Philips 32PFL5322D/37 power supply repair

[rpgruss]

Re: Philips 32PFL5322D/37 power supply repair

There are 4 diodes under the heat sink. I've been probing around, and the 9v appears until I cross the diodes, then the voltage drops to 0. If I measure the voltage drop across the diodes, it is 9v. Checking in diode test mode shows all diodes with 154 ohms resistance on the inner two, and 158 ohms on the outer two. Putting the probes in reverse the reading rises, so it looks like they are not forward conducting.

Normally when I test diodes the resistance is in the 500 ohm range. Could I be onto something, or look somewhere else?

By the way, the diodes are connected directly to the secondary side of the larger transformer on the anode side.

Edit: One more thing I noticed: I encountered 18.4v on the board while tracing. It is present on the connector for the inverter board. Now everything I've read indicates inverter boards use 24v power. And 1/2 of 18.4 is right about 9v (I saw 9.14v). Could this be a clue?

[Mr Bill]

Re: Philips 32PFL5322D/37 power supply repair

Here is a picture of the power board with the heatsinks removed. I'm in the same boat. I've got this same tv and i'm getting the 5v supply protection error.

[retiredcaps]

Re: Philips 32PFL5322D/37 power supply repair

Checking in diode test mode shows all diodes with 154 ohms resistance on the inner two, and 158 ohms on the outer two. Putting the probes in reverse the reading rises, so it looks like they are not forward conducting.

Normally when I test diodes the resistance is in the 500 ohm range. Could I be onto something, or look somewhere else?

In circuit testing could be lowering the value of the readings.

PS. The unit of measurement that a digitial multimeter uses for a diode test is voltage. So you have 158 millivolt not ohms.

[retiredcaps]

Re: Philips 32PFL5322D/37 power supply repair

Now everything I've read indicates inverter boards use 24v power. And 1/2 of 18.4 is right about 9v (I saw 9.14v). Could this be a clue?

If 12V is measuring 9 and 24V is measuring 18.4V, I wonder if the SMPS chip is working properly or something in the feedback mechanism is broken?

[PlainBill]

Re: Philips 32PFL5322D/37 power supply repair

If 12V is measuring 9 and 24V is measuring 18.4V, I wonder if the SMPS chip is working properly or something in the feedback mechanism is broken?

Excellent point. That sounds like a problem in the resistors associated with the TL431 shunt regulator.

PlainBill

[retiredcaps]

Re: Philips 32PFL5322D/37 power supply repair

U651 might be the TL431. If not, it might be on the backside around the same area?

[retiredcaps]

Re: Philips 32PFL5322D/37 power supply repair

If 12V is measuring 9 and 24V is measuring 18.4V, I wonder if the SMPS chip is working properly or something in the feedback mechanism is broken?

Math oriented viewers might notice that the above ratios imply the power supply is working only at 75% for both voltages.

[Mr Bill]

Re: Philips 32PFL5322D/37 power supply repair

U651 might be the TL431. If not, it might be on the backside around the same area?

I checked my power supply and U651 & U240 are TL431C

[PlainBill]

Re: Philips 32PFL5322D/37 power supply repair

I checked my power supply and U651 & U240 are TL431C

There are two possibilities - the SMPS is current limiting because of excessive primary current, or something is affecting the voltage divider setting the output voltage. The quick and simple test is to measure the voltage on each pin of the TL431s. One should be at 0 volts, one at 2.5 volts and the third will be somewhat higher. U240 is the regulator for the standby supply; U651 is for the main supply. Oh, and a picture of the bottom of the power supply would be useful.

PlainBill

[tom66]

Re: Philips 32PFL5322D/37 power supply repair

Those red caps look like they are bulging (primary side, top of board.)

On half-bridge converters, if these bulge, you will get low output voltages or a power supply that does not work under load.

[Mr Bill]

Re: Philips 32PFL5322D/37 power supply repair

Those red caps look like they are bulging (primary side, top of board.)

Tom,
Are referring to C538 & C539? The picture above isn't rpgruss board, it's mine. I've got the same tv but i'm getting the 5v protection fault whereas he is getting the 12 volt protection fault.

On half-bridge converters, if these bulge, you will get low output voltages or a power supply that does not work under load.

As for my situation i'm only getting 5 volt standby. If i try to turn the supply on with a 3.3k resistor i still get almost no voltages other than the 5 volt standby. When you turn my set on the blue light comes on for a couple seconds like it wants to turn on then the red light starts flashing the 5v protection fault. Does this sound like a symptom those "red" caps could cause?

Thanks

[tom66]

Re: Philips 32PFL5322D/37 power supply repair

Tom,
Are referring to C538 & C539? The picture above isn't rpgruss board, it's mine. I've got the same tv but i'm getting the 5v protection fault whereas he is getting the 12 volt protection fault.

It may be a potential cause of the problem. It is on Vestel sets.

[Mr Bill]

Re: Philips 32PFL5322D/37 power supply repair

It may be a potential cause of the problem. It is on Vestel sets.

The part number is
BC 15n J 630v
375 KP/MKP S 0722

Trying to find the correct datasheet, this is an AC and Pulse metallized polypropylene film capacitor? I've never replaced one.

I take it if i find what it is i can check the capacitance and the esr?

Thanks

[tom66]

Re: Philips 32PFL5322D/37 power supply repair

The part number is
BC 15n J 630v
375 KP/MKP S 0722

Trying to find the correct datasheet, this is an AC and Pulse metallized polypropylene film capacitor? I've never replaced one.

I take it if i find what it is i can check the capacitance and the esr?

Thanks

It's a 15nF 630V rated capacitor. You can't check it for ESR because it has a very low capacitance. I'm not sure if capacitance would be useful, but try and check it.

The most common failure mode is for a bulge mark to appear in places on the capacitor where it is not of uniform thickness. These capacitors are really insufficient for the application they are used in, which is why they commonly fail.

[Mr Bill]

Re: Philips 32PFL5322D/37 power supply repair

My meter only goes down to 1uf. I'll order a couple 0.015 uf caps from digikey on my next order just to see if it solves my issue. I'm only risking $1

Thanks

[rpgruss]

Re: Philips 32PFL5322D/37 power supply repair

Wow, this thread has exploded!

I checked U240 and U651, U240 appears to be operating normally. The voltages are:

Pin 1: 2.47v
Pin 2: 0v
Pin 3: 3.67v

However, something appears to be amiss in U651, which PlainBill states is the main supply:

Pin 1: 1.84v
Pin 2: 0v
Pin 3: 7.29v

Which means the main regulator is running at 75% of the voltage of the standby regulator.

I switched U651 with a TL431 I had on a scrap board. The results are the same, still have low voltage on the 12v rail. All the resistors in the area of U651 are surface mounts, I checked their resistance and 2 of them read a lower resistance than stated on the label. Not sure if that is due to being in circuit or not, if you guys think it's worthwhile I'll pull them later and check the value out of circuit.

[tom66]

Re: Philips 32PFL5322D/37 power supply repair

My meter only goes down to 1uf. I'll order a couple 0.015 uf caps from digikey on my next order just to see if it solves my issue. I'm only risking $1

Thanks

Just make sure they are 630V rated parts (and polypropylene), otherwise you'll enjoy some fireworks .

[retiredcaps]

Re: Philips 32PFL5322D/37 power supply repair

However, something appears to be amiss in U651, which PlainBill states is the main supply:

Pin 1: 1.84v
Pin 2: 0v
Pin 3: 7.29v

Which means the main regulator is running at 75% of the voltage of the standby regulator.

I switched U651 with a TL431 I had on a scrap board.

I believe Pin 1 is the key. It should be 2.5V DC as a reference voltage. Find out what feeds pin 1.

[PlainBill]

Re: Philips 32PFL5322D/37 power supply repair

Wow, this thread has exploded!

I checked U240 and U651, U240 appears to be operating normally. The voltages are:

Pin 1: 2.47v
Pin 2: 0v
Pin 3: 3.67v

However, something appears to be amiss in U651, which PlainBill states is the main supply:

Pin 1: 1.84v
Pin 2: 0v
Pin 3: 7.29v

Which means the main regulator is running at 75% of the voltage of the standby regulator.

I switched U651 with a TL431 I had on a scrap board. The results are the same, still have low voltage on the 12v rail. All the resistors in the area of U651 are surface mounts, I checked their resistance and 2 of them read a lower resistance than stated on the label. Not sure if that is due to being in circuit or not, if you guys think it's worthwhile I'll pull them later and check the value out of circuit.

OK, a brief explanation of the TL431. It acts like an adjustable zener diode. In this application no current flows from pin 3 to pin 2 until pin 1 reaches 2.5 volts. Pin 3 is tied to the cathode of the LED in the optocoupler, the anode of the LED is tied to some higher voltage source.

The readings mean the SMPS is current limiting due to excessive current in the primary (or there is a problem that causes the apparent current to be higher than normal). Note the partial schematic I've attached. Q804 is the power FET. The drain of Q804 is goes to ground through R805, a 0.27 ohm, 2 watt resistor. Every time Q804 is turned on the pulse is fed through R807, filtered by C811 and C812, and fed to the CD input of the SMPS controller.

PlainBill

[rpgruss]

Re: Philips 32PFL5322D/37 power supply repair

Looking on the primary side, I don't see anything immediately obvious. The only thing I can see is resistor R526. According to the color code, it should be 1.6k ohm, but on my meter reads 0.99k ohm. This may be nothing as there were other resistors that did not follow the standard color code.

Any other places to look?