Polaroid FLM-3232 Dead 24V Rail

**budm** · 04-03-2013, 01:51 PM

Re: Polaroid FLM-3232 Dead 24V Rail

The current sensing (CS) pin is connected to the Low Ohm Source resistor (<1 Ohm resistor)? That can be the reason it is showing short. If you look at page 6 of the spec sheet, you will see example circuit and it is connected to 0.31 Ohms Source resistor.
Can you also post 1/4 section pictures of the board, top side and bottom side?

**martyparish** · 04-03-2013, 03:27 PM

Re: Polaroid FLM-3232 Dead 24V Rail

Hi Bud thanks for jumping in! Yes, I was looking at that schematic and thinking the same as you stated. Maybe it wasn't a dead short but just low reading after all. I'll check that again to be sure.

Let me know if these pics are satisfactory. I labeled them b_1 - b_4 and f_1 - f_4.

I inverted the front image so that f_1 and b_1 are the same quadrant.

Thanks again!

Attached Files

**martyparish** · 04-05-2013, 11:39 AM

Re: Polaroid FLM-3232 Dead 24V Rail

Update: I went ahead and ordered the three caps near the 24V rail. Those are Lelon brand and figured it was worth a shot for a few bucks. All the rest of the caps are Rubycon and Nichicon.

Will post back after they arrive. (I've asked a mod to relocate this thread to the TV forum)

**Th3_uN1Qu3** · 04-05-2013, 02:01 PM

Re: Polaroid FLM-3232 Dead 24V Rail

If it's got PFC and you only get 170v on the main cap, then you have to fix the PFC circuit. You should be getting around 380-400 volts when the PFC is operating.

**martyparish** · 04-05-2013, 02:56 PM

Re: Polaroid FLM-3232 Dead 24V Rail

Thanks for the input Th3_uN1Qu3. I thought the voltage was incorrect and that it should be around 400 at some point. I will see what else I can find out when I open it back up.

**budm** · 04-05-2013, 06:05 PM

Re: Polaroid FLM-3232 Dead 24V Rail

Since the L6561D which is for the PFC is not working, with board not connected to the power and the Main cap is discharged (check the voltage on the main cap) please take the resistance reading on all the pins of the L6561D against the Ground pin (pin 6) and report the reading. I have a feeling you have bad PFC IC.

Attached Files

L6561 PFC.pdf (176.8 KB, 38 views)

**martyparish** · 04-08-2013, 08:59 AM

Re: Polaroid FLM-3232 Dead 24V Rail

Sorry for the delay guys. I just got my parts in and now have the TV opened back up.

Bud, here are the results of the PFC resistance, all referenced to pin 6 ground:

1: OL
2: OL
3: OL
4: 0.7 ohm
5: OL

7: OL
8: 50 ohm

I'm going to install the caps now just for kicks but not expecting any miracles...

Thanks again fellas!

**budm** · 04-08-2013, 12:29 PM

Re: Polaroid FLM-3232 Dead 24V Rail

Pin 8 (VCC) does not look right at 50 Ohms, the Zener diode inside the IC may be bad. I would replace the IC.

**martyparish** · 04-08-2013, 12:45 PM

Re: Polaroid FLM-3232 Dead 24V Rail

Thanks Bud. I will order it asap.

What's weird is, I replaced the three 1000uf 35V caps and tried the set but now my 24V stand by is way low and fluctuating! I've triple checked the cap install and all looks fine.

Originally, I had a solid 24V and the PS_ON would go to 5V when I hit power but now 24V hovers from 2-5V~. What the heck???

**budm** · 04-08-2013, 12:50 PM

Re: Polaroid FLM-3232 Dead 24V Rail

The 12v/24 power supply section need 380VDC (provided by the PFC Voltage booster) for it to run correctly, right now it is only getting 170VDC feeding it.

**martyparish** · 05-03-2013, 05:10 AM

Re: Polaroid FLM-3232 Dead 24V Rail

I have replaced the PFC IC and still only getting 170VDC at the large cap

Sorry it took so long to update you guys, it's been hectic around here.

I'm going to have another look at this tv today and see if I can find anything else.

If it is not the IC, what would be the next component to look at?

I want to thank you guys in advance, the help is always appreciated! I've fixed quite a few units now thanks to all the information provided here! The latest was my 22" monitor that wouldn't turn on in the morning. (bad caps of course!)

**budm** · 05-03-2013, 08:52 AM

Re: Polaroid FLM-3232 Dead 24V Rail

Check the voltage on the VCC pin8 of the PFC IC. Also check and see if you still get 50 Ohms reading on the VCC pin8.

**martyparish** · 05-03-2013, 10:15 AM

Re: Polaroid FLM-3232 Dead 24V Rail

It reads 50 ohms between pin 6(gnd) and pin 8.

I tested voltage on pin 8(Vcc) and it begins around 4.8V and slowly drops out.

I used pin 6 as the ground ref, is that okay?

Thanks again, much appreciated.

**Th3_uN1Qu3** · 05-03-2013, 10:22 AM

Re: Polaroid FLM-3232 Dead 24V Rail

Yes, the way you measured is correct. What i see is that you're not getting enough voltage on the Vcc pin to power up the PFC chip. That's due to the 50 ohm resistance you get from Vcc to GND, which you shouldn't be seeing.

I have a feeling that the old chip was okay and there's something wrong with the board. Of course, the new chip you got could be bad, but it's unlikely for it to be bad in exactly the same way. Lift the new chip off and measure on the board without the chip installed. Do you still get 50 ohms? If you do, trace the rail going to pin 8 and test all parts connected to it.

**budm** · 05-03-2013, 10:28 AM

Re: Polaroid FLM-3232 Dead 24V Rail

I should have asked him to take the resistance reading on the pads before installing the new IC.

**martyparish** · 05-03-2013, 10:33 AM

Re: Polaroid FLM-3232 Dead 24V Rail

Awesome guys thanks for the fast replies. I'll check the resistance with chip removed, although that was a tricky task for me to install (rookie)

**kerbsjacob** · 05-05-2013, 12:56 AM

Re: Polaroid FLM-3232 Dead 24V Rail

Just did one of these. Had intermittent PFC failure and low voltage on big 400v cap. Same symptom, no backlight. otherwise ok.Found there was two surface mount diodes in series connected to pin 8 of pfc chip. One was cracked and had intermittent connection. I found it by re soldering all pfc circuit components on PSU. When I went to re solder it, it came apart in the middle, an I know I didn't cause it to crack, pretty sure it was the cause. It was not a visable problem before I reflowed the solder. I don't know what kind if Zener it should be, only has yellow stripe,no info on diode or board. I installed 5.1v Zener and I works, but who knows for how long. The other one in series looks the same and is 5.1 v, but others on the board look the same and are higher voltage. Cap voltage now 300 at first , but droops to 233v, but continues working.

Main point , check surface mount diodes.

Does anybody know what the right value is it should have? Or possibly have a working supply that could be tested to find Zener voltage of the diode?

**martyparish** · 05-05-2013, 10:40 AM

Re: Polaroid FLM-3232 Dead 24V Rail

Hey kerbsjacob, that's awesome and thanks for the info. What's crazy is that yesterday I was taking a hard look at these two diodes thinking one or both could be my issue. Now you come along with this info!

Can you take a peek at this photo and tell me if the diodes that I circles are the ones you are referring to?

Thanks!

Attached Files

**martyparish** · 05-07-2013, 05:23 AM

Re: Polaroid FLM-3232 Dead 24V Rail

It looks like kerbsjacob hit the nail on the head. I also had a broken diode connected to pin 8.

I used the L6561 datasheet referenced in my first post(or budm's post) to get these part numbers. (see attachment)

1N4150 (DIODE SWITCHING 50V 0.3A DO35)
1N5248B (DIODE ZENER 18V 500MW DO35)

Hopefully these are correct and fix my problem. I will report back when I replace them.

Polaroid FLM-3232 Dead 24V Rail

Polaroid FLM-3232 Dead 24V Rail

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