MPF6908 No 5V on pin 6 to A Board

[LITEZONER]

hello all, need some help with this issue TV Model is TC-50PX34 Manufactured in 2011, this unit used the Power supply MPF6908 stock image included, My issue is dead, no power, no standby lights, nothing, No click and powering up power supply, no 5V out to pin 6 of the A board. Took some readings and only getting 1.2V AC into the bridge rectifier, any help on where to test next would be very helpful, Thank you very much .

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

another picture

[dick_barton]

Re: MPF6908 No 5V on pin 6 to A Board

Have you checked both fuses?

[R_J]

Re: MPF6908 No 5V on pin 6 to A Board

I would check the fuses and then check the standby circuit, thats where your standby voltage comes from, if you post a good picture of the back of the board that would help in troubleshooting

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

Thank you, fuses are good, here is some pictures of the back of the board

[dick_barton]

Re: MPF6908 No 5V on pin 6 to A Board

I see there is a ceramic resistor (tall white). Have you checked that. If the fuses are not blown then there is every likelihood you have an open circuit somewhere along the path from the mains input connector to the bridge rectifier. The dc voltage written on the side of the capacitors is a good indication of what voltage you should read across it.

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

checked that 10 Ohm resistor tested good, so plug it in and test the voltage across the 4 caps (black rectangle plastic) ? The schematic is annoying or I am just not up to par on reading it, the numbers on the board do not correspond to the numbers in the schematic at all, also i believe i found what i think is several what i think are Zener diodes that measure both ways, if i am not mistaken they are the small peach colored diodes with a white stripe. check out this schematic, it doesn't give values only proprietary part numbers, and again the location does not line up with the numbers on the board. also it is barely legible in the block diagrams

[dick_barton]

Re: MPF6908 No 5V on pin 6 to A Board

I cannot see a reason then why you do not have a reasonable AC voltage across two legs of the bridge rectifier. Have you measured the voltage with the meter set to ac range with the meter probes on the ~ symbols (of the rectifier) and next measure the dc voltage with the meter set to dc with the probes on the bridge rec terminals marked with the + and - symbols.

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

Me neither, has to be either the wire wound Transformer or one of the varisistors I'm guessing. anyone who wants to chime in?, Incidentally i did find a blown fuse, I see now that it is blowing the outer most fuse when i power it on, that condition must have been present when i posted this issue.

[budm]

Re: MPF6908 No 5V on pin 6 to A Board

You are not not going to get any AC at the two inner pin of the main bridge until the main board sends out the relay signal to turn on the power relay RL001, 002.
The STBY SMPS is running off the half wave rectifier D006 (WHEN tv IS IN STANDBY MODE), the B+ output (Cathode) is fed through the Thermistor NTC001, the out put of the thermistor is then feed the filter cap C102, so you should have about 160`170VDC bteween the two legs of the C102.
SMSP IC101 is for driving the power MOSFET Q101 which drives the standby power supply transformer T101 primary winding pin 5 & 6.
You need to check the fusible resistor R112, 125, 126. Check thermsitor NTC001 and the D006 if you do not have DCV on C102.
BTW: Incidentally i did find a blown fuse, I see now that it is blowing the outer most fuse when i power it on, that condition must have been present when i posted this issue. You mean the 6.3A main fuse is blown the minute you apply the AC to the board?If that is the case, then you need to check the resistance of the MOV Z001, 002, and 003.
Pictures are provided by SHOPJIMMY.

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

these 3 MOV or varisistors? Thank you very much for the information.

[budm]

Re: MPF6908 No 5V on pin 6 to A Board

They are MOVs which are the same as Varsitors.
the key point is that if you just power up the power supply board by itself without having other boards connected, it should not blow the fuse.

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

hey, thank you, is the red one NTC001 a varisistor as well?

[budm]

Re: MPF6908 No 5V on pin 6 to A Board

NTC001 is not MOV, it is Thermistor (it is used for inrush current limiting) which should show low resistance, if it shows open circuit then it is bad.
So is the fuse still blowing?

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

I need to look up how to test these items, I replaced D006 with a rectifier diode, Not half wave, and replaced NTC001 after it blew up with ZNR V14621U also need to try and find part numbers that are not proprietary on these.

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

I believe the NTC001 is a 600V MOV?

[budm]

Re: MPF6908 No 5V on pin 6 to A Board

Doo6 is setup as half wave rectifier circuit, full wave will be more than one diode.
"ZNR V14621U" Where is this part? it is not shown in the circuit for the STBY SMPS section.
NTC is NOT MOV, it is connected in series with the load, MOV is connected in parallel with the laod, completely different function from NTC.
How what resistance did you get on the NTC?

http://www.ametherm.com/inrush-current/

MOV (VARISTOR):
http://www.littelfuse.com/varistor
Half wave rectification:
http://www.electronics-tutorials.ws/diode/diode_5.html

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board

shows open no resistance. NTC001 do you know what the correct part number is for the NTC? this part was used to replace NTC ZNR V14621U

[LITEZONER]

Re: MPF6908 No 5V on pin 6 to A Board



ERZV10D621 Varistors 620V 2500A ZNR SUR ABSORBER 10MM

[budm]

Re: MPF6908 No 5V on pin 6 to A Board

Since NTC is in series with the load, so if the load, in this case that will be the MOSFET that drive the power transformer will be the first suspect, is shorted out then the NTC will blow up.
Where did you get the 'ZNR V14621U' from? Was it printed on the body of the NTC001?
That ZNR is NOT NTC, it is MOV (vARISTOR, SURGE SUPRESSOR).
As you can see how the desinator for the component are.
Z001 for the MOV (Varistor, surge suppressor). bad MOV will show really LOW RESISTANCE, good MOV will show very very high resistance (open circuit).
NTC001 = NTC for inrush protection.
Look at the conection, the CATHODE of D006 is connected to the one leg of the NTC001, the output leg of the NTC001 is connected to filter cap C102 positive leg. which is connected to the Transformer pin 6 primary winding.
I do not believe you are understanding how the circuit functions and how the components are used in the circuit.
They do not put MOV in series with the load.