Polaroid TLU-03723B with overheating problem

[SuperSkippy]

I've been trying to fix this Polaroid TLU-03723B TV for some time, and I've got stuck.

The big picture problem is that the TV comes on for a period of between 1 hour and 2 hours, then turns off.

Please see attached pictures of the power supply.

[SuperSkippy]

Re: Polaroid TLU-03723B with overheating problem

This sounds like an overheating problem to me. If you look at the middle photo, the entire top left metal heatsink(?) gets increasingly hot when the TV is on, until it is almost too hot to touch.

This power supply has voltages of 5, 12, 18v, 24v and 30v. All voltages are present and correct on the output. The 5v is standby voltage- it's always there when there is power to the set. All the other voltages only appear when the TV is turned on.

When the TV turns itself off, it will not turn on again until some time has passed. During that time there is voltage on the filter caps, but no voltages from the output (not even standby power) and the transformers are not switching.

The right hand photo is the power supply with the metal top covers/heatsinks removed. If you can see at 9 o'clock on the board, there is the heatsink that gets hot. Next to all the heatsinks are a thermistor. If you spray freeze spray on the thermistor and the heatsink when the set has turned itself off, it comes back on again when power is reapplied.

The heatsink that gets very hot has the secondary rectifier diodes attached to it. The secondary rectifier diodes have been removed, and all test as good with a forward voltage drop of 0.1Vish. All of the capacitors test as good with my ESR meter, but I haven't removed and tested them individually, and since a lot are in parallel, I haven't been able to confirm that they have the right capacitance.

[SuperSkippy]

Re: Polaroid TLU-03723B with overheating problem

I tried running the TV with the heatsink detached altogether. I sprayed freeze spray on all of the diodes, then turned the TV on with the heatsink removed. The diodes on the 24V supply melted first and quickly. Since that's also where the thermistor was, I surmised that the 24V line was worthy of further investigation.

I think the 24V line is used to power the inverter board. The inverter board is made by Darfon (yay!), but all of the transformers ring good. I managed to insert my multimeter into current mode in the 24V line, and found that the TV was drawing just over 5A when turned on. The power supply board says that it can supply up to 7A, so that should be no problem. I didn't run the TV for long with the multimeter since it says on my multimeter 10 seconds max for current, so I don't know if that changes when the TV is running for a while.

[SuperSkippy]

Re: Polaroid TLU-03723B with overheating problem

Also note that there is a bodge resistor soldered to the bottom of the power supply board in the first picture. I don't know if it's a bodge done in the factory or whether someone has been here before me. It's attached between the 24V and the 12V output and is about 500Ω. I thought that it might be increasing load on the 24V line. I've removed it, all the voltages are the same and the TV still overheats.

[tom66]

Re: Polaroid TLU-03723B with overheating problem

My guesses would be, in order:
- Cold solder joint
- Bad startup capacitor
- Leaky MLCC (ceramic capacitor)
- Bad poly capacitor
- .... (large gap) ....
- Thermal cut off
- Divine intervention

[SuperSkippy]

Re: Polaroid TLU-03723B with overheating problem

I am depressed :-S. What would you do?

I can buy another PSU easily enough, do you think that will fix the problem, or do you think the problem is elsewhere in the TV?

[tom66]

Re: Polaroid TLU-03723B with overheating problem

No need to be depressed.

ALL of the voltages go away, including 5V standby? The standby supply is usually separate from the main supplies, BUT, it also often supplies the power to keep those running.

Therefore, I would focus my attention to that area first.

[SuperSkippy]

Re: Polaroid TLU-03723B with overheating problem

My guesses would be, in order:
- Cold solder joint
- Bad startup capacitor
- Leaky MLCC (ceramic capacitor)
- Bad poly capacitor
- .... (large gap) ....
- Thermal cut off
- Divine intervention

Wouldn't a cold solder joint and bad startup capacitor stop it from turning on at all?

[SuperSkippy]

Re: Polaroid TLU-03723B with overheating problem

No need to be depressed.

ALL of the voltages go away, including 5V standby? The standby supply is usually separate from the main supplies, BUT, it also often supplies the power to keep those running.

Yep, all of the voltages go.

If you look at my photo of the bottom of the board, there are two controller ICs, and there are separate transformers for the standby, and all the other voltages. (you probably already know this :-) )

[tom66]

Re: Polaroid TLU-03723B with overheating problem

Wouldn't a cold solder joint and bad startup capacitor stop it from turning on at all?

Both can be thermally dependent.

[SuperSkippy]

Re: Polaroid TLU-03723B with overheating problem

How hot do TV power supplies get in general? I don't have as much experience with them as you do.

[tom66]

Re: Polaroid TLU-03723B with overheating problem

Very hot. Which is part of the reason they don't last as long as they should. Generally they get hotter with the case off than on -- sounds odd? The case helps guide the air through the set and heatsinks. Maybe around 65°C is typical for a heatsink, but I've had burns from one heatsink before.

[SuperSkippy]

Re: Polaroid TLU-03723B with overheating problem

Results- I've just bought another power supply board, and that appears to be the TV fixed. It cost me £30 + VAT, which I felt was a reasonable cost if you value my time at anything more than 0.

[signup]

Re: Polaroid TLU-03723B with overheating problem

Hi Just had the same tv with identical problem

PSU= PWB-1038 Rev E2

IC Location W200/Primary Side really bad solder joints on all legs resoldered and all ok, also check the diode that is sitting right next to W200, it has had some heat put through it.

I also removed all the grey rock hard gunk around the fets and on the underside of the board that holds the bodged resistor in

Hope this helps someone with the same problem

[Knight2]

Re: Polaroid TLU-03723B with overheating problem

Hi Just had the same tv with identical problem

PSU= PWB-1038 Rev E2

IC Location W200/Primary Side really bad solder joints on all legs resoldered and all ok, also check the diode that is sitting right next to W200, it has had some heat put through it.

I also removed all the grey rock hard gunk around the fets and on the underside of the board that holds the bodged resistor in

Hope this helps someone with the same problem

Hi
I'm having the same issue with this model board.
NO bad caps, diodes,fuses all OK.
Removed all the hard gray glue type crap.
No dry joints,

It turn on with everything fine for around 10 mins , then everything goes off with a click.
Turns on again to do the same about three or four mins later. Please HELP

[CaBLeMaX]

Re: Polaroid TLU-03723B with overheating problem

i have same problem after 10 mins tv lose all power after unplug for short while it will work again all caps are fine i have replaced diodes but problem still remain

[ReeceyBurger123]

Re: Polaroid TLU-03723B with overheating problem

I have one in atm psu is a acbell pwb-1038 no 5vstby found that the main controller was blown along with the resistor but still no 5sbty also found a blown 18v zenner will get back to you if it gets the 5vstby back up. Anyone know any common issues with these power boards.

[johnboy1313]

Re: Polaroid TLU-03723B with overheating problem

Anyone know any common issues with these power boards.

Yeah, they tend to get hot and shut down.

[ReeceyBurger123]

Re: Polaroid TLU-03723B with overheating problem

Yeah, they tend to get hot and shut down.

Yeah I've seen I need some more resistors and that diode that I hope will get my 5vstby back alive.