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

[sfernandes]

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

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.

Yeah I understand that now that has to be solved first to continue with the original issue. My problem is that im kinda a newbie to some of this. How would I test the MOSFETS? and where are they located? Could they be tested in circuit?

[Dannyx]

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

Yeah I understand that now that has to be solved first to continue with the original issue. My problem is that im kinda a newbie to some of this. How would I test the MOSFETS? and where are they located? Could they be tested in circuit?

Yes, MOSFETs (metal oxide semiconductor field effect transistors BTW) can be tested in circuit quite easily: grab your meter, set it to continuity (beeping) and probe the 3 pins of the FET - doesn't really matter how you place the probes because FETs fail shorted and will indicate continuity anyhow if dead. You shouldn't get any continuity between any of the pins in continuity mode. IC1201 near the small transformer also contains a FET, even if doesn't look like it - it is the standby IC and needs to be checked also, though from what I understand the fuse pops only when the relay turns on, meaning the standby circuit is fine. There are 4 FETs on your board: two for PFC on the left side near the coils and two in the middle for the main transformer. Also check the bridge rectifier and PFC diodes (also on the left near the coils - we've discussed this) in the same fashion...highly unlikely they failed but worth double-checking. Would also be handy to tell us what the PFC IC you measured on the back is (part number).

ALSO: you're saying you saw a spark near Q1701. If the package of the transistor isn't blown apart, in which case THAT would be what sparked, check the snubber capacitor C1702 and see if it's got a hole in it. Snubbers sometimes fail like that and you have a hard time figuring out what the heck blew since they fail open and the meter doesn't pick it up and they're tucked away near other components making it hard to see if they're punctured or not....happened a lot to me on Sammy boards lately for some reason.

[sfernandes]

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

Yes, MOSFETs (metal oxide semiconductor field effect transistors BTW) can be tested in circuit quite easily: grab your meter, set it to continuity (beeping) and probe the 3 pins of the FET - doesn't really matter how you place the probes because FETs fail shorted and will indicate continuity anyhow if dead. You shouldn't get any continuity between any of the pins in continuity mode. IC1201 near the small transformer also contains a FET, even if doesn't look like it - it is the standby IC and needs to be checked also, though from what I understand the fuse pops only when the relay turns on, meaning the standby circuit is fine. There are 4 FETs on your board: two for PFC on the left side near the coils and two in the middle for the main transformer. Also check the bridge rectifier and PFC diodes (also on the left near the coils - we've discussed this) in the same fashion...highly unlikely they failed but worth double-checking. Would also be handy to tell us what the PFC IC you measured on the back is (part number).

ALSO: you're saying you saw a spark near Q1701. If the package of the transistor isn't blown apart, in which case THAT would be what sparked, check the snubber capacitor C1702 and see if it's got a hole in it. Snubbers sometimes fail like that and you have a hard time figuring out what the heck blew since they fail open and the meter doesn't pick it up and they're tucked away near other components making it hard to see if they're punctured or not....happened a lot to me on Sammy boards lately for some reason.

Ok back to the beginning I fixed the issue I caused it was blowing fuses because Q1601 was shorted I replaced it and replaced the fuse it's working again back to square one still low 24 volts and low 12 Volts. Where should I look now?

While I was waiting for a response i decided to go ahead and replace IC1401. I replaced it with a brand new one and same results still low 12 Volts and Low 24 Volts so IC1401 was not the issue. I should also note that I have tested every single diode on the board and none are shorted. Where should I look now?

[sfernandes]

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

How do I go about testing these? Do I do it with the board jumped on or do it with the board off? Where do I put my probes and where do I set the meeter to test these also what reading do I look out for? I have located and circled these two components on the board just don't know how I should test them. Please advise.

[Moreno83]

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

Can you post a picture of the part you are trying to measure? Usually a mosfet is labeled with "Q".
Meter in diode mode and the propes on the outer pins , beep is usually bad.

A part with "D" in it is a diode. Black prope on middle pin and red on either left/right pin. Beep is usually bad , depends on type and circuit.

[Dannyx]

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

You're saying you replaced IC1401. It's at this point that telling us what that chip is becomes necessary. Also, you found Q1601 shorted. Although less likely, when a FET shorts, it can also spit some voltage back into the control circuit via its gate pin which can kill other components there, especially since you tried putting in a new fuse when the FET was already shorted. Lesson learned: NEVER replace fuses after they blow without checking for shorts first.

I'd like you to measure the cathode side of D1250 on the right hand side of the board near the small transformer. It's what rectifies the AUX winding of the transformer and should output 20v according to the markings on the back. While you're doing this, it's also a good idea to measure other test points which are clearly labeled on the back, like HOT 20v or HOT 15v, though I believe you've already measured and reported 15v to be fine. Let me know how it goes and please provide us with the part number of IC1401 and preferably a schematic of the board if you have it (I believe you do so please share it) - a must for doing this sort of work. Cheers.

[budm]

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

Link to the schematic is in post #8.

[Dannyx]

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

Link to the schematic is in post #8.

Must've missed it amongst other posts

[Dannyx]

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

What's cool about this schematic is that they were also kind to mark what the voltage on each component is supposed to be, so you can easily probe around and see if the values match. Of course, you shouldn't try to measure high speed switching components like FETs and transformers because it's not only useless (a standard meter won't pick up anything), but might also result in blowing components. What's important at this point is to see if all ICs get their required VCC. The numbers in the schematic are VERY handy for this.

[dskall]

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

Not to good with schematics and haven't read all posts. Low 12vdc and 24vdc. I would check C1706, C1714 for capacitance and R1714. Someone correct me if not valid. Want to learn.

[Dannyx]

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

Not to good with schematics and haven't read all posts. Low 12vdc and 24vdc. I would check C1706, C1714 for capacitance and R1714. Someone correct me if not valid. Want to learn.

Precisely: learning is what this is all about. You say you're not too good with schematics, so perhaps that should be a place to start your quest for electronics knowledge I personally suck at math and formulas and sh!t, so I requested help here and there also. Anyway, don't want to digress from the task at hand which is fixing this PSU

[sfernandes]

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

You're saying you replaced IC1401. It's at this point that telling us what that chip is becomes necessary. Also, you found Q1601 shorted. Although less likely, when a FET shorts, it can also spit some voltage back into the control circuit via its gate pin which can kill other components there, especially since you tried putting in a new fuse when the FET was already shorted. Lesson learned: NEVER replace fuses after they blow without checking for shorts first.

I'd like you to measure the cathode side of D1250 on the right hand side of the board near the small transformer. It's what rectifies the AUX winding of the transformer and should output 20v according to the markings on the back. While you're doing this, it's also a good idea to measure other test points which are clearly labeled on the back, like HOT 20v or HOT 15v, though I believe you've already measured and reported 15v to be fine. Let me know how it goes and please provide us with the part number of IC1401 and preferably a schematic of the board if you have it (I believe you do so please share it) - a must for doing this sort of work. Cheers.

Yes i'll keep in mind for the future that when a fuse blows start looking for shorts before replacing the fuse.

The information on the IC is as follows...

Ref. No.: IC1401

Description: IC DUAL-PHASE PFC CONTROLLER HPA00651DR/SOIC

Part No.: NSCA0T0TY015

hope that helps. I will do the measurements you suggest above tonight or tomorrow and report back. I'm at work right now so I could not do the testing now. Thanks guys for all the help. I hope we get this thing going.

[Dannyx]

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

Yes i'll keep in mind for the future that when a fuse blows start looking for shorts before replacing the fuse.

The information on the IC is as follows...

Ref. No.: IC1401

Description: IC DUAL-PHASE PFC CONTROLLER HPA00651DR/SOIC

Part No.: NSCA0T0TY015

hope that helps. I will do the measurements you suggest above tonight or tomorrow and report back. I'm at work right now so I could not do the testing now. Thanks guys for all the help. I hope we get this thing going.

Thanks. I grabbed the schematic myself in the meantime thanks to BudM. The point is to make sure sure all the ICs receive their VCC correctly. The schematic is very handy in this respect because it instantly gives you the exact values your meter should read.

[sfernandes]

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

Thanks. I grabbed the schematic myself in the meantime thanks to BudM. The point is to make sure sure all the ICs receive their VCC correctly. The schematic is very handy in this respect because it instantly gives you the exact values your meter should read.

I understand, but I don't even know how to measure the IC's I was doing it then all of a sudden the fuse went and I swear i didn't jump my probes they are super sharp, i'm not sure what happened there, but glad I fixed it. But now i'm afraid to probe any other IC since I don't have tons of parts for this board so I can't be blowing things left and right lol. The way I did it the first time was the IC1401 was on the HOT side so I took the negative probe put it on the negative side of the big filter cap and was probing the IC1401 with the red probe pin by pin. I know the negative lead didn't slip off the negative of the filter cap because I used a small alligator clip to clip it onto the solder glob since it was big enough to clamp it there.

[Dannyx]

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

I understand, but I don't even know how to measure the IC's I was doing it then all of a sudden the fuse went and I swear i didn't jump my probes they are super sharp, i'm not sure what happened there, but glad I fixed it. But now i'm afraid to probe any other IC since I don't have tons of parts for this board so I can't be blowing things left and right lol. The way I did it the first time was the IC1401 was on the HOT side so I took the negative probe put it on the negative side of the big filter cap and was probing the IC1401 with the red probe pin by pin. I know the negative lead didn't slip off the negative of the filter cap because I used a small alligator clip to clip it onto the solder glob since it was big enough to clamp it there.

Since you were probing the PFC IC, it's no surprise one of the PFC transistors blew. You probably tried measuring one of the switching pins of the IC (that run the transistors) and that caused the pop...hard to say. Like I said, it's impossible to measure high speed switching signals with a DMM and trying it can have undesired results as you found out for yourself. I sure how nothing else got busted even further. You can however probe the VCC pins just fine. VCC is provided by the AUX winding (pin 10) of T1201. Since the transformer outputs AC, it needs to be rectified first, which is done by D1206 and D1250. Use your meter to probe their cathode side and compare your reading with the values printed in the schematic: should be 16-17v. Black probe on HOT GND and red probe on diode's striped side. You should see the correct values here, since you DO have standby voltage. Let us know how it goes and we'll push on.

[sfernandes]

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

Since you were probing the PFC IC, it's no surprise one of the PFC transistors blew. You probably tried measuring one of the switching pins of the IC (that run the transistors) and that caused the pop...hard to say. Like I said, it's impossible to measure high speed switching signals with a DMM and trying it can have undesired results as you found out for yourself. I sure how nothing else got busted even further. You can however probe the VCC pins just fine. VCC is provided by the AUX winding (pin 10) of T1201. Since the transformer outputs AC, it needs to be rectified first, which is done by D1206 and D1250. Use your meter to probe their cathode side and compare your reading with the values printed in the schematic: should be 16-17v. Black probe on HOT GND and red probe on diode's striped side. You should see the correct values here, since you DO have standby voltage. Let us know how it goes and we'll push on.

Just letting you know that I haven't given up on this. Stuff just came up and the weekend turned busy, but I will continue tomorrow and will do what was recommended above and report back my findings. Thank you

[sfernandes]

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

Since you were probing the PFC IC, it's no surprise one of the PFC transistors blew. You probably tried measuring one of the switching pins of the IC (that run the transistors) and that caused the pop...hard to say. Like I said, it's impossible to measure high speed switching signals with a DMM and trying it can have undesired results as you found out for yourself. I sure how nothing else got busted even further. You can however probe the VCC pins just fine. VCC is provided by the AUX winding (pin 10) of T1201. Since the transformer outputs AC, it needs to be rectified first, which is done by D1206 and D1250. Use your meter to probe their cathode side and compare your reading with the values printed in the schematic: should be 16-17v. Black probe on HOT GND and red probe on diode's striped side. You should see the correct values here, since you DO have standby voltage. Let us know how it goes and we'll push on.

Ok back at it. I probed D1206 and D1250.

D1206 = 15.74 Volts

D1250 = 15.90 Volts

How should I proceed next?

[sfernandes]

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

Any help is appreciated as I would like to continue with this tonight if possible.

[Dannyx]

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

I hope I (or someone else) will get back to you tomorrow, cuz I wanna friggin' go to bed, it's midnight here

[sfernandes]

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

I hope I (or someone else) will get back to you tomorrow, cuz I wanna friggin' go to bed, it's midnight here

Yikes lol I understand. Well could you help out tomorrow? If so I'll wait no problem.