Polaroid FLM323 Blue led, no video

[xyloeye]

I have to ask for some help on this one. While I realize Polaroid TVs are not first rate, I need to understand what's going on with it. I can't find a schematic but from my understanding, the only voltage from the PSU is 24v. I have 24v until I plug the main board in. Then the voltage goes to around 1v to the inverter and 16v at the main board. This happens whether the turn on voltage from the main board (4.9v) is used or if I turn it on with a resistor. There is no voltage on the inverter turn on pin.

I thought the main board was pulling down the PSU so I ordered a pullout board even though all the regulator voltages and caps on the board were good. No help.

Could the PSU be supplying 24v but with too little current? All the caps have normal ESR. They're all Nichicons! My only other clue is that the voltage on the main cap is around 180. I would think it should be higher in a supply with PFC. I know these PSUs are not particularly reliable but I have an emotional need to fix it now. It's ticking me off.

Any help would be very much appreciated.

[budm]

Re: Polaroid FLM323 Blue led, no video

You should try using the resistors on the the PS_ON pin and BL_ON PIN to see if the backlights will turn on with out having the board connected to the main board.
When force on the PS_ON pin, the 24V should be on steady. You can put dummy load on the 24V output pin, make the load to be about 2A (12 Ohms 100Watts resistor) to start with.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

OK, thanks. I'll give that a try.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

I checked the 24v output with two 1157's in series. The voltage varies between 22.6 & 23.7. The bulbs flicker a little also. Bad regulation on the supply?

[budm]

Re: Polaroid FLM323 Blue led, no video

"The voltage varies between 22.6 & 23.7", in your first post you have indicated that the 24V goes down to 1V when main board is connected. So the main board is not sending the PS_ON to turn on the 24V power supply.
Since you can force on the 24V, you should also then force on the inverter circuit by using the resistor between BL_ON and the 5VSTBY (no cable connection between the power supply and the main board), it may also need the resistor between DIM (BRT, ADJ) and 5VSTBY.
BTW, did the DC voltage on the main cap go up close to 370~400VDC when forced on?

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

That's the thing. There is 4.9v coming from the main board to the psu turn on pin. So I get about 1v to the inverter and 16v to the main board on the 24v pins. The only output from the psu (normally) is 24 volts, one connector to the main and another to the inverter. I think the only 5v standby supply comes from the main board and is regulated down from the 24 volts. So to turn on the inverter I think I have to use an external 5v supply.

I still have only 180v on the main cap when the psu is forced on.

I was also thinking the ripple might be high because of the voltage fluctuation. I'll check it with a scope asap.

Thanks for your quick replies.

[budm]

Re: Polaroid FLM323 Blue led, no video

OK, let me get this right, the PS_ON signal from the main board feeding the power supply board PS_ON pin is 4.9VDC.
"So I get about 1v to the inverter and 16 to the main board on the 24v pins" This 1V reading I do not understand. Do you mean the 24V output from the power supply to the inverter board is only 1V instead of 24V? The 24V also feed the main board?
I think we need to see the pictures.
The 5VSTBY power supply is used for running the main board, not the 24V. The 24V is more likely to be used for the audio power amplifers, most TV uses 12V for audio amplifiers.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

OK, let me get this right, the PS_ON signal from the main board feeding the power supply board PS_ON pin is 4.9VDC.

Correct, and the main board supplies it when plugged in.

"So I get about 1vdc to the inverter and 16v to the main board on the 24v pins" This 1V reading I do not understand. Do you mean the 24V output from the power supply to the inverter board is only 1V instead of 24V? The 24V also feed the main board?

When I force the psu on, I get close to 24v on both the connector to the inverter and on the connector to the main board (with the main board disconnected. If I plug in the main, the voltage to it goes to 16v and voltage to the inverter to 1v. From what I understand, the psu supplies only 24v, not 12 or 5 as usual.

I think we need to see the pictures.

I'll take a couple and upload them.

The 5VSTBY power supply is used for running the main board, not the 24V. The 24V is more likely to be used for the audio power amplifers, most TV uses 12V for audio amplifiers.

That's the weird thing. The main board receives only 24v. It's regulated to 5v and sent back to the ps-on pin. Main board supply is regulated down from the 24v on the board itself for its own supply as near as I can figure. Standby voltage in this thing is 24vdc!

[budm]

Re: Polaroid FLM323 Blue led, no video

That cannot be right at all.
Which one of the power supply do you have?
http://www.shopjimmy.com/catalogsear...olaroid+FLM323
Show us the pictures of the chassis, boards.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

This supply: Polaroid 846-240-H3CZZSH

In my pictures, the red circles are to inverter and are all 24vdc. The blue circles are the main board connectors. Red wires are all 24vdc and the one blue wire is the 5v ps-on wire.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

I can't seem to get a picture to upload. I'll keep working on it.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

Power supply. My circles didn't show up. Upper left connector goes to main. Lower left to inverter.

[budm]

Re: Polaroid FLM323 Blue led, no video

Too bad, shopjimmy shows the bottom side of the board with the heat transfer pad still in place so I cannot see the trace on the bottom.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

Here's the trace side.

[budm]

Re: Polaroid FLM323 Blue led, no video

OK, I look at the FLM3232 pictures, after looking at the main board and I can see two switching buck regulators on the main board which now make sense that this power supply only has two outputs: one is the standby 24V power supply, another one is the switched 24V (turn on by the PS_ON PIN1 with the blue wire) for the inverter board. This power supply is same one as used in the FLM3232 I had with bad LCD panel.
So when you jump the 24VSTBY to the PS_ON pin with 5K (not 1K because the stby is 24V not 5V), the switched 24V and the PFC cap should go up. The inverter on signal and the Dim signal flow through the big multi-pin (50-PIN Centronix) on the chassis that will connect to the inverter board.
http://s807.photobucket.com/user/bud...?sort=3&page=1
So you are 100% correct that this thing does use 24VDC STBY! The MAGMEET power supply for the other version of this same model uses 5VSTBY.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

Right. 24 vdc on all pins until I plug in the main board then everything goes low. That's why I replaced the main originally. I thought it was swamping the output from the psu. The ps-on & dim signals on the inverter come from the main board so I don't have a source on the psu to turn it on from just the supply. It's frustrating.

[budm]

Re: Polaroid FLM323 Blue led, no video

It is really hard to get to those control signal pins (BL_ON, DIM) on the main board. if the switched 24V for the inverter power supply does not work, it will not affect the BL_ON and the DIM signals to the inverter board, you can still look at the BL_ON signal on one of those 50-pin (I do not remember which one is the BL_ON and the Dim). if those signals are not present then you still have bad main board since those two signals are generated by the MCU and it does not care if the 24V for inverter is present or not.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

Yeah. I do have 4.9v going to the inverter bl-on coming through the funky
plug -in connector under the main board. I haven't checked the dim pin voltage. I got the replacement board from ShopJimmy so I assumed it was good. But it sure seems like it may be bad too.

[budm]

Re: Polaroid FLM323 Blue led, no video

If that is the case, then when you jumps PS_ON pin (the blue wire must not be connected) then jump 24vdc stby to the pin1 (blue wire) with 5K (or 4.7K), this should make the backlights and the PFC to come on, if the PFC still does not come on, then you do have power supply problem. Notes: I am not 100% sure if the the dimming signal is not present the backlights will come on or not.

[xyloeye]

Re: Polaroid FLM323 Blue led, no video

I might not be understanding some terminology. By PFC you mean power factor correction, right? How would I know if it's working? And do you mean to jump 24v through a 5K to the back light on pin?