Polaroid FLM-3232 No Sound, No Picture

[johnboy1313]

This set just came in this afternoon. I say no sound, no picture but I'm not certain because the backlights don't ever come on. I've tried the flashlight trick to look for a picture with my phone connected for audio but I can't tell if the menu is coming up and I have no idea what input this set was on when it went bad.

I do have 24V in standby (it's odd, but apparently normal for this set) when the power button is hit the red LED turns blue and I have 5.1V from the PSU along with 24V at the inverter. This follows the troubleshooting guide in the service manual and the blog below, so I'm assuming the PSU is working correctly.

http://blog.coppelltvrepair.com/2010...0804-0901.html

It looks like the 5.1V from the PSU travels through the main and is supposed to eventually wind up at the inverter to BL_ON, but I'm not seeing it.

At this point, I'm suspecting a bad main.

Here's a link to the SM
https://cdn.badcaps-static.com/pdfs/...a0215e68a9.pdf

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

So, as I dig into this thing a bit, I see that regulator U6 (1117L-18) in the red circle below is showing
0V
0V
1.3V

Where the regulator of the same kind, U4, in the yellow circle is showing
0V
1.8V
3.4V

It looks like the input to this VR is too low. Time to eat and do some more digging.

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

Part #'s on U6/U4?
Have you checked the DC-DC converters?

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

Both regulators are AS1117L-18. I'm not sure what a DC-DC converter is.

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

What's the part # on the 5 pin U1? That is a DC-DC converter IC.

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

1501A12 is the part number. So, as I'm working on this thing, there is a whine that has gotten more and more noticeable as I've worked. I still have 5.1v and 24v but the voltage across the big cap has degraded. It was 325v this afternoon as the whine has gotten louder, it has now dropped to 298v when powered on. When powered off it is 169v. I probably should have mentioned that but the fact that the voltages were correct I didn't worry about it.

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

Perhaps put a scope on the 24V line to find if it's stable?


Check pins:
- #1: Vin (3-42V)
- #4: 1.23V
- #5: <0.6V (if output is on)

Pin 2 should lead to an inductor (PCB designation Lxxx) and to a diode (Dxxx). The opposite end of Lxxx should go into the positive lead of a capacitor Cxxx. This is the output voltage. This only applies for a buck converter (output lower than input like an LDO) but the vast majority on main boards are only buck converters.

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

U1/1501A12 = 12V output
Pin #1 = 24.1V
Pin #4 = 12.3V
Pin #5 = 0.1V

U2/1501A50 = 5.0V output
Pin #1 = 24.1V
Pin #4 = 5.2V
Pin #5 = 0.1V

I'm off work this week so I won't be able to get the scope until next week.

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

Looks like they've used the fixed 5V/12V versions (hence "50" and "12" in part #s) instead. Those readings look good. I'd be considering eeprom or processor problem.

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

This isn't my TV. I posted an ad that I buy TVs and this guy called asking if I'd take a look at his. I'm not going to spend a ton of time on it and I don't think he wants to spend a ton of money.

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

I never do repairs for other people unless they're really close friends.

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

So, the owner of this thing didn't want to spend the money to fix it. He told me I could have it if I wanted it. To try to avoid having to put a PSU and a main board into it, I'd like to try to work on bringing the voltage across the big cap up to spec. Being that I'm very ignorant to the workings of a PFC circuit, in your opinion, is the low voltage measured across the big cap at power on likely due to it being bad?

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

The big cap itself can fail causing this problem, among other issues.

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

That was quick. Thanks. I'll swap out that cap and report back.

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

It is a Rubycon though. It takes a really bad power supply to kill a Rubycon.

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

Bad design or failure of another component? This TV isn't going to be worth a whole lot in working condition, so I'd really like to put as little as possible into it.

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

Bad design. The heatsinks alone form islands of contained heat, roasting the caps inside.

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

I had a chance to get into this set again last night. I found that even when I run a jumper from the 5.1V rail on the PSU through a 1K resistor to BL_ON, I still only measure .14V at BL_ON with no backlights. When I pull the wire from the plug on the inverter and run the jumper, the backlights come on at power on, the whining from the PSU stops, and I measure 5V at the BL_ON pin on the inverter. When I check the resistance between the end of the wire I pulled from the inverter plug and ground, it shows a short. There's definitely a fault in the 5.1V line of the mainboard.

Here's my issue. Even with the backlights on and the PSU not making the whining noise, I still see less than ~290V across the big cap. If I buy it by tomorrow, I can buy the main board for $31 shipped or the entire "control box", as they call it, containing the main board, the PSU, and the tuner board for $58 shipped. I really don't want to spend the extra money, but I'm not sure I can fix this PSU. I can't find a schematic anywhere.

[tom66]

Re: Polaroid FLM-3232 No Sound, No Picture

Do you have 5.1V when the main board is plugged in?

[johnboy1313]

Re: Polaroid FLM-3232 No Sound, No Picture

Yes and no. There is 5.1V at the blue wire from the PSU to the main at power on. There is a large connector on the back of the main board that connects the control box to the rest of the TV. I think I saw a post that you are familiar with this, I'm just documenting for anyone else that may be experiencing the same issue. Anyway, I see 5.1V at some of those pins, but not at the one that eventually connects to the inverter. Without a schematic, I'm not sure if the pins that I see 5.1V at are correct or not.