Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

[Dannyx]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Take a picture of the bottom of the board too. What do you get on the main filter cap ? Be very careful when measuring this - DANGEROUS !

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Take a picture of the bottom of the board too. What do you get on the main filter cap ? Be very careful when measuring this - DANGEROUS !

that's the big huge cap correct? should I put the meter in AC or DC when measuring? and what should I know in terms of safety? do I measure it with power going to the board or not? what's the proper way to test it? do I put the negative probe on the negative side of the cap and positive to the positive side or do I put the black to the chassis ground of the TV and touch the red probe to the positive side of the cap? I attached a picture of the bottom of the PS board as well as a top shot again.

[Dannyx]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

that's the big huge cap correct?

Correct

should I put the meter in AC or DC when measuring?

DC of course

what should I know in terms of safety?

Well OK, I may have exaggerated a bit, it's just common sense at the end of the day. Very high voltages can be present on that cap. It's got a booster circuit as well from what I can tell, so it can reach 380v easily - not something you want to touch. You touch 12v or 24v on the secondary...ok, not so bad - may feel an uncomfortable tingle, but 380v will definitely hurt. I experienced it myself and it was NOT fun, especially since I somehow grabbed the board in such way that it went through my chest (one hand was touching +, the other hand was on ground or chassis somewhere).

do I measure it with power going to the board or not? what's the proper way to test it? do I put the negative probe on the negative side of the cap and positive to the positive side or do I put the black to the chassis ground of the TV and touch the red probe to the positive side of the cap?

You'll have to measure it live, while plugged in that is, hence the warning I gave above. *Crash course on power supplies*: a SMPS (switch-mode power supply) is divided into two halves: a HOT (or primary) side and a COLD (or isolated/secondary side). These will be clearly marked out and labeled on all but the cheapest, dirtiest boards (Notice how there's a dotted line separating the two halves). As the name "isolated" suggests, the secondary side is isolated from the mains, thus each side has its own ground point, so there will be a HOT ground and a COLD ground. The chassis will never be connected to HOT ground due to obvious safety reasons - it will be connected to COLD ground. Your main reservoir capacitor is on the HOT side, therefore you'll want to measure it with respect to HOT ground, which is the - of the bridge rectifier, the - of the cap itself and the - of any other components located on the HOT side. Give it a shot: place your red probe on the cap's + leg and the negative probe on its negative leg or on the - leg of the bridge rectifier (all on the HOT side). You'll have to do this on the bottom of the board so make sure your hands or probes don't slip - you may end up with a blown fuse and a jump-scare

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Correct

DC of course

Well OK, I may have exaggerated a bit, it's just common sense at the end of the day. Very high voltages can be present on that cap. It's got a booster circuit as well from what I can tell, so it can reach 380v easily - not something you want to touch. You touch 12v or 24v on the secondary...ok, not so bad - may feel an uncomfortable tingle, but 380v will definitely hurt. I experienced it myself and it was NOT fun, especially since I somehow grabbed the board in such way that it went through my chest (one hand was touching +, the other hand was on ground or chassis somewhere).


You'll have to measure it live, while plugged in that is, hence the warning I gave above. *Crash course on power supplies*: a SMPS (switch-mode power supply) is divided into two halves: a HOT (or primary) side and a COLD (or isolated/secondary side). These will be clearly marked out and labeled on all but the cheapest, dirtiest boards (Notice how there's a dotted line separating the two halves). As the name "isolated" suggests, the secondary side is isolated from the mains, thus each side has its own ground point, so there will be a HOT ground and a COLD ground. The chassis will never be connected to HOT ground due to obvious safety reasons - it will be connected to COLD ground. Your main reservoir capacitor is on the HOT side, therefore you'll want to measure it with respect to HOT ground, which is the - of the bridge rectifier, the - of the cap itself and the - of any other components located on the HOT side. Give it a shot: place your red probe on the cap's + leg and the negative probe on its negative leg or on the - leg of the bridge rectifier (all on the HOT side). You'll have to do this on the bottom of the board so make sure your hands or probes don't slip - you may end up with a blown fuse and a jump-scare

Ok I measured it and it all went well, no blown fuses or any of that sort. I got 347.0 Volts. Is that good or bad? what should I check next?

[Dannyx]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Ok I measured it and it all went well, no blown fuses or any of that sort. I got 347.0 Volts. Is that good or bad? what should I check next?

Was the measurement taken with the board ON (5v jumped to PS_ON pin) or OFF/standby ? If it was done WITH 5v on the PS_ON pin, 300 V on the main cap is not enough - it means the PFC booster is not working, since you should've read around 400v on that cap when the PSU is ON. From what I can see in the pictures, the boost circuit is comprised of two coils (the ones next to each other), the two large diodes next to those, one of those two transistors in the middle and the control IC in the middle of the bottom of the board. Given that your fuse is OK, the diodes and transistor are most likely fine - a shorted semiconductor immediately pops the fuse. When PFC is not working and nothing "big" is shorted, it's often something to do with the VCC for one of the ICs. If we're lucky it's just a dead cap somewhere, if we're unlucky we'll have to pull out the whole chip, but no need to dive into that just yet. Let me know how you're standing right now.

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Was the measurement taken with the board ON (5v jumped to PS_ON pin) or OFF/standby ? If it was done WITH 5v on the PS_ON pin, 300 V on the main cap is not enough - it means the PFC booster is not working, since you should've read around 400v on that cap when the PSU is ON. From what I can see in the pictures, the boost circuit is comprised of two coils (the ones next to each other), the two large diodes next to those, one of those two transistors in the middle and the control IC in the middle of the bottom of the board. Given that your fuse is OK, the diodes and transistor are most likely fine - a shorted semiconductor immediately pops the fuse. When PFC is not working and nothing "big" is shorted, it's often something to do with the VCC for one of the ICs. If we're lucky it's just a dead cap somewhere, if we're unlucky we'll have to pull out the whole chip, but no need to dive into that just yet. Let me know how you're standing right now.

The measurements were taken with the PS ON with it jumped and just the mains connected to it. I'm not sure what parts you are speaking of would it be possible to upload a circled picture using M$ paint on the parts your speaking of? tonight i'm going to try replacing a few caps that the service manual recommends if you are not getting 12V and 24V. Just so you know I do have the Shopjimmy parts kit for this PS board, but I rather find the issue instead of soldering 35 to 40 parts that's not all needed. I have soldered some already, but hauled to see if I could pinpoint exactly whats at fault here.

[Dannyx]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

This confirms what I was saying earlier: with PS_ON connected to 5v, there should be around 400v on the main cap - PFC is not starting. If you're lucky, one of those caps you'll replace will solve the issue, though I'd personally start looking around the PFC IC and measure some voltages.

Let's continue the crash course on SMPSs. Booster circuits: there are 2 coils (or inductors if you prefer) labeled L1603 and L1604 on the left side of your board. They are switched on and off very rapidly by those two transistors next to them, labeled Q1601 and Q1602 from what I can make out. When the coil is de-energized (transistor is off/open) the collapsing magnetic field generates a voltage which is rectified by diodes D1604 and D1606 and "stuffed" into the main cap. As this is happening, we're stuffing the cap with even more voltage straight from the bridge rectifier, thus getting close to 400v. Those transistors are controlled by IC1401 from what I can make out (bottom of the board, far-right side - my mistake the first time around, as it's not the one in the middle upon closer inspection). Something's not functioning correctly here. As I said, it's usually caused by a problem on the VCC bus powering the IC. I don't know what IC it is and what its requirements are (feel free to look up a datasheet to be really thorough), but you can probably get away with simply measuring the jumpers leading there: notice the jumpers labeled HOT GND and HOT +15v on the top side of the board right around where the IC is, so you can easily stick your probes on those and see if you're indeed getting 15v. If you're not, there's a lonely cap right there which you should try replacing - it's for that VCC I was mentioning. If you ARE getting 15v or thereabouts, something else is acting up and troubleshooting will become increasingly more difficult, although you should still replace that cap just to rule it out. Let us know how it goes.

[budm]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Also check the RESISTANCE of D1604, 1606 to make sure they are not shorted or has low Ohm leakage resistance.

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Also check the RESISTANCE of D1604, 1606 to make sure they are not shorted or has low Ohm leakage resistance.

I just checked them now and they are both at 477 Ohms and read only one way reversing the leads gives me a 0L reading. Do they test good?

[Dannyx]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

I just checked them now and they are both at 477 Ohms and read only one way reversing the leads gives me a 0L reading. Do they test good?

Yes, if they were bad ("leaky"), they would've conducted both ways which is not desirable. Like I previously said: if the fuse is OK, it's unlikely any major semiconductor is damaged - rule of thumb.

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

This confirms what I was saying earlier: with PS_ON connected to 5v, there should be around 400v on the main cap - PFC is not starting. If you're lucky, one of those caps you'll replace will solve the issue, though I'd personally start looking around the PFC IC and measure some voltages.

Let's continue the crash course on SMPSs. Booster circuits: there are 2 coils (or inductors if you prefer) labeled L1603 and L1604 on the left side of your board. They are switched on and off very rapidly by those two transistors next to them, labeled Q1601 and Q1602 from what I can make out. When the coil is de-energized (transistor is off/open) the collapsing magnetic field generates a voltage which is rectified by diodes D1604 and D1606 and "stuffed" into the main cap. As this is happening, we're stuffing the cap with even more voltage straight from the bridge rectifier, thus getting close to 400v. Those transistors are controlled by IC1401 from what I can make out (bottom of the board, far-right side - my mistake the first time around, as it's not the one in the middle upon closer inspection). Something's not functioning correctly here. As I said, it's usually caused by a problem on the VCC bus powering the IC. I don't know what IC it is and what its requirements are (feel free to look up a datasheet to be really thorough), but you can probably get away with simply measuring the jumpers leading there: notice the jumpers labeled HOT GND and HOT +15v on the top side of the board right around where the IC is, so you can easily stick your probes on those and see if you're indeed getting 15v. If you're not, there's a lonely cap right there which you should try replacing - it's for that VCC I was mentioning. If you ARE getting 15v or thereabouts, something else is acting up and troubleshooting will become increasingly more difficult, although you should still replace that cap just to rule it out. Let us know how it goes.

Ok done for tonight it's 2AM lol, anyhow tonight I replaced C1725, C1727 and C1728. Also replaced C1736 and C1737 also did a reflow using flux and the drag soldering method on IC1401. Hooked it to just the mains jumped it and did measurements the same results, still ridiculously low on the 12 and 24 volt rails. Wednesday night I will continue and check what you suggested above. I also have a brand new IC1401 here that I could replace it came with the shopJimmy repair kit for this board. Do you think IC1401 could be at fault or something around it?

[Dannyx]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Ok done for tonight it's 2AM lol, anyhow tonight I replaced C1725, C1727 and C1728. Also replaced C1736 and C1737 also did a reflow using flux and the drag soldering method on IC1401. Hooked it to just the mains jumped it and did measurements the same results, still no 12 or 24 volts. Wednesday night I will continue and check what you suggested above. I also have a brand new IC1401 here that I could replace it came with the shopJimmy repair kit for this board. Do you think IC1401 could be at fault or something around it?

Could be...can't tell until you measure its VCC and possibly replace the IC afterwards if VCC seems ok.

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Could be...can't tell until you measure its VCC and possibly replace the IC afterwards if VCC seems ok.

Understandable, I will continue on Wednesday night and report back my findings. Thank you.

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

This confirms what I was saying earlier: with PS_ON connected to 5v, there should be around 400v on the main cap - PFC is not starting. If you're lucky, one of those caps you'll replace will solve the issue, though I'd personally start looking around the PFC IC and measure some voltages.

Let's continue the crash course on SMPSs. Booster circuits: there are 2 coils (or inductors if you prefer) labeled L1603 and L1604 on the left side of your board. They are switched on and off very rapidly by those two transistors next to them, labeled Q1601 and Q1602 from what I can make out. When the coil is de-energized (transistor is off/open) the collapsing magnetic field generates a voltage which is rectified by diodes D1604 and D1606 and "stuffed" into the main cap. As this is happening, we're stuffing the cap with even more voltage straight from the bridge rectifier, thus getting close to 400v. Those transistors are controlled by IC1401 from what I can make out (bottom of the board, far-right side - my mistake the first time around, as it's not the one in the middle upon closer inspection). Something's not functioning correctly here. As I said, it's usually caused by a problem on the VCC bus powering the IC. I don't know what IC it is and what its requirements are (feel free to look up a datasheet to be really thorough), but you can probably get away with simply measuring the jumpers leading there: notice the jumpers labeled HOT GND and HOT +15v on the top side of the board right around where the IC is, so you can easily stick your probes on those and see if you're indeed getting 15v. If you're not, there's a lonely cap right there which you should try replacing - it's for that VCC I was mentioning. If you ARE getting 15v or thereabouts, something else is acting up and troubleshooting will become increasingly more difficult, although you should still replace that cap just to rule it out. Let us know how it goes.

Ok so before I went to work I had time to probe the jumpers labeled HOT GND and HOT +15v on the top side of the board right around where the IC is and there is absolutely no voltage there its dead, so I went ahead and replaced the lonely cap right there that you recommended and jumped the power supply with just mains connected and still the same results, still very low 12 and 24 volt rails and the jumpers labeled HOT GND and HOT +15v on the top side of the board right around where the IC is still dead. How shal I proceed now? please advise. Thanks.

[Dannyx]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Ok so before I went to work I had time to probe the jumpers labeled HOT GND and HOT +15v on the top side of the board right around where the IC is and there is absolutely no voltage there its dead, so I went ahead and replaced the lonely cap right there that you recommended and jumped the power supply with just mains connected and still the same results, still very low 12 and 24 volt rails and the jumpers labeled HOT GND and HOT +15v on the top side of the board right around where the IC is still dead. How shal I proceed now? please advise. Thanks.

The schematic would come in handy at this point to see where those 15v are supposed to come from...from what I've been able to track in the pictures, is should be coming from D1250, a diode near the small transformer on the side of the board.

*more SMPS theory* the VCC for running the various ICs on the HOT side is usually derived from an auxiliary winding on one of the transformers (if the board has more than 1, which is the case here). It is rectified by a diode and fed to the various ICs. Check D1250 for shorts (highly unlikely) and measure if it puts out anything: red probe on the cathode (striped) side of the diode and black probe on the capacitor's negative leg or the rectifier's negative leg or ANY other negative leg on the HOT side. Those jumpers I told you about should come in vary handy for picking up a HOT ground as they help keep the probe steady and make good contact...

[CDRW]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Check the voltage vcc and v aux on the power supply chip. Transistors Q1401 and Q1402

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

The schematic would come in handy at this point to see where those 15v are supposed to come from...from what I've been able to track in the pictures, is should be coming from D1250, a diode near the small transformer on the side of the board.

*more SMPS theory* the VCC for running the various ICs on the HOT side is usually derived from an auxiliary winding on one of the transformers (if the board has more than 1, which is the case here). It is rectified by a diode and fed to the various ICs. Check D1250 for shorts (highly unlikely) and measure if it puts out anything: red probe on the cathode (striped) side of the diode and black probe on the capacitor's negative leg or the rectifier's negative leg or ANY other negative leg on the HOT side. Those jumpers I told you about should come in vary handy for picking up a HOT ground as they help keep the probe steady and make good contact...

Ok guys back at it for another round. I did the above and D1250 is not shorted. I also measured if it's outputting anything and it is. It's outputting 15.44 Volts. We also have to back up a second here. I must of been still half asleep this morning because when you advised me to probe the jumpers labeled HOT GND and HOT +15v on the top side of the board right around where the IC is I messed up and didn't measure correctly, I was measuring both grounds. After correctly measuring it there is 14.70 Volts there, not 0 as I previously thought, stupid me for probing both grounds. I'm glad I re-checked that, not sure if that changes anything or the direction of what I should check next.

Well things just turned for the worst. I was probing the IC1401 for voltages and I'm sure I didn't jump anything as I was super careful, but I blew the fuse. I replaced it with the same kind just to plug it in and immediately blow it again and this time there was a spark near Q1701, not sure if that means anything as I don't see any physical burns or anything of the sort. So now I caused a second problem. Now what?

For what it's worth here was the readings I got from IC1401 before stuff turned for the worst...

Pin 1 = 0.242

Pin 2 = 6.040

Pin 3 = 2.894

Pin 4 = 5.985

Pin 5 = 0

Pin 6 = 2.538

Pin 7 = 4.265

Pin 8 = 0.048

Pin 9 = 0.003

Pin 10 = Jumps from 0 to 0.600 and back to 0 does this constantly.

Pin 11 = Kaboom fuse blows as soon as I touched the pin.

[budm]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Did you download the service manual in the link of post #8?
Does the relay kick on when power supply is forced on?

[sfernandes]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Did you download the service manual in the link of post #8?
Does the relay kick on when power supply is forced on?

Yes I have the service manual. The relay does not click anymore since the fuse blew and when I replaced it, it blew again as soon as I forced it on. Before all these misshaps the relay would click when forced on.

[budm]

Re: Philips 55PFL3907/F7 Dead, No Standby LED, Nothing, Please Help

Yes I have the service manual. The relay does not click anymore since the fuse blew and when I replaced it, it blew again as soon as I forced it on. Before all these misshaps the relay would click when forced on.

Blown fuse is a very important missin data.
Then it no use to try to find out if you have VCC for the PFC or not, right now you need to find out why it blows the fuse when the relay comes on, as you can see the relay provides the AC to the bridge rectifier to provide DC to run the PFC circuit. So may be the bridge rectifier, PFC MOSFETs shorted out; that problem needs to be solved first.