PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Ok some good news and bad and some confusion. I tried doing the figure 17 test procedure and it was getting me nowhere. So after some time it dawned on me i never hear any clicks of the relays. I check the relay plug 1306 all 3 pins have 5 volts, ok so why am i not hearing any clicks? I take the cover off the relay confirm it is indeed not energized. ok so i took a risky move and manually engage it and there is 2 relays on the power board so i only energized half of the power board i presume..., and blew the fuse 1U04 it's for +12vsw on main board DARN IT!!!!!


So after thinking ok so if i manually engage it, and obviously it brings something to life albeit did not want to blow fuse on main board. And then i question why the relay is not working like it should. Take the power board out looked that section over and it seems to be ok. Took a 9 volt battery and pig tailed to connector 1305 on my desk and it clicked and worked WTH? and looked at schematic and then i found it says pin 3 will go low when tv turns on, ok so i remember pin 3 never went low but confused as to why i can get it to work with 9 volt battery.


So i put the power board back into the tv and disconnected the main board completely to prevent any more possible damage.

Connected everything else including standby board. but i left the relay plug unplugged and pig tailed the 9 volt battery to the relay again. and BAM backlights turn on to my shock. OK cool i said progress!!! so lets get some voltage readings...

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Readings as follows::::::::::::::::::::::

1J02 this plug splits into 2 plugs for the standby board 1M46 & 1M03 i took readings at the end and is disconnected from main board

pin1::: N/A
pin2::: N/A
pin3::: N/A
pin4::: 5.2v
pin5::: 0v supposed to be 5v maybe generated on main? main disconnected
pin6::: 0v
pin7::: 0v
pin8::: 0v
pin9::: 11.8 to 11.9
pin10:: 11.8 to 11.9
pin11:: 0v did have 3.4v assuming it's generated on main
pin12:: 2.9v confused to how it's doing this without main for backlght control
pin13:: 1.5v lamp on signal, again doing it without main



Now to power supply main

1306 plug is getting 147.8v supposed to be 160v but working anyhow it's main feed to standby board


1M02 this is for audio output to main board but is disconnected from main board

pin1:: -20.7 supposed to be -18.3 maybe it needs a load? as in connected?
pin2:: -20.7 supposed to be -18.3
pin3:: 0v
pin4:: 0v
pin5:: 19v reading calls for 18.3
pin6:: 19v calls for 18.3
pin7:: 0v


1304 output plug on main power supply to standby board input

pin1::21.2v reading calls for 24v
pin2::21.2v calls for 24v
pin3::11.8 to 11.9
pin4:: 11.8 to 11.9



1303 Cannot find any info on this plug in schematic whatsoever but it does need it and it's the only black plug the rest are white have no idea what the spec is supposed to be and it is connected from main power board to standby board and plugs right next to 1304 on standby board.

pin1:: 24.5v
pin2:: 24.5v
pin3:: 0v
pin4:: 0v


And remember the back light was on entire time taking voltage readings. So now anything look really bad here? I feel it may be ok.

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Now i reconnect main board and returned everything the way it was no forcing power board on, and 6 blink error code is still there with the blown fuse in it, but i remember checking that fuse before it blew and it never had and voltage readings at that point apparently only when i force power supply on obviously because that is when it blew so i am thinking there might be a problem on the dc to dc converter section on that board i will check around and update what i find er don't find. also forgot to mention 1J02 plug supplies 12 volts on pins 9 and 10 i did not put that on my homemade drawing schematic. And we need that for activate the mosfet to turn on 5 volts and when i bypassed it and jumped the 5 volts over earlier in this thread it changed the error from 6 to 12 missing 12 volts.... At this point i am guessing there is a short somewhere in the 12 volt section on main board i will check around later today i need to get to bed it's 4:30 am LOL man i am trying like heck to get this figured out and see what i find and if you have any suggestions please indulge thanks again for sticking it out with me....

[RON_CET]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

sounds like your heading the correct path and your troubleshooting steps look good

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Well looked around dc-dc converter section and no voltage going to the 7U00 and no shorts that i can see, i am stumped ATM...if i supply 12 volts it blows the 1U04 fuse, looks like the 5 volt and 12 volt is supposed to come on at same time????? We know we have 5 volts at 7U25 but it needs to dump to it's gate from 7U24, appears to need 12 volts to make that section work but if i supply 12 volts it blows fuse.



Now if i jump 5 volts it changes there error from 6 to 12.
so from 5 volt error to 12 volt error i am confused.


What am i overlooking? Something is telling the main power supply to turn on for obvious reason it will blow the 1U04 fuse. So where do i check now? Am i safe saying the problem is all in the main board or there still could be something in standby board that may not be cooperating with main board?

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Note 1: If fuse 1U01 is broken, this usually means a pair of
defective power MOSFETs (7U01 or 7U03). Item 7U00 should
be replaced as well in this case.


Found this in the other repair manual. Not the training guide so i guess when i added 12 volts and it turned on 7U25 and turned on dc-dc converter one of the mosfets has a short and blew fuse 1U01 sound about right ?

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Anybody want to teach me how to manually test 4936A SOT-8 dual gate transistor mosfet? Since i am not getting voltage to that part of circuit i would like to verify that it is indeed bad... Thanks i would like to be for sure or point me so a resource that will? It is different then a linear mosfet and i tried finding resources for testing that specific style mosfet and no luck. and not good at cross referencing compatible parts any secrets to that? I want to attempt to repair the main board. I am very Leary of buying used main boards on ebay and shop jimmy has none. Maybe somebody has a trusted seller on there? I would rather fix the board and know it's gonna work before a guessing game replacing mosfet is gonna work or not, and if i get a bad board from ebay who is to say it won't do the same thing later on provided it does not come DOA with the exact same problem which i have had happen from buying used boards on eBay and it's a real hassle even when the seller had good ratings.. Besides i if i can help it i would rather replace if it is indeed bad, with a higher quality part that is compatible... I am still a bit green. I have learned a lot from here but have a ways to go yet. Especially compared to the legends on here. Thanks in advance.



P.S. I already removed them from board , soldiering skills getting better every time i soldier , i have a decent X-Tronic rework/soldering station 4000 series surprisingly works very good and makes the job much easier then a radio shack iron...

[RON_CET]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

you can test out of circuit with similar hookup to circuit in set with pins 5678 @ 5 volt supply voltage pins 2/4 hooked to variable dc supply pins 1/3 to load source then run you variable dc up on pins 2/4 once you get above the breakover voltage which would be above your drain supply voltage then you would see output at your source.NOTE your are referring to 7u25?

mouser has these http://www.mouser.com/ProductDetail/...9O8gPDPreyc%3d

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

7U25 is the same as 7U01 and 7U03 all 3 are 4936A SOT-8 dual gate transistor mosfet. 7U01 and 7U03 are in the dc-dc converter section and in repair manual it said if fuse 1U01 blows check 7U01&7U03, and if bad replace and should replace 7U00 at same time, fuse blew when i supplied 12 volts when i forced power supply on.


And before i forced power supply on it had 5 volts sitting there at 7U25 and when i jumped 5 volts over it changed the error code from 6 blinks to 12 blinks. So in theory when i supplied the 12 volts it needed to make 7U24 to function it blew fuse. So maybe the dc-dc converter section was the culprit. Perhaps there is an error in the software checking for 5 volts before checking 12 when it should check for 12 first before the 5 volts because it needs the 12 to make the 5 work in theory.... And 12 volts also goes to that section of the dc-dc converter section...


I do have some concerns that i hope i did not damage the standby processor or anything further down the line but have some doubt it did because even with fuse blown it still gives that annoying 6 blink error. And before the fuse blew it never had voltage to that section just 5 volts, only when i supplied the 12 when it went pop.....

But to make sure my theory is correct i want to verify& test before ordering anything.... and if i do order those mofets i might as well replace all 3 and the 7U00 that the manual recommends.... it is shutting off power supply for some reason(Well 5v and 12v after you supply the 5v it throws a different error) Am i making any sense or do i sound clueless? LOL. Still learning . Thanks for your reply and how to go about testing these mosfets. Could you check the schematics and verify if my theory is possible?. I am still learning symbols, and how different circuit section functions. like i just researched on dc to dc converters first time i had to deal with that type etc...

Added::::
I don't have a variable dc supply, Will a 5 volt wall wart work? Someday i will get one if i keep attempting to fix broken things but budget is tight....

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Any remarks for the questions? will a 5 volt wall wart work to test mosfet? or do i have to have a variable supply? thanks

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

or at least rig something with normal household items to perform test? i do have some spare boards to salvage something to make a test jig of some sort?

[RON_CET]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

I personally have only used variable dc supplies when I'm applying gate or base voltages to a solid state device which allows not only to bring up the operation of the device slowly but also allows me monitor current drain also,but you can try your wall wart but the gate voltage must be higher than you drain source to make the junction conduct.

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Thanks for key info i will try that and post results....

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Can anybody help me find a suitable replacement for PHD38N02LT cross referencing wise? That is still available @ digikey? or ebay? Been hunting and not sure what would work. it goes to 7U28 on main board. I added the datasheet for specs to compare to original against a suitable replacement i hope. It's part of the 2.5 volt stabilizer for the dc-dc converter. It measures open on DMM no matter how you go about it but appears to be physically OK in appearance...

[RON_CET]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

the Philips part# 934057587118 which not many vendors have or this eBay replacement might work

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Okay the main board is not the problem i ordered a brand new one and installed it and same error 6 blinks , when i forced it on last time i blew the rectifier and fuse on the old main board. So we are looking in the wrong place. I am miffed ATM... what else could be causing 5 volt error?

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Any ideas anybody? if you disconnect main board completely which i learned the hard way BTW and been disconnected ever since when i force the tv to turn on with a 9 volt battery to the relays back lights and everything will turn on just no picture obviously because main is disconnected, reconnect everything the way it supposed to be with new board which i found barely i still get 6 blink 5 volt error, the original main got zapped due to learning the hard way when you force it on it blew the rectifier and fuse on the original main board, and i did not want to gamble replacing the rectifier which is just about impossible to find due to being obsolete part so i just went ahead and got a new one well now i am back to where i was just blinking 6 error missing 5 volts, is there something in the standby board even though it appears to work when forced without main connected but anyhow is there something there in standby that could be the reason 5 volt is not reading er working.

Not real good at schematics yet so can anybody steer me in the right direction perhaps or is it a lost cause? which i doubt. Thanks i really need to get this thing out of my hair......Budm? ron-cet? perhaps tom66 even though he mainly works with plasma tv's .....

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Bump

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Could i have been sent another bunk main?

[heavymachines]

Re: PHILIPS 42PF7421D/37 Chassis EL1.1 U AA

Ok may i ask did i offend anybody somehow? anybody decent enough to answer this question... Being judged? Not sure why everybody is silent on this.