coby 40" lcd TFT V4028 no sound

[jsog]

Re: coby 40" lcd TFT V4028 no sound

Ive capped everything but the 24v inverter supply there is no ripple, no bulging, no reason to suspect that and im almost out of 1000 uf caps.

How are you measuring ripple? Lots of caps fail without bulging. Have you replaced the small electrolytics?

[PlainBill]

Re: coby 40" lcd TFT V4028 no sound

The sound is fine. There was a connector unplugged from the power supply marked a24 or something like that.... apparently the audio runs on 24v because thats what it meters out at and thats the connector that was off..

Im having a hard time wrapping my mind around how the power supply "knows" when to turn the 12 and 24v on and off. frickin weired.

i will take and post some better pics of the power supply and connector designations...

Whew, I've been over this A LOT. Now it's your turn to be on the receiving end.

The power supply is actually two supplies in one. A standby supply (typically 5 volts) is always on when the TV is plugged in. That powers a standby section of the main processor. When the standby processor senses the power button being pushed, it sends a control line high, which turns on the main supply which supplies 12V, 24V, etc.

PlainBill

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

thasts what i dont get. Im not seeing any line switching between the set bieng on and the set bieng off.

iirc "pson" is always at like 4.2v and "5vstby" is always at 5v no matter wether the set is working or not working on or off. Perhaps one of those is pulled low for a split second and im just not catching it with my meter. COuld always scope it to me sure(theres a whole other can of worms he he its been a long time since ive used my scope...)

to make mattters worse, i have now lost my 24volts for interters. 24v for audio still there 12v still there.

here are a ton of ps pics for your viewing pleasure.

My whole deal with this has been how to figure out is the mainboard is falsely commanding the 12v and 24v sections on when first plugged in when they should be standing by, or if the ps itself is to blame and coming up on its own, where to go from there. im not going to find this ps on ebay or shopjimmy.

Its driving me nuts.

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

How are you measuring ripple? Lots of caps fail without bulging. Have you replaced the small electrolytics?

ac... between ground and the positive side of the caps(at power connector) with my meter.

i guess i could always break out the old scope to make sure but i have new issues to chase now

[b700029]

Re: coby 40" lcd TFT V4028 no sound

The power supply is actually two supplies in one. A standby supply (typically 5 volts) is always on when the TV is plugged in. That powers a standby section of the main processor. When the standby processor senses the power button being pushed, it sends a control line high, which turns on the main supply which supplies 12V, 24V, etc.

From the pictures this PSU is slightly different, SMPS is always working. 5V and 12V are controlled through MOSFETs, 5VSB is just connected to the 5V rectifier output. The MOSFETs seem to be connected (if blue wire in attached picture is a jumper or similar) so when 12V is switched on, 5V is switched on in that order. PSON is not an input but more like "power good" signal, it seems to be connected to ground through a transistor. The base of this transistor is connected to the control signal for the MOSFETs via some circuitry involving the optocouplers.

to make mattters worse, i have now lost my 24volts for interters. 24v for audio still there 12v still there.

That is very strange, A24 is taken from the inverter supply through something probably like a resistor/coil (cannot see in the pictures). I don't see any obvious way in which 24V supply is controlled. (probably on the primary side?)

If you provide a larger picture of the area in the blue rectangle, I can help figure out more about this circuit.

[PlainBill]

Re: coby 40" lcd TFT V4028 no sound

From the pictures this PSU is slightly different, SMPS is always working. 5V and 12V are controlled through MOSFETs, 5VSB is just connected to the 5V rectifier output. The MOSFETs seem to be connected (if blue wire in attached picture is a jumper or similar) so when 12V is switched on, 5V is switched on in that order. PSON is not an input but more like "power good" signal, it seems to be connected to ground through a transistor. The base of this transistor is connected to the control signal for the MOSFETs via some circuitry involving the optocouplers.

That is very strange, A24 is taken from the inverter supply through something probably like a resistor/coil (cannot see in the pictures). I don't see any obvious way in which 24V supply is controlled. (probably on the primary side?)

If you provide a larger picture of the area in the blue rectangle, I can help figure out more about this circuit.

You've done a masterful analysis and a superb job of identifying and labeling the picture, but you are wrong about PSON. It is clearly an input. It feeds the base of a transistor (identifier not legible) whose emitter is grounded and collector goes to an optoisolator, U4. In the top view, note the orientation of U4 and U5 - both are mounted with the emitter connected to the cold ground side of the power supply.

PlainBill

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

well i have confirmed that the rest of the set is good,. the power supply is definately my problem.

i dug around my junk tvs, didnt find any ps exact but found one in a old proscan(32lb30qd)with a simular pinout.(heres one like it, several of these on feebay)
http://cgi.ebay.com/Proscan-Megmeet-...item27bd1c7a3b

i carefully marked my terminals, repinned the connectors to match.

when the tv is plugged in it goes into standby everytime like it should, powers up and down as commanded fine. Im going to let it run awhile and recheck but yeah im thinking i definately have a bum supply.

Now to do some detective work and find out wtf is up with it. or leave this rigged krap mess in there lol..

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

From the pictures this PSU is slightly different, SMPS is always working. 5V and 12V are controlled through MOSFETs, 5VSB is just connected to the 5V rectifier output. The MOSFETs seem to be connected (if blue wire in attached picture is a jumper or similar) so when 12V is switched on, 5V is switched on in that order. PSON is not an input but more like "power good" signal, it seems to be connected to ground through a transistor. The base of this transistor is connected to the control signal for the MOSFETs via some circuitry involving the optocouplers.

That is very strange, A24 is taken from the inverter supply through something probably like a resistor/coil (cannot see in the pictures). I don't see any obvious way in which 24V supply is controlled. (probably on the primary side?)

If you provide a larger picture of the area in the blue rectangle, I can help figure out more about this circuit.

i can take any pics you want. THANK YOU to you and bill you are really shining some light at some stuff i wouldnt be able to figure out on my own.

Id really like to fix this ps if i can, im not going to learn anything if i just replace it.

the "blue wire" you added- there is in face a jumper ont he other side of the board you were correct there.

i have been discharging the filter caps every time is pull this ps, it was after the last time of doing that that the 12 doesent work, so mabye i took something else out. Im doing it old school just shorting em and letting em pop a little. Nothing worse than getting bit by a cap or by an anode on a crt monitor... i know that hurts from experience..

[jsog]

Re: coby 40" lcd TFT V4028 no sound

Are the light blue caps the new ones? What brand and series are they? (The thinking being that they look like normal ESR, general purpose, 85 degree types, and as you replace more, the problem gets worse. Whether a ripple problem would show on a meter depends on the meter.)

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

yeah they are my cheapie arcade monitor caps, xicon brand. i am out of the good ones at the moment(BEEN BOUNCING AROUND FROM THE LOW ESR XICONS, PANSSONICS, SAMXONS, whatever lol im not really a brand nazi if it works it works.

WIth these i figured theyd be good enough to test with, have gotten away with it in the past mabye this set is where my luck ends.

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

Well i mightve been good if i wasnt such an idiot.

I did go ahead and check the 5v and 12v fets, not shorted checking good.

in the 24v primary side, i found arc damage to a polypropelene capacitor
(c38). this trace ends up all over the place so who knows what all i fried.

For now, shes going to rock this new proscan power supply. These ps issues seem to be beyond my skill level unfortunately. If any of you guys want this to tinker with yourself let me know. heres more pics, having a hard time getting the camera closer. My wife has a canon 50d but i have to steal it sometime shes not around and i know i can get great macro shots with that.

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

its been 10 days, tv has been used every day for about an hour in the morning. and several hours every evening.

while i would not reccomend this hack to everybody as you do have to pay particular attention when you repin and swap out terminals, and who knows if this ps s rated anywhere near the same watts as the original, but in my case this has worked out great!

[alej3996]

coby 40" lcd TFT V4028

Hi guys, i have another problem, i buyed 6 month ago this LCD TV and a over tension on AC line broke my mainboard, now i buy a new main board but is not the same, my original main board have a serial number: 002-fv40-2810-00r and the new, have: 002-fv40-2812-00r, in the service center an engineer told me that fits for my Tv, but isnt true, because on the TCON conector the first have 36 pin, the second have 40 pin, when a put on my tv, all working good, but the image is distorted, only see the dark sides, now my question is, have any body a schematic of this TV?, is quiet hard to my find it on Google. Could any body help me pl?. Thanks.

[alej3996]

Re: coby 40" lcd TFT V4028 no sound

Hi guys, i have another problem, i buyed 6 month ago this LCD TV and a over tension on AC line broke my mainboard, now i buy a new main board but is not the same, my original main board have a serial number: 002-fv40-2810-00r and the new, have: 002-fv40-2812-00r, in the service center an engineer told me that fits for my Tv, but isnt true, because on the TCON conector the first have 36 pin, the second have 40 pin, when a put on my tv, all working good, but the image is distorted, only see the dark sides, now my question is, have any body a schematic of this TV?, is quiet hard to my find it on Google. Could any body help me pl?. Thanks.

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

you need to get the proper board and you wont fine one.

these are fantastic tvs for cheap but theres just not parts or info available for them.

My power supply retrofit is still working great, btw.

[cadillacman]

Re: coby 40" lcd TFT V4028 no sound

Just to followup its been almost a year and this set is still working great with the retrofit. I use the set daily for about two hours a night.