MBX-225 BQ24753A issue

[rookieme]

I have a MBX-225 with problem at DCIN.
I have attached MBX-224 schematic as this is and identical one.
At first I had 19V coming to PR4 but the second I pushed power on it got 0V as before pressing ACDRV# was 12V and after that 19V.
I did replaced BQ24753A with a NEW one and now I get 19V at ACDRV# and 0V at PR4 [this is Permanent]
ACDET = 2,4V, ACGOOD# = 0V, OVPSET = 1,21V.
Resistance at PR4 is 19kohm so no shorted cap at output.
What am I missing?

[meritosari]

Re: MBX-225 BQ24753A issue

Check AC_OFF_3# signal at Page 82 System SCP Protect
I think that AC_OFF_3# should be 19V, so PQ35A enter to OFF state and DC_IN_MOS not generated to be ACDRV#. At same time DC_IN_MOS not cross in PQ35B to generated DC_IN G1.

Check component around that section.

Also I've noticed OVPSET be lower than ACDET, from calculating resistor divider PR18 and PR20, should be the volt same as ACDET.
CMIIW

[rookieme]

Re: MBX-225 BQ24753A issue

Thank you for your reply,
The area at system SCP protect looks fine, also I did a slight reflow just in case as it has happened before PR6 to overheat due to bad solder.
AC_OFF_3# is 13V [PR139 pin2 13V, pin1 17V].
PQ35A pin5 17V, pin3 18,2V, pin4 18,4V
PQ35B pin2 14V, pin1 18,4V, pin6 18,4V
Also you're right that ACDER should have the same voltage with OVPSET as they have same values at their voltage dividers - if I remove they both have 2,4V.
That's stange as it happens with both new BQ24735A that I have tryied.
With the old one both voltages are 2,4V, ACDRV# is 12,5V and
PQ35A pin5 17,7V, pin3 12,4, pin4 18,9V
PQ35B pin2 17,5V, pin1 18,9V, pin6 12,4V
Do new BQ24735A need backing chamber first as BGA chips? I haven't faced same problem before.
Now with the old BQ24753A if it stays powered on I get no power to all coils so I'll look the rest of the system

[rookieme]

Re: MBX-225 BQ24753A issue

at the moment I have a theory that new BQ24753A are bad and the old ok, also a possible issue somewhere else at the system as now it powers on and soon after protection circuit kicks in and cuts the power, so something could draw too much current?

[dellxps15]

Re: MBX-225 BQ24753A issue

repaired a bad 225 mainboard this month. problem was black screen, and after a bit short on 19 volt rail. it was pq43 that was bad and also bad gpu.

if mainboard got a short u wont get any good voltages on the board as it has system voltage protection.

[meritosari]

Re: MBX-225 BQ24753A issue

Probably dellxps15 was right. There is something not good in High Side mosfets on one of those every PWM regulator.

I would try inject with low voltage at DCBATOUT to make sure these rail was OK. a little trick when injecting on DCBATOUT, measure on every big coils if you get voltages. if so then High side mosfet have shorted. This not good because the voltage can goes trough to output PWM. Meanwhile always monitoring current ampere drawn on your PSU.
Otherwise, you could inject with 12V. Just totally be carefull
In my experience, Have found that IC LDO for supply to EC was bad (PU9).
I think that signal AC_OFF_3# used for protecting main circuit from 3 point, RTC circuit, LDO/SMPS 3V 5V and DCBATOUT.

Have you try it with battery?

I've learn the SCP protection from Jialinc's post on whirpool forum (page 41). Sony SCP protection it's very interesting for learn.
Extra protection means extra troubles and faults, him said. See attachment

A little Hijack your threads.

On my bench there is mobo Quanta HK8 wasn't solve too (more than 2 month). Similar problem, 19V didn't cross at first mosfet. DCBATOUT work with batterry, but still can't power on. indicator of Charging didn't lit too. Don't know how to figure out the main issue.

There is one thing what I've noticed that if cmos doesn't present Voltages on main battery won't came out. 3V_RTC need to activating -SYS PRS signal. Mean activated the main battery.

[rookieme]

Re: MBX-225 BQ24753A issue

The battery is dead and not charging.
I'm not sure that this could be an issue at one of the high side mosfets as sometimes works ok and other times powers on for a second before cutting the power.
It's interesting technique to inject power at DCBATOUT, but will it make the buck converters to work? I think that the kbc won't turn them on as it monitors the ACIN_EC comming from the BQ24753.
For a start I did a good reflow at every buck converter and it's mosfets and for now it's working. I did it as I thought that it could be a bad soldering that could cause it sometimes to work and others not.
I'll reassemble it and keep you informed.

[meritosari]

Re: MBX-225 BQ24753A issue

The battery is dead and not charging.
I'm not sure that this could be an issue at one of the high side mosfets as sometimes works ok and other times powers on for a second before cutting the power.
It's interesting technique to inject power at DCBATOUT, but will it make the buck converters to work? I think that the kbc won't turn them on as it monitors the ACIN_EC comming from the BQ24753.
For a start I did a good reflow at every buck converter and it's mosfets and for now it's working. I did it as I thought that it could be a bad soldering that could cause it sometimes to work and others not.
I'll reassemble it and keep you informed.

So now it more make sense, solder joints often can cause intermittent like that.

[rookieme]

Re: MBX-225 BQ24753A issue

Second day and still works.
I'm gonna test is a couple of days more and return it to its owner.
Thank you all for your time.

[ahkh_72]

Re: MBX-225 BQ24753A issue

HI
I faced to the same problem as you .
And i solved it by cleaning pq33 area and resolder it.
Thanks.

[Ruan]

Thank you.