Dynex DX-L40-10A

[Mr Bill]

This tv is acting strange. When you first plug it in, led red (standby) you can hear static through the speakers like its on cable with no signal (snow). The snow sound does crackle. After a minute the sound gets less and less to the point you can barely hear it. If i unplug it and then plug it back in it restarts the snow sound. On the rare occasion i plug it in and i don't get the snow sound i can power it on with the keyboard but i get no screen. I shined my mag lite in several different spots but i can't find an image at all. When the tv does turn on if i try to turn it off with the keyboard it won't. I have to unplug it. I did get some voltage readings the few times i did get it to turn on.

5V and i'm getting 5.09
12V, i'm getting 11.75
16v, i'm getting 16.23
24v, i'm getting 24.45

The power supply is full of "peace" caps?? I've never heard of them and i can't find a datasheet for them. I did a quick esr checking in circuit and all the caps with the exception of the really big one and a smaller 4.7uf 450v, they are all in the .03 - .05 ohm range.

Scribd has the service manual. Doesn't give me much troubleshooting info. The flow charts all point to replace mainboard if the keyboard doesn't work and a no video. It does give schematics which to me is like reading greek at the moment. The BL on/off reading with the tv on is 2.877 and if i'm looking at the shematics right i think it needs to be in 3.3 range.

I am lost.

Here is the link for the service manual
http://www.scribd.com/doc/72513882/D...ual-DX-L40-10A

Would a shorted audio amp maybe cause the power supply to not fire up, protection mode? The led does not flash.

Thanks for any advice

[budm]

Re: Dynex DX-L40-10A

Did you try powering up without the power cable to the inverter board? The power supply seems to be working with all the voltages you see. It detects something and goes into shutdown?

[Mr Bill]

Re: Dynex DX-L40-10A

Did you try powering up without the power cable to the inverter board? The power supply seems to be working with all the voltages you see. It detects something and goes into shutdown?

I'm still getting the snow sound from the speakers. Have you ever heard of noise through the speakers when the tv is in standby?

[budm]

Re: Dynex DX-L40-10A

No, I wonder if you may have unstable power on the main board due to bad regulators?

[Mr Bill]

Re: Dynex DX-L40-10A

No, I wonder if you may have unstable power on the main board due to bad regulators?

I can check the voltage regulators tomorrow. I know there are several. I did do a quick once over on a couple and they seemed ok meaning 3.3v 5v ect. I'll have to list them out and pull the datasheets on each one to verify.

Thanks

[Mr Bill]

Re: Dynex DX-L40-10A

Bud,
I discovered something odd. When i get the snow sound from the speakers (led red/standby) i'm getting all the voltages i posted in post #1. Now after serveral on/off cycles with the power cord to get the no snow sound (led red/standby) i only get 4.76von the 5v pin, almost nothing on the 12, 16, 24 pins. I'm wondering if the power supply is send voltages to the main board that it shouldn't causing the mainboard to give me the snow sound.

[budm]

Re: Dynex DX-L40-10A

That does not make sense to me since the main board is the one that sends the PS_ON signal to the power supply board to turn on the 12, 16, and the 24vdc on. Is sounds like the main board is stuck in the ON mode even though it is supposed to be in standby mode.
We need to locate the PS_ON pin on the power supply to see what is going on there.

[Mr Bill]

Re: Dynex DX-L40-10A

I don't see a ps_on pin on the power supply. The pins going from the power supply to the main board are:

Gnd
Stb
5v_s
12v
br l
sw
5v_m

I did talk to the guy that owned the tv and he said before it started doing this the tv stopped picking up standard cable chanels. It would only show HD chanels. So it could possibly be the main board thats causing all this. I don't like throwing in the towel but it seems to me replacing the main board might be my only option. I did find one googling for $49.99 plus shipping.

[budm]

Re: Dynex DX-L40-10A

I think the STB (on_standby) or the SW is the PS_ON pin, measure them with the set off and with the set on.
I think these voltages are:
5v_s = 5Vdc standby, always on
5v_m = 5V main, switched on by the PS_ON.
12V = 12V main, switched on by the PS_ON.
br = backlights brightness control.
sw = may be PS_ON or Backlights inverter on control signal.

[retiredcaps]

Re: Dynex DX-L40-10A

I don't see a ps_on pin on the power supply. The pins going from the power supply to the main board are:

Stb

https://www.badcaps.net/forum/showpo...6&postcount=42

[Mr Bill]

Re: Dynex DX-L40-10A

I checked Stb and i'm getting .061 (led red) and 2.881 (led blue).

Sw i'm getting .015 led red and .025 led blue

Are you thinking its more the power supply instead of the main board?

[budm]

Re: Dynex DX-L40-10A

If the STB is at .061vwhen TV is off, then you should have no 12, 16, or 24v, but for you to have sound, then that mean the 12.16, 24 are on even though the TV is not being turn on. So next time you can hear the sound from the speakers when the TV is off is to look at the STB to see if it stays at 0.061v.

[Mr Bill]

Re: Dynex DX-L40-10A

If the STB is at .061vwhen TV is off, then you should have no 12, 16, or 24v, but for you to have sound, then that mean the 12.16, 24 are on even though the TV is not being turn on. So next time you can hear the sound from the speakers when the TV is off is to look at the STB to see if it stays at 0.061v.

When the tv is giving me the snow sound and the led is red (standby) stb pin is 2.881 and i am getting 12v, 16v, & 24v. I hooked up a cable line to see if i would get audio but it didn't. I did notice if the tv is plugged in and no snow is heard, led red, after sometime you will hear a pop from the speakers and then i have the snow sound everytime i plug it in. I then have to do the multiple on/offs with the power cord to get the snow sound to go away. When i do turn the tv on i can't turn it back off with the keypad or the remote.

[budm]

Re: Dynex DX-L40-10A

So some how the main board is sedning the command to turn on the power suppluy board even though it is supposed to be in standby mode, and since you also lost the control and unable to use the power swith or the remote, definitely the main board problem, but where? I need to download the service manual to study, we will have to start check the voltages of the regulators on the main board.
I cannot download the service manual, it wants to access my facebook account, so I deny it. Did you download it? Can you post the service manual or send it to me?

[Mr Bill]

Re: Dynex DX-L40-10A

I have the service manual but it won't let me post it. Its only 4.07 MB. Pm me your email address and i can send it that way.

[Mr Bill]

Re: Dynex DX-L40-10A

Bud,
I just plugged in the tv and the backlight actually turned in this time. I quickly went to check the voltage at the stb pin and it was 2.875. The screen was putting horizontal lines that were scrolling from top to bottom. I was getting the (snow) sound from the speakers. The keypad still wouldn't turn off. Should the stb pin be in the 3.3 range? There are 5 voltage regulators on the main board

SE8117TA
913-LF

From what i'm seeing on the datasheet i believe its an adjustable regulator. If it was a fixed there would be a 25, 33, ect at the end of the SE8117TA. I did hear a buzz from the transformer before the snow sound started again. Afer i unplugged it i plugged it back in and naturally the backlight wouldn't come back on for me to verify the noise.

[Mr Bill]

Re: Dynex DX-L40-10A

I checked the voltage regulators and according to the schematic i'm nowhere near what it should be. Do the resistors dictate the output voltage? Even the input voltage isn't high enough. Here are my results

(N1) Vin=5v Vout=?? I'm getting 3.184vin & 1.245v out. R19=180ohm (i'm getting 180.1) R20=300ohm (i'm getting 299.4)

(N3) Vin=5v Vout=3.3v, i'm getting 3.127v in & 1.263v out. R24=180ohm (i'm getting 179) R28=300ohm (i'm getting 298.9)

(N5) Vin=5v Vout=3.3v, i'm getting 2.863v in & 1.599v out. R29=180ohm (i'm getting 176.3) R33=300ohm (i'm getting 136.2)

(N6) Vin=5v Vout=2.5v, I'm getting 4.49v in & .756v out R31=100ohm (i'm getting 100.0) R32=100ohm (i'm getting 100.5 out)

(N8) Vin=?? Vout=1.25v, i'm getting 1.518v in & .532v out, R35=100ohm (i'm getting 59.2 ohm) R36=0 ohm (i'm getting 0.000ohm)

So R35 & R33 are reading low but i thought when a resistor fails the resistance goes up. I don't know where to look about the input voltages being low.

[budm]

Re: Dynex DX-L40-10A

Hi Bill,
I look at page 38, it shows you what you should get at Vo, it even gives you the formula to calculate the Vo value, please see the PDF.

[Mr Bill]

Re: Dynex DX-L40-10A

i just noticed my schematic didn't show the black text on it. I had to print it and scan because i couldn't pull the 1 particular page from the service manual. All the the voltages are low on the regulators.

[budm]

Re: Dynex DX-L40-10A

If the input are OK, but the out is out off the spec of the expected Vo base on the spec of the regulator, then I would say it is bad, not sure the spec of each regulators are, 5%, 10%