Philips lcd 32 inch no power

[weasel440]

hello all, i have been given a dead philips model 32PFL3504D/F7.
please bear with me. my lack of knowledge about tv's is not the greatest - still learning.

Symptom is no power. power light comes on for a couple of seconds then turns off, nothing else happens, but the ? thing circled in green buzzes slightly (thing with yellow tag).

I checked for power, but it l seem to lose power out of the plug circled in orange (red & black wire). i've also checked ohm / resistance on the cap circled in red and got no reading (large cap next to plug in question)?

any help would be greatly appreciated.

[Wrog]

Re: Philips lcd 32 inch no power

Attach pics as follows (using the forum guidelines please! no offsite hosting, use "Manage Attachments"): one with them all in place and connected, and one of each board (top/bottom). This will give a better overall look of how things work with this TV. The thing circled in green is a transformer -- one way to check to see if it is bad is to measure the resistance across the secondary. If you include a picture of the bottom, I'm sure someone can point out the test points. Instead of testing resistance across the cap, test voltage (negative lead typically goes to ground). Be careful! If you don't have all boards connected (or if something's not working quite right), the power supply board can hold a charge for quite some time and give a good shock!

[weasel440]

Re: Philips lcd 32 inch no power

ok maybe a mod can help me clean up / delete my origanal picture. can't seem to edit it? ty for the help.

[Wrog]

Re: Philips lcd 32 inch no power

A couple of assumptions: AC power comes into the 1st picture, top left corner? The connector that leads to the sub-board that includes the IR receiver and LED is one of the two red/black pairs at the bottom left board in 2nd picture? Pictures are too far away for me to identify the secondaries -- perhaps a more skilled person will step in and assist. In the meantime, inspect all of the solder joints to that transformer and reflow if there is any doubt.

In a nutshell, the way this TV should work is this: When power is applied, there should be 5V "standby" power that waits for the power button (either on the TV, or the remote) to tell it to turn on. At that point, the power supply clicks the relay to provide all of the various voltages to the mainboard and other sub-boards. The first step is to verify 5V standby is on and waiting. It sounds like it's on initially but goes out. There may be markings on the board indicating voltages expected at each of the connectors. I forgot to mention that if possible, try to get as close to 2000x2000 pixels with your pictures so we can see more detail.

[Dgtech]

Re: Philips lcd 32 inch no power

The service manual for this set can be found here:



When this thing is powered up, do you hear any relay click when the button is pressed?

[Dgtech]

Re: Philips lcd 32 inch no power

On page 41 of the service manual, there is a very nice schematic with voltage test points.
I hope this helps you at least narrow this thing down.

[weasel440]

Re: Philips lcd 32 inch no power

Ok just a little follow up.

If someone could chime in if i'm doing this correct, and what would cause the voltage drop?

In the photo I showed how I began testing with volt meter. The black spot @ (ac cord in) is what i hooked ground to. The red indicates the path i followed and some readings. all seems good till I got to the (D602) diode 1N5406 the voltage droped to 66.7 volts?

[PlainBill]

Re: Philips lcd 32 inch no power

Ok just a little follow up.

If someone could chime in if i'm doing this correct, and what would cause the voltage drop?

In the photo I showed how I began testing with volt meter. The black spot @ (ac cord in) is what i hooked ground to. The red indicates the path i followed and some readings. all seems good till I got to the (D602) diode 1N5406 the voltage droped to 66.7 volts?

That is probably normal. It looks like there are 4 resistors forming a bridge rectifier. Measure the voltage across the large capacitor with the power on.

You are making it difficult to assist you. This picture does cover the area of interest, but it should be taken from directly above the board. Take another one of the top side of the board, covering the same area, again from directly over the board, and with the same edge to the bottom of the picture. With those to it will be much easier to trace the circuitry.

There is a component that is not visible, it may be hidden behind the heat sink in the first picture.

PlainBill

[weasel440]

Re: Philips lcd 32 inch no power

[QUOTE=PlainBill;136226]Measure the voltage across the large capacitor with the power on.

I know this is probably a dumb question, but when checking do you have + & - on the capacitor, if so then I get no voltage. If I hook ground to where the main plug comes in and test each side of capacitor I get a reading of 66.7v. I probably should have been more specific in my last post - I'm only getting a volt reading of 66.7 for the rest of the power board.

[mbates14]

Re: Philips lcd 32 inch no power

You need to look at the inverter board.

I worked on one of these long long ago and the problem was in the inverter board.

[PlainBill]

Re: Philips lcd 32 inch no power

[QUOTE=weasel440;136240]

Measure the voltage across the large capacitor with the power on.

I know this is probably a dumb question, but when checking do you have + & - on the capacitor, if so then I get no voltage. If I hook ground to where the main plug comes in and test each side of capacitor I get a reading of 66.7v. I probably should have been more specific in my last post - I'm only getting a volt reading of 66.7 for the rest of the power board.

You should get a reading of about 165 volts across the large capacitor. There is a polarity. The lead of the cap with a strip on it is the negative side.

And I made a whopper of a mistake in my previous post. It should read "It looks like there are 4 diodes forming a bridge rectifier."

PlainBill

[weasel440]

Re: Philips lcd 32 inch no power

[QUOTE=PlainBill;136276][QUOTE=weasel440;136240] You should get a reading of about 165 volts across the large capacitor. There is a polarity. The lead of the cap with a strip on it is the negative side.

First I would like to thank everyones help so far. I'm new to electronic repair and trying to learn.

Ok I double checked for power at the large capacitor, when you first touch the leads to it - it will read 82v and drops to 0v in a split second, remove & retouch leads it read 120v then drops right to 0v. So would this mean the capacitor is bad or is it something that feeds the capacitor? Also is it normal for the transformer to slightly hum?

[retiredcaps]

Re: Philips lcd 32 inch no power

First I would like to thank everyones help so far. I'm new to electronic repair and trying to learn.

Ok I double checked for power at the large capacitor, when you first touch the leads to it - it will read 82v and drops to 0v in a split second, remove & retouch leads it read 120v then drops right to 0v. So would this mean the capacitor is bad or is it something that feeds the capacitor?

First if you are new to electronics, please be aware that the voltage at the main capacitor is enough to seriously do some harm to you. Be careful not to let the probes slip around. A couple of weeks ago, a newbie was probing around with his multimeter causing sparks and shorts. When it was suggested he take some to learn how to use his multimeter properly (he had the leads plugged into the wrong jacks on the multimeter), he threw a drama queen hissy fit. We were trying to WARN him of potentially lethal consequences of his actions.

Check to make sure your black lead is plugged into the COM jack. Red lead plugged into voltage jack. Your multimeter should be set on DC V. If it is manual, put it to the 200V DC range.

As PlainBill said, a good reading should be around 165V (120 V main voltage x 1.4 equals roughly 165V DC).

If your technique is correct in measuring the main capacitor and you still get fluctuating voltage still, there are other things to check. For example, with power off and tv unplugged from ac wall outlet, you can measure the bridge rectifier or 4 diodes for shorts. One of those diodes could be bad?

[weasel440]

Re: Philips lcd 32 inch no power

Ok I got power now, must have been a loose solder joint. I resoldered just about every conection.

Now onto the next problem / questions. The transformer is still buzzing. I've found a service manual and read through the trouble shooting section. It said to test some diodes, transistors, and i think it's called a voltage regulator (LD1117V). What is the correct way to test a voltage regulator? All diodes checked out ok, but I think I have 2 bad transistors. Please correct me if i'm wrong > when checking a transistor you should have a very close reading for the emitter & collector?

[weasel440]

Re: Philips lcd 32 inch no power

I was wondering where everyone orders there parts from? I'm looking for (LD1117V) low drop voltage regulator, (KTC3198) transistor & (2SC2120) transistor. perferably from one store to save on shipping.

[Agent24]

Re: Philips lcd 32 inch no power

My choices are either Farnell or RS-Components, or, eBay.

If you're in the USA you get Digikey and Mouser as well, and probably more.

[Wrog]

Re: Philips lcd 32 inch no power

What is the correct way to test a voltage regulator? All diodes checked out ok, but I think I have 2 bad transistors. Please correct me if i'm wrong > when checking a transistor you should have a very close reading for the emitter & collector?

To test the voltage regulator, red probe on center pin, black probe on ground with the power on. The 1117 usually has several additional numbers on the end to signify voltage -- for instance 1117-18 is a 1.8V, -33 is a 3.3V, etc. As for the transistors, test resistance between 1-2, 2-3, 1-3 and then reverse black/red and do the same measurements. Anything close to 0 ohms indicates a short and it needs to be replaced.

[weasel440]

Re: Philips lcd 32 inch no power

The LD1117V is a "adjustable" low drop voltage regulator. According to the service manual schematics it says when checking should be +3.3v, so my question is would it be safe to use a 3.3v low drop voltage regulator or should i stick with the adjustable one. Seems easier to find the "fixed" low drop regulators then the "adjustable" ones.

[weasel440]

Re: Philips lcd 32 inch no power (Updated)

hello again,

I ordered a used board from ebay and installed it. The buzzing sound went away, but it still won't power up? If I unplug the cable "circled" the power light will stay lit, but no screen?

Could it be the inverter board like (mbates14) suggestted? Or could it be that I got a junk board from ebay?

[weasel440]

Re: Philips lcd 32 inch no power