M421VT LED Screen Color Distortion

[dfang]

Re: M421VT LED Screen Color Distortion

It looks like the PS has now failed...The only dc voltage at main connector is the two 5.2vdc,,,no 12vdc,no 24vdc.....What the heck happened ? I only removed the shield on the main board..

[newtothis]

Re: M421VT LED Screen Color Distortion

It looks like the PS has now failed...The only dc voltage at main connector is the two 5.2vdc,,,no 12vdc,no 24vdc.....What the heck happened ? I only removed the shield on the main board..

Ok one will be 5v standby voltage, Is there a voltage legend near that connector?

Will be looking for something like PS_ON and we need to jump 5v Standby to PS_ON with a ~500ohm resistor. The other voltages will most likely come up and its actually the mainboard not sending the PS_ON signal.

Can try reinstalling the shield on the main and trying again... May be that the shield carries a ground.

Either way by the seems of it there is a fault or bad connection at the main IC... It is most likely going to be a BGA chipset as they are most prone to thermal failure.

[dfang]

Re: M421VT LED Screen Color Distortion

Ok one will be 5v standby voltage, Is there a voltage legend near that connector?

Will be looking for something like PS_ON and we need to jump 5v Standby to PS_ON with a ~500ohm resistor. The other voltages will most likely come up and its actually the mainboard not sending the PS_ON signal.

Can try reinstalling the shield on the main and trying again... May be that the shield carries a ground.

Either way by the seems of it there is a fault or bad connection at the main IC... It is most likely going to be a BGA chipset as they are most prone to thermal failure.

I reinstalled the heat shield,,no good result..Now trying to dig up a 500ohm resistor.. There is a voltage legend near the PS connector with PS_ON,,(see one of my last pic's)..Will jump one of the 5.2volt terminals with PS_ON..at the PS connector and man the fire extinguisher..

[newtothis]

Re: M421VT LED Screen Color Distortion

Remove the connector from the Main and use the resistor on the end of the connector, I have a feeling we will see all the voltages rise

[budm]

Re: M421VT LED Screen Color Distortion

It may have used the metal shield as the conductor path between two GND plane, you can see that the legs of shield are connected to big copper plane. Or you may have damaged the traces or through hole plating (for the top and the bottom side of the board copper traces) for the legs of the shield.

[newtothis]

Re: M421VT LED Screen Color Distortion

It may have used the metal shield as the conductor path between two GND plane, you can see that the legs of shield are connected to big copper plane. Or you may have damaged the traces or through hole plating (for the top and the bottom side of the board copper traces) for the legs of the shield.

Yeah noticed the planes hence suggested replacing the shield as it may carry the ground.

Got a feeling its going to be a BGA IC mindya causing the initial fault. Gonna be tricky to remedy without the tools

[budm]

Re: M421VT LED Screen Color Distortion

Or while removing the shield and flexed the board, what ever bad BGA connections it has it could have gone bad completely.

[newtothis]

Re: M421VT LED Screen Color Distortion

Or while removing the shield and flexed the board, what ever bad BGA connections it has it could have gone bad completely.

Also something I was thinking.

OP do you have a hot air rework station at all? I can try and guide you through reflowing the BGA if needed.

[dfang]

Re: M421VT LED Screen Color Distortion

Remove the connector from the Main and use the resistor on the end of the connector, I have a feeling we will see all the voltages rise

You mean disconnect the main connector and jump 5.2 vdc and PS_ON wires with a resistor at that connector ? Will a 765 ohm resistor work ? If not I will find something else..

[newtothis]

Re: M421VT LED Screen Color Distortion

Yes that will work fine, Plug the resistor into the end of the cable that goes to the PSU with it disconnected at main. I think the voltages will all come up, If they do I think me and budm are right in thinking bad BGA connections

[dfang]

Re: M421VT LED Screen Color Distortion

It may have used the metal shield as the conductor path between two GND plane, you can see that the legs of shield are connected to big copper plane. Or you may have damaged the traces or through hole plating (for the top and the bottom side of the board copper traces) for the legs of the shield.

You know Budm,,I think the copper traces or plating may have been damaged due to excessive heat trying to remove that shield and the shield indeed may play a ground roll on the board circuitry..I noticed around one of the holes for a shield leg kind of buggered up due to removal efforts..

[newtothis]

Re: M421VT LED Screen Color Distortion

Can you provide a picture of the damage, I am still thinking the BGA needs doing

[dfang]

Re: M421VT LED Screen Color Distortion

Can you provide a picture of the damage, I am still thinking the BGA needs doing

I need to remove shield again,,I'll provide pic when I get it removed..

[dfang]

Re: M421VT LED Screen Color Distortion

Ok,,got shield back off,,man I should put a zipper on this shield..

I don't see anything obvious but got to thinking,,,could have put too much heat on the board with heat gun and unsoldered some electronic parts...

[tom66]

Re: M421VT LED Screen Color Distortion

Looks fine to me - the soldermask (green protective ink layer) is damaged, but that is not critical to the function of the board. Copper is still intact.

[dfang]

Re: M421VT LED Screen Color Distortion

Yes that will work fine, Plug the resistor into the end of the cable that goes to the PSU with it disconnected at main. I think the voltages will all come up, If they do I think me and budm are right in thinking bad BGA connections

Ok,,with resistor jumped at main board connector,,PS Voltages are now:
ON-OFF=0vdc
DIM=3.28vdc
12v=2.52vdc
12v=2.53vdc
GND=0vdc
GND=0vdc
GND=0vdc
24v=0vdc
24v=0vdc
5.2v=5.14vdc
5.2v=5.14vdc
ACD=0vdc
I would like to have a known good main to try...

[newtothis]

Re: M421VT LED Screen Color Distortion

Ok,,with resistor jumped at main board connector,,PS Voltages are now:
ON-OFF=0vdc
DIM=3.28vdc
12v=2.52vdc
12v=2.53vdc
GND=0vdc
GND=0vdc
GND=0vdc
24v=0vdc
24v=0vdc
5.2v=5.14vdc
5.2v=5.14vdc
ACD=0vdc
I would like to have a known good main to try...

Can you confirm settings and what ground you are using for the tests please, Those are way off. Also check your meter battery

***EDIT*** Actually your 5v is correct so can't be meter or testing method, Has to be a PSU fault ***


So we now face a faulty PSU and Main! :/

Ok my view is that the BGA connections are bad causing your initial symptoms, This has a good chance at being sorted with a reflow.. So now onto troubleshooting the PSU...

Can you force the PSU on again and also use another resistor to the ON/OFF pin, This should boot the voltages for the Backlights

[dfang]

Re: M421VT LED Screen Color Distortion

Can you confirm settings and what ground you are using for the tests please, Those are way off. Also check your meter battery

***EDIT*** Actually your 5v is correct so can't be meter or testing method, Has to be a PSU fault ***


So we now face a faulty PSU and Main! :/

Ok my view is that the BGA connections are bad causing your initial symptoms, This has a good chance at being sorted with a reflow.. So now onto troubleshooting the PSU...

Can you force the PSU on again and also use another resistor to the ON/OFF pin, This should boot the voltages for the Backlights

Force PSU on again ? You mean jump with resistor at main board connector as before ? Use another resistor from where to ON/OFF pin ? STBY 5.2v ?

[newtothis]

Re: M421VT LED Screen Color Distortion

Onto the other 5v will do it.

So yes we are forcing the psu on and also forcing the backlight voltages on, This way everything "should" be on and we can see what voltages you are getting

[dfang]

Re: M421VT LED Screen Color Distortion

Onto the other 5v will do it.

So yes we are forcing the psu on and also forcing the backlight voltages on, This way everything "should" be on and we can see what voltages you are getting

Will attack it tomorrow,,I'm learning a lot...
Thanks for the help from you all...