Polaroid FLM-373B Power LED but no picture, already tried replacing caps

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

It looks like that is the correct data sheet for this power supply, that is an impressive find. I still can't determine where PS_ON is though, I don't see it labeled anywhere on the board. I've attached a couple pictures of where the main board plugs in, hopefully that will be helpful. Sorry for the quality of the pictures, I lost my camera charger when I moved so I had to use my phone.

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

PS_ON is sometimes marked ON/OFF or STB (as it looks like in this case.)

Use your multimeter to check if PSON is staying on when trying to turn the TV on.

[selldoor]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Thought it might be Pin3 Connector 105- see attachment
but that differs from your picture ? Hmmm! Perhaps not the correct data sheet?

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Ok, this is interesting... STB (PS ON) is staying at a constant 5 volts even after my power board output voltages drop to zero. I'm thinking this maybe points to the power board being at fault?

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Ok, this is interesting... STB (PS ON) is staying at a constant 5 volts even after my power board output voltages drop to zero. I'm thinking this maybe points to the power board being at fault?

Hmm. Yes, that does seem likely. I should have asked you to check this; it slipped my mind but I recently came across an LG Plasma where I thought the problem was the power supply but it was the main board turning it off. In this case, it looks like it is genuinely the power board at fault.

Can you unplug the main board from the PSU and connect the 3.3k resistor from 5V standby to STB, and see if the supply fires up?

[PlainBill]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

If that doesn't work, check the voltage at the STB pin WITHOUT the resistor to 5V standby. If it is still at 5 volts, try pulling it to ground. I have encountered power supplies that are turned on by pulling the SBY input low.

PlainBill

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

If that doesn't work, check the voltage at the STB pin WITHOUT the resistor to 5V standby. If it is still at 5 volts, try pulling it to ground. I have encountered power supplies that are turned on by pulling the SBY input low.

PlainBill

The datasheet says active high but it certainly could be active low. Wouldn't be the first time a dodgy datasheet has been encountered.

[PlainBill]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

The datasheet says active high but it certainly could be active low. Wouldn't be the first time a dodgy datasheet has been encountered.

That's the point. LOGICALLY a standby input would turn off the main supply (standby) when the input was high, and a PS_ON input will turn on the main supply when it is high. But there is no consistency.

PlainBill

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Ok, tried a few things. With everything unplugged and a resistor between 5VSB and STB, the power supply outputs all the correct voltages. With the inverter board plugged in and the resistor connected, the voltages are also all correct. When the main board is connected, however, the voltages all drop to zero.

With everything plugged in, connecting the resistor between GND and STB has no effect. I'm kind of afraid of running a direct jumper wire between GND and STB because I don't want to blow everything up, but if you guys think I should try that to see what happens I will.

[PlainBill]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

No need to jumper the STB input to Gnd. Since the resistor to 5V standby turns the power supply on, the main board is overloading the power supply, causing it to shut down. Now you have the enviable task of finding out which component on the main board is at fault.

PlainBill

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Now you have the enviable task of finding out which component on the main board is at fault.

PlainBill

Well this should be a great time. There's a replacement main board on ebay for $80 that I might just grab, I feel like I'm not gonna be able to figure this one out. I've determined that when I unplug the wire I circled, the TV mostly powers up (backlight comes on, but nothing appears on screen), so something powered by that is causing the problem. I'm thinking this is still gonna be quite difficult though.

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

http://www.youtube.com/watch?v=XhqwC...el_video_title

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

http://www.youtube.com/watch?v=XhqwC...el_video_title

Ha, that is brilliant. I'll give that a shot, thanks for the link.

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Thought maybe you guys who have helped me would like an update on this... The "freezer spray" test didn't help figure anything out, but by hooking up a 9 volt battery to the pin that was causing problems, I was able to narrow the problem down to a tiny little area by checking voltages across the series of capacitors on the board (one had voltage across it, then the traces went through a few tiny little surface mount things, and the one after that read 0v).

I realized that even if I could figure out specifically which component was causing the problem, I don't have the skill to solder a component that tiny, and decided to just order a new main board from ShopJimmy for $65 when I get my next paycheck.