MPF6908 No 5V on pin 6 to A Board

[budm]

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

I am so sorry, i am getting 165DCV Across C102, I am an idiot I had my meter on incorrect range, i am going to go stick my tongue in a light socket for punishment.

Good. we do have DCV to power the STBY power supply circuit, but still no STBY DC on the output side.
So it is either the SMPS IC that drive the Power MOSFET is bad, the Source resistor R112 is open, the startup/running filter cap C117? (NEXT to the R112) is bad. I forget the P/N of that SMPS ic.

[LITEZONER]

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

Next thing is IC101? 5528 or 2A10917 these are the numbers at IC101

[LITEZONER]

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

R112 is closed, the startup/running filter cap C117? I get 10-12 volts across here, I don'y own an esr meter to check the cap the right way.

[budm]

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

Fa5528.
You need to check the resistance between GND pin 4 against all other pins to see what you get and report the reading.
Then you will take the DCV reding between GND Ppin 4 and the VCC pin 6 to see what you get.
the IC needs VCC 15VDC typ Voltage for it to start (range is 13.2~16.8VDC).

[budm]

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

Dam! BC site is really bad today.

[budm]

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

R112 is closed, the startup/running filter cap C117? I get 10-12 volts across here, I don'y own an esr meter to check the cap the right way.

Too low to start, see post 44.

[LITEZONER]

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

the voltages are extremely eradic on all pins from ground, ranging from .80 to 17V and jumping all over in between there

[LITEZONER]

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

pin 4 to 6 10 to 13V jumping all over in between, I am going to go ahead and order this part, Thank you very much for taking your time to help me on this being a holiday weekend budm, I know were not done, but i will pay it forward someday. Have a great weekend, or if you are not doing a dam thing like me, i'll talk at you later, Thanks again.

[budm]

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

the voltages are extremely eradic on all pins from ground, ranging from .80 to 17V and jumping all over in between there

That means it is trying to run, so it can be due to bad start up cap, or there is problem in the secondary side so it is in start/stop mode. I would verify that the rectifier in the secondary side are good, you also try putting in new start up/running cap.

[LITEZONER]

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

start up running cap is C117 and do you mean the full wave rectifier diode in the secondary?

[LITEZONER]

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

just checking specs on C117 and saw diode at D104, shows closed circuit both ways. R112 was hiding it near the heat sink

[budm]

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

Secondary side: There are two rectifier D501 (SMD) and the Dual Common Catode D151 mounted on the heatsink.
D104 is connected in parallel with the LOW Ohms Source resistor R112 (< 1 Ohms resistor) of the power MOSFET, that is why you are seeing conduction in both directions due to the resistor.

[LITEZONER]

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

Okay, i'm going to have to put a pin in this for now, i cannot see straight. Thanks again for all your help, will pick this up soon.

[LITEZONER]

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

found the cathode D151 on the heatsink, cannot seem to locate this D501 (SMD) there are 2 of them? SMD has to be on the bottom and only on the secondary side, it just seems invisible to me, There is a D551 on the Heatsink? but it's not SMD so that can't be it. I will keep looking for D501 SMD

Secondary side: There are two rectifier D501 (SMD) and the Dual Common Catode D151 mounted on the heatsink.
D104 is connected in parallel with the LOW Ohms Source resistor R112 (< 1 Ohms resistor) of the power MOSFET, that is why you are seeing conduction in both directions due to the resistor.

[budm]

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

https://www.badcaps.net/forum/showpo...8&postcount=10
I see the SMD in the pictures in the link.
D151 is will be the one that's more likely to go bad than the SMD one.

[LITEZONER]

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

Okay, Schottky barrier diode,YG862C15R. Neg lead on center pin Pos lead to pins 1 and 3 I get 223 I reverse the leads to Pos on center pin (pin 2 and neg lead on pins 1 and 3 I am getting 6 to start climbing to 18 then going to open circuit. (This seems correct) 3rd test, neg lead on pin 1 and pos on pin 3 closed circuit, and same way reversed. (This also seems correct)

[budm]

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

It is good, not shorted out.

[LITEZONER]

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

Okay, I just need to find the elusive (Bigfoot) D501 SMD, it seems to me all the SMD's on this board start with IC, or Q prefix, But i will keep looking, maybe give it someone here for a fresh set of eyeballs on it.

[LITEZONER]

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

Hello Budm if you are seeing a D501 anywhere on this board could you please tell me what it is next to? I have studied this board for over 30 minutes on the secondary side and cannot seem to locate it to save my life. Thank you

Okay after handing to two others i am convinced there is not a D501 on this board.

[budm]

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

https://www.badcaps.net/forum/attach...5&d=1441333829
It is just the above the label 'COLD' on the left side of T101 STBY xformer.