How to check sony protection circuits

SONY VGN-NS11S MBX-195 M790 Rev 1.1 1P-0087J04-8011 PCG-7141M ,

Sony’s protection circuits are hard to troubleshoot. It involved too many components. About mbx-165 protection circuits:

1. Power passes PF1 becomes DC_IN, at this point, Max1909 start to work. ACIN, DCIN high, LDO 5V, REF 2V(must have, can’t remember exactly voltage). Max1909_PDS low to drive PQ25 (don’t know exactly voltage, but lower than DC_IN).

2. PQ25 converts DC_IN to DC_IN_MOS. Here comes the hardest troubleshooting of the sony protection circuit.

PQ26’s gate must be low and it was a signal called DC_IN_G1. So where is this DC_IN_G1 from? In a normal situation, it max1909_pds through a resistor. Now, you have 19V of this abnormal signal.

we check it by few steps:

1. check pc3, is it short?

2. ac_off_3# is high? if it is high, check PQ31, PQ20, PR116, PR119, and PR120.

3. ac_off_3# is low? check the ac_off_3# signal, many components involved: DC_IN part from PD2 to AC_OFF_3#. From the input of PU13 (2nd pin, max1909_LDO) to PQ24A, PQ59, PQ24B.

I hate sony’s protection circuit, too many troubles. The last time I fix one such problem on sony mobo is PD2 leaking, spend almost 5-6 hours. And the solution to it? Just remove the PD2, which means it does not matter if it is PD2 or not the mobo still working. Extra protection means extra troubles and faults.

Q. USB power problem

A. The following solution only applies that USB no power, if the USB device gets power but can’t be detected or can’t be recognized by the system, that indicates a southbridge problem.

To get power for a USB is very simple. use a multimeter to find out which USB pin is ground, the pin on the other side will be the power. for example, say pin 4 is ground so pin 1 will be the power.

connect power pin to 5v you can find on the motherboard, usually a big inductor(be careful, when you measure the voltage, put the battery in as well, some mobo the inductor for charging circuits give you 5v if you don’t put the battery in but jump to battery voltage once you put in the battery, such high voltage will burn your USB devices). connect it on the different side of the inductor that MOSFET connects to(or should I say power outside?) so you can get a smooth waveform, don’t connect to the same side of MOSFET(this is power inside).

Q. My Lenovo SL400 screen went dark (the image there, is just very hard to see, a torch will show it is there though).

A. When we fix such a problem, usually we do the following:

1. Find a known good lamp or screen, plug it into an inverter see if it lights up. if it lights up so you need to change your screen’s lamp.

2. If it did not light up, do the following:

a. Check power(either 5V or 19V), enable signal(3V), and brightness control(3V) are presented. (all testing be done with adapter plug-in).

b. If all those are presented, then change the inverter otherwise
c. need to find out which wire is power, which is enabled, and which is brightness. people find it hard in here because they don’t know how to find out which is which.

Power always connects to fuse (also need to check fuse is ok). for the other two, you need to check inverter PWM’s datasheet to make a decision. Just start from PWM’s EN and Brightness pin, and trace back to the connector. After you find out, make sure all these wires have normal resistance to the ground, otherwise, you have to cut off the abnormal wire. Then try to find the exact voltage from the mobo and connect to the inverter, by doing this you do not fix the problem but bypass it. It is easy to work around it rather than fix the problem.

1. Is there a popular model of power supply that you can recommend?

2. Do you use mini-grabbers to attach the power supply to a laptop or do you have a collection of common dc plugs?

3. How do you use Dell laptops that have a third wire to identify the power supply?

I just burn one power supply today, this is 4th one I have burnt in the last 3 years. Lucky it was not connected to any laptop when it was burnt. Its output voltage jumped from 19V to 50V, at this voltage all laptop’s power circuits will burn through, I have 3 laptops burnt before.

There is no popular model as I know, but at least 5A/30V. Get an industrial grade if possible, because a non-industrial grade power supply can’t even run a laptop for more than one hour, or you face the risk to burn your power supply? in turn, it will burn the laptop. It is sufficient for repairing jobs but not enough for machine testing. It must have an MA reading because sometimes the reading is less than 0.01A.

I have a collection of DC plugs, made from faulty chargers.

Ignore the 3rd pin of the dell charger, it is only for PS_ID, only use for charging the battery. Without this PS_ID machine still, run but just can’t charge. But some old dell like 5150 will not work our power supply, lucky we don’t have any such machines to fix.

1. Is there a “generic” current profile for laptops or does each laptop have its unique current profile?

2. In your example for DV9000, you say “0.01? 0.3 -0.9? 1.1? 0.9? 1.2 -1.45 then display” Can you explain what happens at each current change state?

3. Do you need a power supply that logs the current or does it change slow enough to visually monitor the different current states?

4. If a laptop gets power but no video, how do you isolate the failure between northbridge, southbridge, SIO, and bios?

1. Every laptop has its unique current profile. But although the reading is different, the up and down (jumping) are similar.

2. The dv9000’s current reading may not be very accurate, I suggest you first move the ram away and see how the current changing, then put back the ram and check it again.

3. not very fast, your eyes can catch the changes.

4. this is a big question, may need a full textbook to explain it. The simple answer for this question: a. current reading, b. LPC wave, c.SMB wave. we have explained the current reading before. LPC waves are measured on EC, if you can’t find an LPC wave, that means no communication between EC and SB, PLTRST presents or not it is not then SB problem, etc. SMB waves are measured on ram slot, communication between ram and northbridge, H_RESET present or not, if it is not then NB. There are also so many signals that need to check, can’t remember what is now.

I think the hardest fault for beginners is why the laptop does not power up, not the faults after it powers up.

Let’s see the example of how we troubleshoot a non-powering machine,

Model: Acer 5737

EC: kbc926

symptom: can’t power up

checked: 3ALW, 5ALW presented

1. check whether the power button has power or not, press it to see if pulls down the voltage.

2. check kbc926’s 32 pin, which is on/off see the signal received.

3. EC_VCCA is high?

4. check if EC_RSMRST is high?

5. LID_SW# is high?

6. ACIN is high?

7. EC_CRY is correct? (32.76Khz)

8. Southbridge crystal correct( which is X4, also 32.76KHz)

9. PBTN_OUT pull low when you press the power button?

if all above have no problem, consider the south bridge fault. for this machine, there is a single bridge? southbridge/northbridge/VGA combined. North bridge’s functions are mostly taken over by the CPU.

This laptop will run on ac charger it wilL NOT run on a fully charged battery.

This is what we called protection circuit fault.

Looks like discharging has a problem. When discharging MOSFET has a problem, or the Gate voltage is not correct, the 18V of main power will directly go to the battery.

The current will be very large when you have short discharging MOSFET if you plug the charger in and have the battery installed at the same time. A laptop will detect this abnormal current and refuse to start up. Remove either one, the machine can start up.


Please Note:

The first step to troubleshooting is to monitor the current change. usually, current reading can tell what was wrong and is quite accurate.

CPU faulty rarely happens. I only see no more than 5 to 8 CPU faulty during 10 years.

CPU kills motherboard happens on me once, and that motherboard in turn to kill another good CPU, and this is p3 CPU.

Don’t worry about the CPU, 99% chance it is good.

Try to do this, find a current meter, cut off the wire of the power adaptor, and connect the current meter to the wire. The meter must be able to read at least 0.01A

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