820-2849 PP5v_S5 low

[Jimmy Spangle]

Ok guys. My first problem to post and I hope you will be able to help with this.

This is a 2010 Macbook Pro 17" that I purchased from a someone this week. Sold as 'not charging, tried 2 different chargers' and I took the chance on the basis they probably did not know you had to use an 85w magsafe. Anyway, got it, plugged in and green light straight away which is always nice. Battery is no good, so cannot tell about charging as such yet. Have checked both current sensing circuits for DC in and battery, both check out fine.

On removing rear cover I immediately honed in on two red flags. One, the fans were spotless. Two, flux around U7201. Someone has been telling uncle Jimmy porkies!!!!! Clean fans usually means someon has been in and doing something, albeit just cleaning someone has been in here first which I hate.

So, to the problem so far. Have ppbus_G3H at 8.4v. Have pp3v42 obviously and needless to say DC in etc. PP5v_S5 at C75205 was coming up at 0.7v.

Straight to that U7201 for a closer look and although it seems to be the original (no tweeer marks) and seemed to soldered well, replaced it as a matter of course. Whilst it was removed I measured pin 1 of R7901 for EN signal and got a nice steady 3.3v as hoped. On fitting U7201 that dropped to 2.4v. Replaced U7201 again just to be sure chip wasn't bad and got exact same result.

Pin 1 of C7205 is showing 0.772v with both the new chips.

A little bit baffled by this one. Racking my brains so ANY pointers will be gratefully received.

Thanks
Jimmy

 

[2informaticos]

Post resistance to ground at PP5V_S5 and both output coils L7220/60.

 

[Jimmy Spangle]

Resistance to ground PP5V_S5 at pin 1 of C7205 is 40K Ohm
L7260 is 610 Ohms
L7220 is jumping all over the place between 7M Ohm and 20K, never settling on multimeter,. Goes down from 7M to 212K to 20k, back to 94k etc etc, My meter is not the best, but good enough VC97 - not dissimilar to Fluke 15B.

I shgould correct something. Voltage at Pin 1 of C7205 is 0.772v, not 2.4 as I said in my original post - sorry.

 

[2informaticos]

We normally expect measuring on diode mode at power rails.
Post L7260 values on diode mode; red to ground and black to ground too.

200ohm scale is useful to distinquish lower values.
200k-20M is useful to check some signals also.

BTW, no power on board for such kind of measuring...

Next, post voltages at U7201, pins 12, 22, 23.

 

[Jimmy Spangle]

Thanks for your help so far.

My multimeter is a VC97+. It is alright but not as advanced as the ones I suspect you use. I can read in diode mode, but only have two options. If I opt for sound (short to ground etc) I get JUST that, sound or nothing but no ohms . If I measure without sound it displays only in volts. Does that sound correct?. So, that in mind here we go:

And yes, I do measure resistance/diode mode with power off.

L7260 is showing 0.5v in diode mode on my (crapo) multimeter
L7220 is showing 0.4v in diode mode on my (crapo crap crap) multimeter

U7201:
Pin 12 is showing 2.7v
Pin 22 is showing 3.0mV
Pin 22 is showing 7.2v

Just been reading the online manual for my multimeter and it seems that in diode mode it measures the forward voltage of a diode. I'd probably be better off using an empty coke bottle!

 

[2informaticos]

"My multimeter is a VC97+. It is alright but not as advanced as the ones I suspect you use."
I prefer a manual range one, for less than 15$.
When I use auto-range model, I will manually select the range.
No need of Fluke, or other expensive multimeters.

"Pin 22 is showing 3.0mV
Pin 22 is showing 7.2v"
Mmmmhhhhh...

BTW, are you using original Apple charger?

 

[Jimmy Spangle]

100% original. I learned my lesson many macs back.

I initially test all macbooks using my digital power supply until I know nothing too dramatic will happen, then swicth to the original magsafe 85w for certainty.

 

[Jimmy Spangle]

Can't manually select the range on mine in diode mode. Just buzz or no buzz.

 

[Jimmy Spangle]

Oh. Duhhhh! Missed that.

pin 23 is 7.2v
Pin 22 is 3.0mv

 

[2informaticos]

"Have ppbus_G3H at 8.4v
pin 23 is 7.2v"
???

U7201 should work even with 6V, but I have no idea why you get different values in the same rail.
Check diode mode at pin 22 too.
Diode mode should be "no buzz mode".

 

[Jimmy Spangle]

Sorry for confusion. When I checked the board yesterday it was showing 8.4v on G3H. When I tested pin 23 of u7201 today it was 7.2v. I didn't check the same place on the other siwde of the board today, just what you asked for. I am sure it will be the same obviously/

In the morning I will check it properly and upload all the readings.

 

[Jimmy Spangle]

Good morning everyone

This board actually got to me during the night. See if you can follow my line of thought here.

The mac had obviously been worked on by someone before as there was flux around U7201 and perhaps I should have walked away on seeing that. But like most of us I get a huge buzz if I can fix a board, especially those ones.

PPBUS_G3H is the same (7.2v this morning) wherever I check it, which would not make any sense otherwise, so you are quite right to question the different figures that I hope I explained in my previous post. But what has got to me is the low voltage (near enough zero) on pin 22 of U7201. That connects to C7203. If that was shorted to ground, that would explain something so I removed it to check. Pin 2 of C7203 is supposed to be ground, pin 1 is not. But pin 1 solder point (with cap removed) is shorted to ground. Mmmmmm... Now I am on to something me thinks....

Pin 1 of C7203 goes to pin 1 of R7248. Pin 2 of r7248 goes to Pin 1 of r7249, which in turn pin 2 of R7249 goes to ground - a voltage divider if I am not mistaken. Problem is R7248 is shorted to ground on both pins, so is R7249. What the.......? No wonder Pin 22 of U7201 is showing next to nothing!

NOW. Looking at the schematic and I think there is one of Apple's printing errors. Can anyone confirm if it is just me, but R7248 and R7249 are both listed as zero ohm? Effectively shorting straight to ground.

I am just wondering if the previous person to attack this board replaced the originals with zero ohms because the schematic says so? Obviously the originals would have been correct. Two zero ohm resistors in sieries is not an voltage divider, but the techical term I believe is 'a wire'.

Am I losing my mind, or have I found a bit of a problem?

So, if anyone can have a look at their schematic and tell me what R7248 and R7249 should actually be or an educated guess what be good so I can replace those two, eliminate the short on C7203 and hopefully we can restore life into this old mac after all?

 

[2informaticos]

Good enough to use other MacBook schematic with TPS51980.
Some Apple schematics have been found on Internet with printing error...

Remove U7201 and check if short gone.
Be aware, do NOT power up the board without U7201!!!

 

[Jimmy Spangle]

Thanks again for your input.

I did check with U7201 removed, short gone. But struggling to confirm if that actually is a voltage divider and if so what restances should be used. Got lots of schematics, but thje only ones that also show TPS51980a show the same 2 zero ohm resistors.

With C7203, R7248 & R7249 removed but U7201 re-soldered, voltages as follows:

U7201 pin 22 is 0.770v
U7201 pin 23 is 7.45v
U7201 pin 12 is 3.76v

C7205 is 0.504v

 

[2informaticos]

Don't remove anything!
Check for shorts with all pieces in place.
And post again the values after that.

BTW, you still have a problem with PPBUS_G3H.
So remove F7040/41 and post voltage at C7040.

 

[Jimmy Spangle]

Pin 1 of C7040 is 9.7v with f7040 an f7041 removed

 

[Jimmy Spangle]

Put F7040 and F7041 back on. getting 8.4v at L7031 pin 2 and the same at pin 23 of U7201

the one part I am confused over is the two resistors R7248 and r7249. can anyone confirm what they should be please?

 

[2informaticos]

Be aware of "NO STUFF" marking in schematic.
In your case, means R7248 is not soldered; only R7249 is in place.
If you put both, will short VREG3 to ground...

8.4V is correct for PPBUS_G3H if machine has 2 cells battery.
Replace U7201 with new and pay atention to solder perfectly all its pins.

 

[Jimmy Spangle]

Aha. Now that makes sense. I missed that!

The previous guy obviously put both resistors on and that is what threw me off. Never asume anything they say - for good reason.

I am guessing that the U7201's I have fitted will have blown then? My soldering is as good as any I have seen, so quite confident about that part. My last two TPS51980's. I'll order another one now and we'll see what comes of it in a couple of days. I will update then.

Voltage at pin 11 supposed to be zero? Obviously fitting a zero ohm R7249 obviously shorts that to ground in effect.

 

[2informaticos]

That will not kill U7201.
VREG3 should get protected.
Put the last soldered U7201 there.
If no short, try it.

Be aware, if DRVH1/2 are not properly soldered, Q7220/60 will blow.
Is better to check continuity...