EA261WM doesn't power on

[UpThyWazzoo]

Hello all, it's been a while since I started my other thread on the VX2450 (which I still haven't been able to fix, unfortunately).

I'm sitting on what appears to be an almost-new NEC EA261WM that doesn't power on.

>The button LEDs do not light. Using a no-power Samsung thread from earlier,

>I've measured the mains filter cap (165V)

>I've measured the 12V and 24V pin outputs. They not 0 with respect to ground, but they are in the low 100mV or less--which I assume is just as good as 0. This indicates to me that the power board is the culprit.

>I also found what appeared to be a burnt resistor at R994 (I've highlighted the location in the pictures). Interestingly, the voltage drop across the resistor was 0, but when I took it out to measure the resistance, it was 20 ohms. So now, I'm not really sure whether it was ever burnt to begin with. In any case, NEC support refused to clue me in to R994's value or give me a schematic.

Any ideas on what else I should be testing? Thanks in advance!

[PlainBill]

Re: EA261WM doesn't power on

This is a standard power supply design with an 'always on' standby supply, a main supply that is switched on as required, and a PFC front end. The resistor appears to be in the PFC circuit and could very well be the correct value. Check the datasheets for IC901, the PFC controller.

You mention a lack of 12V and 24V outputs. Unfortunately, the labels of the output connectors are obscured, so I can't see what the standby output voltage is supposed to be. It appears that the SMPS controller for the standby supply is IC905, bu I haven't mastered reading sideways. What is the part number of the 8 pin IC, IC905?

PlainBill

[UpThyWazzoo]

Re: EA261WM doesn't power on

Morning, Bill!

The part number is LD7522PS - 092855. Should I set about finding a 20 ohm resistor replacement?

[UpThyWazzoo]

Re: EA261WM doesn't power on

Here's a link to the part info: http://www.datasheetdir.com/LD7522PS+PWM-Controllers

With respect to Pin5:

Pin 1: 2.05V
Pin 2: 1.426V
Pin 3: 4.78V
Pin 4: 3.2mV
Pin 5: GND
Pin 6: 65.9mV
Pin 7: 16.9V
Pin 8: 0

[jetadm123]

Re: EA261WM doesn't power on

Many times a resistor will burn up because something else has shorted out. It looks like one side of R994 is connected to transistor Q902. Try checking Q902 for shorts.

[UpThyWazzoo]

Re: EA261WM doesn't power on

Q902 is an NPN transistor and it tested fine (19MOhm/Open, B-C, B-E) (Open/Open, C-E)

Also, IC901 is an [F] ek29 FAN7529. I believe this is the correct part: http://www.fairchildsemi.com/pf/FA/FAN7529.html

[PlainBill]

Re: EA261WM doesn't power on

Thanks for all the information and pictures. It's appreciated.

I'm not sure what the problem is. Start-up voltage for Vcc is 16V nominal, with a range of 15-17 volts. 16.9 volts is right at the ragged edge - it should be running, but the voltage you measured indicates there is no output. I don't think the problem is a shorted output diode. If that 16.9 volts was steady, the startup cap is not the problem.

At this point I suspect the LD7522PS. They are inexpensive enough, but the supplier I found wants about $8 for three of them (reasonable) plus $23 for shipping (outrageous)!!!

PlainBill

[UpThyWazzoo]

Re: EA261WM doesn't power on

In general, how close is that IC to being "the end" of the power board? Are there any ICs that are identical in operation but might be easier to find?

[jetadm123]

Re: EA261WM doesn't power on

Took a look at the datasheet for the LD7522. Looks like the Over Voltage Protection, OVP (pin 8) trips at approx. 2.5V. You're reading 4.78V. When the OVP trips, it shuts down the gate output (pin 6). Input to pin 8 is provided by either a zener diode OR two resistors. From your photo, it might be a zener. You'll have to verify.

[UpThyWazzoo]

Re: EA261WM doesn't power on

does this mean that the diode is shorting, or that something before the diode is putting out too many volts?

[jetadm123]

Re: EA261WM doesn't power on

If your setup is similar to the datasheet, then the supply voltage is the same as VCC (pin 7). A resistor network or zener would be used to set the voltage below the 2.5V threshold.

[PlainBill]

Re: EA261WM doesn't power on

Took a look at the datasheet for the LD7522. Looks like the Over Voltage Protection, OVP (pin 8) trips at approx. 2.5V. You're reading 4.78V. When the OVP trips, it shuts down the gate output (pin 6). Input to pin 8 is provided by either a zener diode OR two resistors. From your photo, it might be a zener. You'll have to verify.

Oops, I missed that. Good catch.

PlainBill

[UpThyWazzoo]

Re: EA261WM doesn't power on

I'm not totally up to speed on how to test a zener diode, but the voltage drop from one end to the other is 16.9V and -16.9V when I switch the leads. This actually seems normal. I read 4.78V on pin 3, and 0 on pin 8?

[PlainBill]

Re: EA261WM doesn't power on

Took a look at the datasheet for the LD7522. Looks like the Over Voltage Protection, OVP (pin 8) trips at approx. 2.5V. You're reading 4.78V. When the OVP trips, it shuts down the gate output (pin 6). Input to pin 8 is provided by either a zener diode OR two resistors. From your photo, it might be a zener. You'll have to verify.

Let's double check this. The OVP input is pin 8, which is at 0 volts. Pin 3 is the -latch input, and is the pin at 2.48 volts.

PlainBill

[UpThyWazzoo]

Re: EA261WM doesn't power on

How did you arrive at 2.48V? Did I measure something wrong

[jetadm123]

Re: EA261WM doesn't power on

Let's double check this. The OVP input is pin 8, which is at 0 volts. Pin 3 is the -latch input, and is the pin at 2.48 volts.

PlainBill

Thanks for checking PlainBill and my apologies to UpThyWazzoo for me not double checking my work.

[UpThyWazzoo]

Re: EA261WM doesn't power on

I doubled-checked my measurements, and they were accurate. What is the voltage on pin 1 being compared to?

[jetadm123]

Re: EA261WM doesn't power on

I doubled-checked my measurements, and they were accurate. What is the voltage on pin 1 being compared to?

If you look at the block diagram on the spec sheet, you will see that pin 1 (BNO) is being compared to a 1.25V threshold voltage. If the pin 1 voltage is lower than 1.25V, then the LD7522 shuts down. Since your measurement shows 2.05V, you're okay (see pin descriptions chart for pin 1).

[UpThyWazzoo]

Re: EA261WM doesn't power on

I see. The block diagram also shows the current sensing pin being compared to .85V? Could my reading of 3.2mV have any effect on that?

[PlainBill]

Re: EA261WM doesn't power on

I doubled-checked my measurements, and they were accurate. What is the voltage on pin 1 being compared to?

This is going to be a mess. The forum software does not support multiple spaces so I can arrange everything in neat columns, so I'll have to improvise.

Here are the results you got: (I took some liberties rounding numbers as required

Pin Actual / Normal / Function
1: 2.05V / >1.25V / Shuts down if Mains voltage too low
2: 1.42V / Varies / Regulates output voltage
3: 4.78V / <2.50V / Over temp protection
4: 3.2mV / <0.70V / Over current protection
5: GND 0 / 0V / Power supply ground.
6: 66 mV / > 1 volt-pulses / Drive to power FET
7: 16.9V / > 17V / Power supply
Pin 8: 0V / < 2.5V / Over voltage protection.

The only pin that is questionable is pin 7. The nominal startup voltage is 16 volts. The spec says it can start when Vcc is as low as 15V, and will start before Vcc hits 17V. Allowing for meter error, etc, it is JUST possible that Vcc is too low, so the LD7522 doesn't start.

At this time I see a few options, but don't have much confidence they will solve the problem.

1. Test all of the diodes in the area of the controller (in circuit) to see if any are shorted.

2. There is a resistor or series of resistors that drop the filtered mains voltage down to the 16.9 volts. Either my eyes or the picture resolution aren't good enough to allow me to locate it. Parallel it with a resistor that is at least 10X greater than the original.

3. Replace the startup capacitor.

4. Replace the SMPS controller.

5. Have someone brighter than me take a look at it.

PlainBill