Logic board repair help needed please please

[lcdcaps1]

Re: Logic board repair help needed please please

hi
i have checked

[lcdcaps1]

Re: Logic board repair help needed please please

ooops, sorry pressed enter too quickly
no shorts on l7900
no power on pin 1 on u7900
but i have checked incoming voltages on j6990
pin 8 i get 19v but pin 1 i get 13v

please help
thanks

[eccerr0r]

Re: Logic board repair help needed please please

Not enough information...what board, pictures of board, etc., etc.?
Found a schematic?

[dellxps15]

Re: Logic board repair help needed please please

voltage on q7950

[lcdcaps1]

Re: Logic board repair help needed please please

hi
i have pasted a link to schematic in my previous message
My concern is that I am not getting 3v on pin 1 on the DC-In Connector (J6990) this is on the macbook pro connector but I have looked online at the DC IN BOARD block diagram, (google images) and I see that u7600 deals with stepping down the voltage.
http://notebookschematic.com/wp-cont.../A1212-LIO.png

If I replace this will i get the right voltage measurements on J6990.
Please advise
Thanks

[wibble]

Re: Logic board repair help needed please please

>>I checked the RAM, one by one in each slot

Try without RAM, if you can get it to turn on and it beeps, this will tell you that the problem may not be voltages, but one of the ICs.

The SMC is a BGA. It has a triangle on it which points to pad A1, there is a test point just outside the opposite corner which should indicate 3V (not 3.42V) supply voltage to SMC. I think it's pads N14 and N15, it is marked on the schematic.

Generally, if you have a green light on the charger it is a relatively good sign that the basic power circuits may be working correctly.

At this point it is difficult to diagnose without clear measurements of the S5 voltages at the standard test points, such as on the coils.

[lcdcaps1]

Re: Logic board repair help needed please please

Hi
Yes tried with them.in.both slots and.without but same.symptoms
symptoms
If the charger is plugged it.doesn't.turn on when.pressing the power button or jumping pads. Pwr on but if I try just the battery it does give reaction.to.power button being pressed or jumping the pwr on.pads. but doesn't boot or stay on. Fan moves and.haed.spins.up.then shut down
If I remove charger and.plug.it in.it.does the same.thing
I mentioned this earlier

I started doing measurements an found that
on j6990 pin 8 i get 19v but pin 1 i get 13v

According to schematic diagram I should be getting 3v on.pin 1
I tested voltage directly.on.the pins of the connector on the motherboard.
My thinking is That I need to correct this before moving forward..
Logical thinking suggests this right?

I looked on the dc in board diagram and there is a chip
u7600. Will this be faulty. Should I replace.


If it does not stay on then how can I provide certain voltages
Also which measurements do you need for q7950

What's the best way to test and to know it is working.
Please note the system doesn't stay on. Only have green light on charger and when battery plugged in changes to red. I think the colour is red

Please help
Thanks

[dellxps15]

Re: Logic board repair help needed please please

u7600 is for 1.5 volt.

voltage on q7900 ? post picture of u7900 zone with high quality.

[lcdcaps1]

Re: Logic board repair help needed please please

hi
i was talking about u7600 on the dc in board ( LIO board) this should be
5V S3/S0 SUPPLY
3.3V S3/S0 Supply

how can i check voltage on q7900 when it is not starting up

My concern is that why am I not getting a 3v but instead geting 13v on pin 1
this is on j6990 corrector that connected to the DC-IN BOARD (left IO board) to power the logic board
can some one please advise if I should replave u7600 on the dc-in board
please

thanks so much people

[wibble]

Re: Logic board repair help needed please please

Just for clarity.
S5 voltatges should be always present when charger is plugged in.
S3 and S0 voltages only present after power-on pressed (or power-on pads).
Also before diagnosis you ideally need to establish that your charger is good. It should be 85W genuine Apple power supply. You can try a different charger or try your charger in a different laptop to be sure.

[lcdcaps1]

Re: Logic board repair help needed please please

hi
the charger works have tested it
i will check the measurements and report back
but could some one clarify about the 13v problem, is this normal

thanks so much

[lcdcaps1]

Re: Logic board repair help needed please please

Hi
I have been doing some measurements and have found out that u7800 has no power coming in on any pins and nothing coming out
does this mean that i need to replace this or need to replace the diodes before. (can someone confirm which diodes these are, please)

Thanks so much

[wibble]

Re: Logic board repair help needed please please

According to the schematic, U7800 is LT3470 (the regulator for G3H power rail) are you sure? Or did you mean U7900