Gateway FPD1975w SMPS

[alexanna]

This Monitor does not have any secondary voltages. And the power supply is different than other FPD1975w monitors
I measure 164v DC across the large capacitor.
The SMPS controller is an NPC1337.
There are two 25v 47UF capacitors in the area of the SMPS that have been replaced with Nichicon PW series.
The pin voltages of the NPC1337 are
1= .9v
2=0v
3=0v
4=0v
5=.2v
6=8v
8=25.5v
I am still not familiar with the start up process,But I feel pin # 1 may be a cause for concern.
I have attached a data sheet.
Al.

[jetadm123]

Re: Gateway FPD1975w SMPS

Replacing the 47uf startup caps eliminated one possible source of problems. Pin 6 is the VCC. The NCP1137 stays off at under 10V and starts at 12V. You have 8V. Pin 6 voltage is provided by a diode fed off the main transformer. Check this diode for a short. There may also be additional caps or resistors connected to pin 6 or the diode. Check these for shorts/proper values. Also check the mosfet on the heatsink above the large 450V cap for shorts.

[PlainBill]

Re: Gateway FPD1975w SMPS

And one point not yet mentioned, the NPC1337 may be bad.

PlainBill

[alexanna]

Re: Gateway FPD1975w SMPS

Ok this thing came back to life. It most likely was a poor solder joint on the SMPS coil although I did re solder other things on the hot side of the board.
Some of the voltages changed on the NPC1337
Pin 1 is now 1.09v
#2 is .13v
#6 is reading 11v
And pin #8 came up to 128v
I have not hooked up the logic board yet but I do have a good 5v going to the connector.
Looking at the rest of this power supply it's probably a good candidate for a lot of fresh solder.
Al.

[alexanna]

Re: Gateway FPD1975w SMPS

I spoke to soon on this monitor, after verifying I had a good 5 volts going to the logic board I did a total recap of the P/S inverter. Putting everything back together I had a really nice picture, and everything was working as it should. When I woke up this morning it is dead again.
I was really hoping I could boost my average of problems that I have posted in the forum,
I think so far I'm batting close to .000
Am I thinking correctly of a poor solder connection causing the problem?

[PlainBill]

Re: Gateway FPD1975w SMPS

I spoke to soon on this monitor, after verifying I had a good 5 volts going to the logic board I did a total recap of the P/S inverter. Putting everything back together I had a really nice picture, and everything was working as it should. When I woke up this morning it is dead again.
I was really hoping I could boost my average of problems that I have posted in the forum,
I think so far I'm batting close to .000
Am I thinking correctly of a poor solder connection causing the problem?

Poor solder, or a component overheating.

PlainBill

[alexanna]

Re: Gateway FPD1975w SMPS

There was a huge difference on pin #8,the high voltage pin.On the schematic of the NPC1337 it shows pin 8 being fed voltage through a resistor and the SMPS coil,with a Mosfet involved and through another resistor to pin 4 of NPC1337 which is a ground.
And I am guessing there are some diodes involved although it doesn't show them in the simple schematic.
Is that a good description of the circuit? Or is something else involved?
Al.

[PlainBill]

Re: Gateway FPD1975w SMPS

There was a huge difference on pin #8,the high voltage pin.On the schematic of the NPC1337 it shows pin 8 being fed voltage through a resistor and the SMPS coil,with a Mosfet involved and through another resistor to pin 4 of NPC1337 which is a ground.
And I am guessing there are some diodes involved although it doesn't show them in the simple schematic.
Is that a good description of the circuit? Or is something else involved?
Al.

The drawing in the datasheet is incomplete. Here's the usual design. The rectified line voltage goes to pin 8 of the IC. There is a filter cap connected to pin 6. The IC contains a constant current regulator which charges the cap from the rectified line voltage. When the voltage at pin 6 reaches about 12 volts the SMPS controller starts driving the gate of the FET. It also turns off the constant current regulator, as a result the voltage at pin 8 will rise. The FET of course drives the primary of the transformer; secondary windings are rectified to produce the output voltages, typically 5V and 12V. The 5V output is monitored and fed back to the SMPS controller through the opto-isolator to maintain a constant 5V at the output.

There is a tertiary winding on the transformer that is connected to pin 6 through a diode and sometimes a resistor. That provides the run power for the IC.

PlainBill

[alexanna]

Re: Gateway FPD1975w SMPS

Well my hair has developed a lot more gray ones; I know this should be very simple.
This has failed in a different way there is only 180MV showing on pin 6 of the NPC1337
What I have found is pin 6 of the NPC1337 is grounded. If I place the red lead of the DMM on the positive lead of the large cap I am reading 164VDC with the negative of the DMM hooked to pin 6 of the NPC1337.The small 25v 47uf cap is not shorted and there are some poly caps that appear to be in the circuit also, these are not shorted. So I don’t think that pin 6 should be grounded.
If I check resistance of pin 4 to pin 6 I am reading 380 ohms.

[PlainBill]

Re: Gateway FPD1975w SMPS

Well my hair has developed a lot more gray ones; I know this should be very simple.
This has failed in a different way there is only 180MV showing on pin 6 of the NPC1337
What I have found is pin 6 of the NPC1337 is grounded. If I place the red lead of the DMM on the positive lead of the large cap I am reading 164VDC with the negative of the DMM hooked to pin 6 of the NPC1337.The small 25v 47uf cap is not shorted and there are some poly caps that appear to be in the circuit also, these are not shorted. So I don't think that pin 6 should be grounded.
If I check resistance of pin 4 to pin 6 I am reading 380 ohms.

D804 is the diode for Vcc. C807, C810, R813, and IC 801 are other possible suspects.

PlainBill

[alexanna]

Re: Gateway FPD1975w SMPS

D804 is the diode for Vcc. C807, C810, R813, and IC 801 are other possible suspects.

PlainBill

Thanks PlainBill,I had found all the components except IC801 octocoupler.Removing it from the circuit causes the resistance of pins 4 and 6 to increase to about 1.5K ohms.
I am unable to prove IC 801 shorted with an ohmmeter test. If I use the diode function I read 1.04v on pins 1 and 2,pins 3and 4 show open.
I have enough spare parts around here I should be able to find another one to substitute and see if it makes a difference.
Al.

[alexanna]

Re: Gateway FPD1975w SMPS

Replacing the octocoupler with a new one, I have very high resistance between pins 4 and 6 of the NCP1337.Upon Appling power to the circuit I still have very low voltage on pin 6, and it is still indicating that pin 6 is grounded when voltage is checked with the positive lead of the large capacitor.
Is there anything else I can check, or is it time to replace the NPC1337?
Al.

[PlainBill]

Re: Gateway FPD1975w SMPS

Replacing the octocoupler with a new one, I have very high resistance between pins 4 and 6 of the NCP1337.Upon Appling power to the circuit I still have very low voltage on pin 6, and it is still indicating that pin 6 is grounded when voltage is checked with the positive lead of the large capacitor.
Is there anything else I can check, or is it time to replace the NPC1337?
Al.

I'd replace the NCP1337. This design frequently fails. You HAVE verified the diodes on the secondary are not shorted, haven't you?

PlainBill

[alexanna]

Re: Gateway FPD1975w SMPS

I'd replace the NCP1337. This design frequently fails. You HAVE verified the diodes on the secondary are not shorted, haven't you?

PlainBill

The schotty barrier diodes have been removed from the circuit and tested; they are not showing short with ohmmeter. Diode testing they are showing a voltage drop of .145v on the 40a and .225v on the 100a one.
Question to be sure something weird is not happening, could I safely apply power to the board with these diodes removed from the circuit,and see if anything changes on pin6 of the NPC1337?
Al.

[alexanna]

Re: Gateway FPD1975w SMPS

^Typo on diode amprege 10a 40v and 10a 100v is corect

[PlainBill]

Re: Gateway FPD1975w SMPS

The schotty barrier diodes have been removed from the circuit and tested; they are not showing short with ohmmeter. Diode testing they are showing a voltage drop of .145v on the 40a and .225v on the 100a one.
Question to be sure something weird is not happening, could I safely apply power to the board with these diodes removed from the circuit,and see if anything changes on pin6 of the NPC1337?
Al.

Ordinarily I would say no. The SMPS controller will keep increasing the drive pulse duration to the fet until something overloads. In this case, the smps controller shuts down if Vcc rises above 17 volts. It may not tell you much, but you can.

HOWEVER, I would suggest you reinstall the schottky diode for the 5 Volt supply and test it that way.

PlainBill

[alexanna]

Re: Gateway FPD1975w SMPS

Ordinarily I would say no. The SMPS controller will keep increasing the drive pulse duration to the fet until something overloads. In this case, the smps controller shuts down if Vcc rises above 17 volts. It may not tell you much, but you can.

HOWEVER, I would suggest you reinstall the schottky diode for the 5 Volt supply and test it that way.

PlainBill

I replaced the schottky’s from I used board I had, to rule them out as being a problem.
The voltage stays very low on pin on pin 6 of the NPC1337, I guess it’s time to source a controller.
Thanks for the help, I will update when I find the part

[alexanna]

Re: Gateway FPD1975w SMPS

I received the NPC1337 yesterday and while I was installing it, I removed this resistor to make sure I did not create a solder bridge. Its colors are Brown- Black-Black it is tied to pin 5 of the NPC1337 and then the circuit goes to a schottky diode. The resistor disintegrated removing it. I know it's 10 ohms,but would this be a metal oxide resistor?