne]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

This is the first opportunity I have had to get back and update this post. There is a spike on the error pin, but its just a quick spike. I didn't need a scope to measure that, just a meter that responds faster. I can't really give you any details about the spike other than its very quick and happens before the initial problem happens, so its probably more related to the device initially powering on rather than the device failure.

[tom66]

Re: Emerson LC401EM2F Flashes "Digital Television" then goes black

OK then, I would still suspect the inverter, as it may have a failure not signalled by the error pin.