Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

[curt2199]

This is my second TV repair attempt after repairing a Phillips with a similar issue.

I picked this TV up for $20 to attempt to repair it and put it in the kids room. The previous owner said recently it would stay on for up to a couple hours until more recently it would only turn on with no picture. I tried pushing the menu button with the TV on and shining a flashlight on it and am not seeing any signs of a picture which would normally indicate the backlight inverter out like the last TV I repaired.

I found a thread with another Polaroid tv with the same power supply as mine and have been trying to find the failed capacitors or diodes without any luck. https://www.badcaps.net/forum/showthread.php?t=27692

I pulled the diode at Z9 and it shows a rating of around 650 in one direction and 1 in the other with the diode check on my multimeter which I believe means it's ok from what I've read. I also checked the 3 x 1000uf caps near the corner of the board that are normally notorious for going bad as they are cheap. I pulled and inspected them and they are Rubycon (which I understand are very good). I have 3 new ones I picked up from Radio Shack but am hesitant to install them since these look and should be fine.

I'm not really sure where to go next.

[Th3_uN1Qu3]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Leave the original caps in there. Take some pictures of the guts of the TV and post them, and make some voltage measurements on the power supply and inverter.

[budm]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Probably should move this thread to the TV section.

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Sorry for the wrong forum, I used the link from the post I linked to before realizing that one was in the wrong forum as well.

Anyway I did some voltage checks tonight with power/blue light on. I am hearing a very faint random buzz coming from the power supply. My Z9 diode connection is solid although the solder doesn't look the best.

I have circled and wrote values on the pictures. Values with 23.8V and 0.4V where indicated on the large photo.

[budm]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

What DC voltage do you get at the TWO LEGS of the main filter, the one laying side way with the wrapping coming off half way, when TV is powered off and then powered on?
That big cap does not look normal.

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

I'm not sure what you mean by the filter. I know most of the basic electrical pieces. The only thing I have with wrapping coming off is the big capacitor and the voltage at that cap with the power off is 63.5V and with power on its 62.6V. This also is the general area of the random buzzing noise.

Also I'm using the metal TV chassis for ground. Should I be grounding to something else?

[budm]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

"The only thing I have with wrapping coming off is the big capacitor" that is the main filter cap, you have to measure the DC voltage RIGHT AT THE TWO LEGS, you cannot use the chassis ground as the ground ref point when you are working in the Primary (hot) side of the circuit, the negative leg of that filter cap is the ground ref point for the primary circuit side.

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Was just coming back to correct that as I realized I measured that wrong. I'm showing 170V across that big capacitor both on and off. I also found the following site that's helped and am stepping through those checks. http://blog.coppelltvrepair.com/2010...0804-0901.html.

I can tell you with Power on and blue light I am getting 5V on the PS_On pin but I am not getting voltage at the CN2 connector's 24V pins with power on. I also am not getting voltage at CN4 and CN5 (small 2 pin connectors with nothing connected to them) which from reading I believe should be around 24V.

[budm]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

OK, that means the PFC voltage is not working, the 24V power supply will not function until the PFC Voltage booster is working first since it requires 360~400VDC for the 24V power supply section to work. The voltage on that cap should go up from 170V to 360~400VDC range. The PFC IC controller may be bad, the MOSFET for the PFC, the PFC Diode, etc.
Too bad the info at that site does not mention anything abut PFC Voltage booster circuit.
That filter cap, did you check the value? It does not look good when the shrink tubing shrinked down like that.

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

I haven't checked the filter cap as I don't have an esr tester. If that cap is bad (obviously shows signs of excessive heat and probably a cheap cap), would it be the reason for the low voltage? And is it possible to test that cap without and esr tester?

[Th3_uN1Qu3]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Replace it, it's a few bucks... And yes, if that capacitor went bad, it is possible that it caused something in the PFC circuit to blow, hence the low voltage. Unfortunately, simply replacing that cap isn't likely to bring the voltage back up, but it's the first step you should take.

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Moving ahead here I followed the steps in this thread to test the PFC IC. Budm, you have been a busy guy, jeesh. Really appreciate the help. I'll be ordering a replacement big cap for this as well if I can find the break point.

In testing the IC, I found that I am showing similar resistance values with power off and disconnected except my PIN 8 did not show a 50 ohm resistance, it was OL like the others. Upon plugging power the voltage from pin 6 to pin 8 read 0.95V (red light) and when powered on (blue light) the voltage showed 10.8V.

Does this indicate a bad IC? Looks like the Min voltage range for the IC at pin 8 is 11?

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Well, the TV is on. I am not entirely sure what I did to fix it unless it is perhaps the diodes that are mentioned in that last thread near the end (18V and 50V). I tried testing for resistance across them but didn't get a reading (maybe not doing it right). Decided to to power the set test voltage across them and the test powered on normally. I am showing 11V across one and 5.7V across the other.

Wondering if for sure it is one of these diodes that is possibly cracked like the other post mentioned... I'll call this a success so far as the TV is on now. lol

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

TV is back to not working/flickering sometimes. I found that I had better luck with the power supply upside down and laying on a pad of paper (to avoid contact with chassis) as this is how I had it working when testing the voltage on the IC. I looked over the diodes more and am just not seeing any cracks in them but unless I'm crazy, the want reading 5.6-5.7 may be the culprit as I pushed prodded one side of it while the backlight was off and it started flickering on. I now cannot get the backlight to kick on or at least stay on constantly and I'm back to showing 10.7-10.8V at PIN 8 and across one of the diodes (which read 11V when the backlight was lit)

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Ok, I had a chance to do some more testing and I found it! I've attached a photo of the cracked diode. Pushing on one side of it causes the buzzing noise to stop and backlight to remain constant so I know 100% this is the culprit.


Now how do I go about identifying this diode and is it possible to solder a standard small diode from Radio Shack in it's place or do I need to find an exact match?

Thanks!

[whiz62]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

What did you finally do about the diode?

[curt2199]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

What did you finally do about the diode?

Replaced it with one of these and it's working great!

http://www.ebay.com/itm/BZV55-C5V6-P...item1c33f1ca9b

[whiz62]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

Thanks. Just got this thing and removed Z9 diode and it appears to be ok. The diode you refered to is not cracked so I suppose I should get back to basics and check voltages. All caps have are not buldged and have low esr.

[whiz62]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

I checked the diodes on back and the one next to the one you replaced was open. I removed it and it had cracked in two pieces. I was in a hurry and no one sells sm diodes in town so I went to radio shack and got an axial zener close to the value of the original.

Now I have backlights but no picture or sound. Removed t-con and checked the fuse F1 and it is not blown. This thing has had a rough life. Looks like a ten year old tried to take it apart to repair. the cable to t-con is missing the metal clip that holds it to board so i had to tape it down to hold it in place.

Just wondering if anyone has had this model with no picture or sound but does have backlights.

Thanks for the tip on the diodes.

[budm]

Re: Polaroid FLM-323B Powers on, No Picture, Only powers off with cord.

What DC Voltage do you get at both ends of the fuse with ref to chassis ground when TV is ON?