bn44-00338b

[still4given]

Is there a schematic with voltage references somewhere for this power supply?
I have replaced the usual suspects but still no joy.

Thanks, Terry

[budm]

Re: bn44-00338b

What is it not doing?

[still4given]

Re: bn44-00338b

Thanks,

It is not powering up the TV. CM808 measured fine so I first replaced FSFR1700US. No improvement so I bought another as well as a new cap for CM808 and still not improvement. I read each thread about this SMPS but could not find the problem so I'm hoping to track down the problem by measuring voltages. If you have some specific things I could look for I would be happy to try them. I have quite a bit of experience building DIY amplifiers but I have not yet done much with SMPS other than buy them for use as a power supply.

Thanks, Terry

[still4given]

Re: bn44-00338b

Hi Bud,

I had a chance to look over the schematic but I don't see any voltage references. Can you give me some key nodes to measure that may help tracking down which part(s) may be failing?

Thanks, Terry

[budm]

Re: bn44-00338b

"It is not powering up the TV" No power indicator? no backlights?
First before trying to measure the voltage right at each section of each circuit, you should measure the voltage at each pins of the connectors between the power supply and the main board and between the power supply and the inverter board.
Do you have PS_ON and BL_ON from the main board? 5VSTBY is steady at 5V?
CM808 (0.015uF) which is connected in parallel with opto PC803S' Photo-transistor side, is that the one you replaced?
Are you not getting the 24V output? Is the PFC Voltage booster working. CM 801s (0.022uf 1000v) cap should be checked if you have ps_on, PFC Voltage booster.

[still4given]

Re: bn44-00338b

How do you measure each pin with the boards all plugged in? I had to have the bottom exposed to get to them. Can I test the PSU simply plugged in on the bench?

Thanks, Terry

[budm]

Re: bn44-00338b

You need sharp skinny probe. The power supply has pull-up resistor for the PS_ON so if you power up the power supply board by itself, it will force on the PFC Voltage booster circuit ( the DC Voltage at the main filter cap should be > 360VDC, and the 24V and the 13V should also come on.
BTW, when measure DC voltage on the primary side, the negative leg of the main filter cap is the GND ref point for the primary circuit. Chassis can be used for the GND ref for the secondary side of the circuit.

[still4given]

Re: bn44-00338b

DC voltage on the main cap is 160V. No 24V or 13V. 42V on the bridge.

[budm]

Re: bn44-00338b

"42V on the bridge" Which bridge? The output Voltage of the bridge BD801S will be pulsing DC because it has no large filter cap connected to the out put of the bridge, but we do have 160VDC on the main filter cap so the bridge is not the problem.
You measure 160VDC with no other board connected?
Check the DC Voltage on the PS_ON pin CN802 PIN 18 and the Ground pin 10 or 12 on the connector.
How about the 5V (A5V) STNDBY Voltage on pin 16 of CN802?

[still4given]

Re: bn44-00338b

Pin 18 has 0.723V and pin 16 has 5.28V. All other pins have 0.0v

Your right. I rechecked the bridge and it pulses on DC. The 42V was an AC measurement.

Yes, my measurements were with no other board connected. Taken on my bench with the board upside down so I could get to all the nodes.

Thanks, Terry

[budm]

Re: bn44-00338b

OK, now we need to find out if the PFC Controller IC (ICP801) is getting the VCC at pin 8, it should be around 15VDC, make sure to use negative leg of the main cap as the GND ref point.

[still4given]

Re: bn44-00338b

Pin 8 measures 14.91V

[budm]

Re: bn44-00338b

OK, the PFC IC Controller (FAN 7530) is getting the correct VCC to run, V start is 12V typ, so it is either the IC is bad or the MOSFET which is driven by the IC is bad, Diode DP802, or the Source resistor RP822 0.12 Ohms is open. You should also check the components connected to the Gate pin, check solder connections, etc.
Also take the resistance reading between GND pin of the IC against all other pins, make sure to report the readings if they are in Ohm, K Ohms, or M Ohm.

[still4given]

Re: bn44-00338b

IC referenced to pin 6
Pin 1 60k
Pin 2 47k7
Pin 3 inf
Pin 4 1R
Pin 5 20k
Pin 7 8k6
Pin 8 14m

DP802 checks fine
RP822 1m2

MOSFET checks OK with diode meter.

[budm]

Re: bn44-00338b

The resistance readings do not show any abnormal readings, at this point I would try new IC.

[still4given]

Re: bn44-00338b

Icp801?

[still4given]

Re: bn44-00338b

The resistance readings do not show any abnormal readings, at this point I would try new IC.

I sat down this morning and took some voltage readings of the IC and the MOSFET. I don't understand that circuit well enough to know what it is supposed to be doing so I am attaching them. Hopefully you can see where the problem is.

Thanks, Terry

[budm]

Re: bn44-00338b

As you can see, there is no Gate drive signal to the MOSFET, and the Drain Voltage is sitting at steady 160VDC. You should download the application notes of the IC to learn in details how PFC Voltage booster circuit works.

[still4given]

Re: bn44-00338b

Hi Bud,

Looking closer at the circuit made me suspect DP803. I'm not sure exactly how that diode is supposed to work but with my DMM on diode test I get 0.026V in both directions. Seems it ought to be open in at least one. That could explain the 4mv on pin 4.

[budm]

Re: bn44-00338b

As you can see in the diagram, the DP803 is connected in parallel with the 0.12 Ohms Source resistor so it will show very low resistance in both direction, to verify, you will have to lift up one leg of the diode and test it again, I doubt that it is bad.