A1466 820-000165-A with low PP3v42

[bridges_4u]

Hi,

I have got an 820-000165-A motherboard which has got a strange problem. I have 14.32 V at R7005. But when i check pin2 of D7005, it says 0.9V. The diode is OK. Tried changing U7090 too. Any clues?

[mon2]

Re: A1466 820-000165-A with low PP3v42

Remove all power. Meter in resistance mode.

Check the resistance across R7005. Is it ~10 ohms and stable?

Sounds like R7005 is defective or power path is broken.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

I am happy that I got to talk to you again. I have continuity between pin 2 of D7005 and R7005. Yep. The value of R7005 is 10 Ohms.

[mon2]

Re: A1466 820-000165-A with low PP3v42

Remove d7005. Measure the voltage again at pcb pad #2 of the removed d7005 diode.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

It is 0.9V.

[mon2]

Re: A1466 820-000165-A with low PP3v42

R7005 is defective. Replace it and then check the voltage to ground again at pin #2 of the D7005 PCB pad.

Do not solder back D7005 till this voltage returns to be the same as the voltage into R7005.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

I replaced R7005. Now I get 14.2v at D7005. But when I check L7095 it shows only 0.160v instead of 3.425v. There is no short on ground at either side of L7095. On pin2 of U7090 i get 0.160v. I replaced u7090 twice, same results.

[mon2]

Re: A1466 820-000165-A with low PP3v42

The fault is (common) and at the input side of U7090. Very likely you have a shorted capacitor which killed the diode / R7005 network.

1) Check the voltage at the input of this regulator (Pin # 6) of U7090.

2) Remove all power -> meter in resistance mode -> check the resistance to ground of pin #6 on U7090.

Likely the input bulk cap is defective and causing a short circuit. Review the input caps.

Remove each till the short is gone.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

Sure. Will do. Moreover, I had voltage fluctuating at L7095 before this occurred. Can u suggest as to why that could have happened.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

When i try to check the resistance to gnd on pin6 of U7090, it is jumping all over the place. It initially shows Mohms, moves down to KOhms, and then Ohms. Then cycles all the way back. Would that be due to the shorted caps?

[mon2]

Re: A1466 820-000165-A with low PP3v42

Yes.

Remove each of the 3 caps and confirm that the resistance is stable. Someone is shorted inside this group of parts.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

After all the caps, when checking the resistance to gnd, it is fluctuating between kOhms and Mohms steadily. Once i put in only C7090, it fluctuates between all the way like before.

[mon2]

Re: A1466 820-000165-A with low PP3v42

Ok so C7090 is the bad boy in the picture. It is defective. Locate a replacement.

Then proceed to measure the voltage to ground of this input side WITHOUT the defective C7090. Once this rail returns to a normal value which should be ~adapter voltage, the output of this regulator should be the expected value.

Confirm it and update this thread.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

Just to add to this pile, if I insert only C7092, then the same scenario when C7090 was inserted happens. Does it mean that C7092 is also kaput.? What can you advise about the KOhm - Mohm fluctuations without the 3 caps?

[mon2]

Re: A1466 820-000165-A with low PP3v42

Kohms and higher is ok. The input side should not be hundreds of ohms or lower. If a cap brings down the line, skip using it.

The capacitance value of the cap is not critical but is required. The voltage rating is very important. Should be 20v or higher to be safe.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

Just a quickie. If C7090 is defective, shouldn't it show continuity when checked with a multimeter. In this case, it does not.

[mon2]

Re: A1466 820-000165-A with low PP3v42

a defective cap can also be of a low resistance but not fully shorted. If the resistance is low enough, the diode will be unable to support the load and the Vin voltage will sink. If the voltage sinks, the output will as well.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

I removed C7090 and inserted C7092. Now if i check resistance to gnd on that line, I could see resistance slowly building up in the KOhms and growing higher which leads me to believe that C7090 & C7091 are the culprits. What do you say?

[mon2]

Re: A1466 820-000165-A with low PP3v42

Yes, it is possible. Power it up to see if the Vin remains high.

[bridges_4u]

Re: A1466 820-000165-A with low PP3v42

Hi mon2,

Just to be on the same page. Would you like to power it up without C7090 & C7091.