A1466 820-000165-A with low PP3v42

[mon2]

Re: A1466 820-000165-A with low PP3v42

Yes.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

The results are the almost same. The voltage at L7095 is 0.270V.

[mon2]

Re: A1466 820-000165-A with low PP3v42

What is the input voltage on pin #6 of this regulator?

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

HI mon2,

It is 14.3V.

[mon2]

Re: A1466 820-000165-A with low PP3v42

Reflow the regulator chip. Use flux.

[mon2]

Re: A1466 820-000165-A with low PP3v42

Also, remove all power. Meter in resistance mode.

Check the resistance to ground of this output inductor.

If there is no short or low resistance then review the resistance of the feedback resistors on this regulator. Do not, repeat do not remove the resistors but check their values. These resistors will define the output voltage.

Do the measurements of the resistors match the schematic values?

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

R7080 was missing on the mobo. Replaced it. The voltage has come up to 3.371V which is not near to the ideal 3.425V. I am yet to check the other resistors.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

R7096 - 143.1 kohms
R7095 - 163.5 kohms

The resistance to gnd on output of L7095 is cycling from 3.3 KOhms to 2.6 Mohms and over again. What could be happening? The only component off the board is C7090.

[mon2]

Re: A1466 820-000165-A with low PP3v42

Remove all power. Apply flux and remove r7095 or slightly shift the part with low air pressure so it is one one pad only. Do not lose the part. Measure it's resistance. Use low air pressure!

Then repeat to test R7096.

See the formula on how the resistors affect the Vout.

Vout = 1.25V * (1 + Ra / Rb)

If these resistors are lost, do not power up else the Vout will spike and the board will be killed.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

The resistance to gnd on output of L7095 is cycling from 3.3 KOhms to 2.6 Mohms and over again. What could be happening? The only component off the board is C7090.

[mon2]

Re: A1466 820-000165-A with low PP3v42

Do not worry about this swing. Assorted components will charge and discharge during the resistance checks and impact the final value.

The key point is that this resistance is not considered to be low. The max current out of this regulator is 300mA so it cannot support a very low resistance of a load at the output.

Focus on the feedback resistor values. Be sure their values make sense so best to remove and check each when they are out of circuit. Do the check one part at a time. If out of range, they will affect the output voltage.

Again, double check that both are not removed after this work else the board will be killed.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Here are the reading of R7095 & R7096 after being disconnected.

R7096 - 202 KOHMS
R7095 - 347 KOHMS

[mon2]

Re: A1466 820-000165-A with low PP3v42

What is the resistance to ground at L7095, pin #2 ?

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

The resistance to gnd on output of L7095 is cycling from 3.3 KOhms to 2.6 Mohms and over again. What could be happening? The only component off the board is C7090.

[mon2]

Re: A1466 820-000165-A with low PP3v42

So output is not shorted.

Most regulators have a minimum input capacitance requirement for stability of the regulator.

Check if the voltage to ground is stable at the input pin #6 of this regulator.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

The voltage at pin 6 of U7090 is 14.02V and is stable.

[mon2]

Re: A1466 820-000165-A with low PP3v42

Suggest to purchase fresh resistors @ 1% tolerance or to remove from a donor board for testing.

R7096 - 202 KOHMS
R7095 - 347 KOHMS

Replace the FB resistors @ R7095 & R7096.

With the measured values, the

Vout = 1.25V * (1 + Ra / Rb)
= 1.25V * (1+347/202)

Vout = 3.397 volts.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

I do not have any donors lying around. When it comes to buying it, the tolerance i can get hold of is 5%. can it be used?

[mon2]

Re: A1466 820-000165-A with low PP3v42

It is best to purchase 1% tolerance - it should be available in your local markets but 5% will have to do as a backup.

Purchase the values noted in the schematic and then test again. Measure the resistor value before stuffing onto your PCB.

If you stuff the values shown in the schematic into the equation, the Vout should be 3v42.

[piernov]

Re: A1466 820-000165-A with low PP3v42

5% tolerance will obviously make it worse. 0.05V difference isn't a lot, that said PP3V42_G3H is indeed more accurate than this usually but probably not worth adjusting feedback for that.