Polaroid P40LCD12

[ReeceyBurger123]

Re: Polaroid P40LCD12

I have seen D882 or the one next to it go leaky in the past, they don't fully short but go leaky. The part on them in Mur460ax. Remove them off the board and check for leakage current sounds like the failure if the Pcb around them is burning also.

[sweeney1987]

Re: Polaroid P40LCD12

Checked D893 ?

Yes and gettin .47 of a drop from both it and D901

On further inspection there is a slight burn mark arond leg of D882 (anode side)
It and D883 are giving me readings both directions indicating theyre shorted
will try swapping them out first, thanks

[ReeceyBurger123]

Re: Polaroid P40LCD12

Checked D893 ?

[sweeney1987]

Re: Polaroid P40LCD12

Did you ever find out if it was bad power board or main board, have same tv with exact same symptoms
would help greatly if you told me.

Searching there is a repair kit for these vestal psus, would that be fault?

[AFajitas]

Re: Polaroid P40LCD12

[nomoresonys]

Re: Polaroid P40LCD12

so many unsolved mysteries, I'm guessing the power supply swap fixed it?

[CapLeaker]

Re: Polaroid P40LCD12

Here is the schematic on the power supply.
On PL816 (a 28pin plug) measure the voltages of each pin and report back.

[Daveatfernie]

Re: Polaroid P40LCD12

That's what I was thinking with the LED not being illuminated.
Ill try the psu shorting again, if there's no joy I'll start by getting a new psu.
If I can get the psu to fire up I'll get a mainboard.

Thanks again for all your help.

[vinceroger69]

Re: Polaroid P40LCD12

ive had bad mainboards cause no power led dont rule it out. maybe budm or tom when there on maybe able to advise which pins to jump on the psu to check the other voltages etc.

[Daveatfernie]

Re: Polaroid P40LCD12

Tried forcing the psu in with the mainboard removed using a 470 ohm resistor but this was unable to start it either. (Connecting between 5v and power on input).
Still nothing other than 3.3 and 5v. The mainboard seems to be not trying to power the psu up.
The sw-switch input varies (sits at 5 when the mainboard is unplugged but raises to 7 with it connected). I'm unsure what this does and haven't traced it through the schematic yet.

I was thinking of trying to bastardise one of my other tv psus to power the board to see if it will fire it up. It's a shame there isn't a standard cable arrangement between psus. Until I can rule out the psu I'm at a loss to be honest as to where to have at.

I'll try the short between st_by and 5v tomorrow instead of the 470 ohm to see if there's any difference.

It also seems strange that if the mainboard is at fault(a psu on board the mainboard for example) that the indicator led isn't flashing (as the service manual indicates it should) there is no illumination at all on the power led.

[CapLeaker]

Re: Polaroid P40LCD12

Try to force the power supply on with a 1k Ohm resistor, if that doesn't work try just a jumper from 5V. 10k seems a bit too high.

[Daveatfernie]

Re: Polaroid P40LCD12

I've double checked all I can (electrolytics and such) but to no avail.

I'm surprised if it is the PSU board that the ST_BY would not be at 5V or similar though trying to get the power supply to fire up.

I'll buy a PSU board and then a logic board.

Hoping that the screen itself is in good nick after this

[Daveatfernie]

Re: Polaroid P40LCD12

I've tried to force the Sower supply to come up without any other board plugged in by connecting the ST_BY to 5V with a 10K.
I'm going to recheck the PSU board to see if I can see anything.

[nomoresonys]

Re: Polaroid P40LCD12

someone correct me if I'm wrong, seems if no back light after disconnect ps-on cable from g board to the a board, it's more likely a g board problem?

[Daveatfernie]

Re: Polaroid P40LCD12

Yeah, Nothing at all. With the any of the cables removed or not the PSU Never tries to power anything other than 5V and 3.3V.

I'm looking to buy a PSU and a mainboard but at the moment don't know which I'll need. Without testing that the PSU comes u pon it's own I can't tell.

Thanks

David

[nomoresonys]

Re: Polaroid P40LCD12

did you try unplugging the bl-on connector from power supply to main board, to see if back lights go on?

[Daveatfernie]

Re: Polaroid P40LCD12

Thanks I've cross posted onto this one as the other post was not resolved. That TV had a different fault as far as I can see as the PSU was powering up on it's own whereas mine stays in the standby mode. These are the schematics I was able to find also.

[CapLeaker]

Re: Polaroid P40LCD12

I have seen power supplies were there was no writings on top, but rather on the backside of the board.
Sure you can jumper the power supply on, to see if power supply puts out all voltages.
I would do some more checks on the mainboard first, before I powered up the main board like that.

[CapLeaker]

Re: Polaroid P40LCD12

Either next to the ribbon cable that goes from the power supply, or in the schematic diagram of the power supply... there should be a pinout indicating name and voltage.

here is an older thread you may want to read:
https://www.badcaps.net/forum/showthread.php?t=38728

schematic:

[Daveatfernie]

Re: Polaroid P40LCD12

On the output connector I can see:
SW_Switch output 7.425V
5VSTBY 4.8V
3.3VSTBY 3.3V

and no other voltages on the board conector.
As far as inputs I've found the ST_BY which I assume is the power supply on connector.
Everything else is an output from the PSU rather than an input from what I can see.
(Other than BL_ON, DIM, and A/D DIM).

Do you think I can 470 Ohm link ST_BY to 3.3V or 5 without the mainboard connected to see if it powers the board on its own?

Thanks again for your reply.