820-3536 Reported slow performance, fails sensor group test, liquid exposure

[Jay]

I ran ASD when the Mac came in and it passed all but 1 test:
Sensor Group (test#5)
Sensor Failure=[Voltage (VD0R) -- DC-In] Failed Value=20.045898
ERROR -- 2 [Sensor reading above alarm point] -- TEST FAILED

Opened it up and found what looks to be small dried up blobs of soda that were easily removed with no signs of corrosion on the following:
- J6100 pins 31, 1, 3 and 5.
- C1804 pin 1
- C7090
- Next to U7090
- On and around U3090
- Possibly under U4000 by pin 73
- R9704

Cleaned all of the above and gave U4000 a bath, then put it back together just to see if there was any improvement in ASD.
ASD fails the same test. DC in board is clean as is the connector on the board.
Booted into user environment and the Mac is snappy and I can not find anything that runs slower than it should.

Would still like to resolve that error though. Any idea of where to start looking?

 

[Jay]

Checking Q5490 and related circuit next (having a searchable PDF certainly helps to find "VD0R")

 

[smiba]

VD0R is simply too high because you're using a charger for a 15" macbook, this can be ignored and should not cause the SMC to run the CPU at a low clock speed. It will probably go away when you unplug the charger

 

[Jay]

Alright so I checked out the circuit around Q5490, measurements are:
Q4590
- pin 2 - 3.35V
- pin 3 - 20.74V
- pin 4 - 20.78V
- pin 5 - 10.3V
- pin 6 - 0.0V
I believe that means no enable signal (assumption) so checked the following:
- PPDCIN_G3H_ISOL - 20.75V
- R5492, R5491, R5498 and R5499 all have the right resistance
- R7020 pin 2 - 20.5V
- U7100 pin 2 - 20.5V
- C7105 pin 1 - 5V
- R7105 pin 2 - 20.5V

The 20+ V measurements throw me off a little because the schematic says those should be 18.5V. I typically see lower than what the schematic says, not higher. Is this ok?

Where should I look next?

 

[Jay]

smiba , your comment didn't show until I posted my latest comment and the page refreshed. I'll run ASD from the battery to confirm, good to know Would that also cause the measurements of 20+V where I should be seeing 18.5V?

 

[smiba]

20V or even 20.7V is definitely higher then I would expect from a 85W magsafe 1 charger (are you using an genuine charger from apple?), but the ISL should be able to handle input up to 25V and all the capacitors and components on the circuit are rated for 25V or better.
I don't think it will put the system under too much stress but if you have any other chargers try and see if they have a more acceptable voltage

What is the system clock rate running at under load? Temprature in check? CPU_PROCHOT_L high?

 

[Jay]

Thanks, will try another charger tonight. Temperature wise everything is good, fan doesnt start blasting and it's fast and responsive under normal load. The charger as far as I know is a genuine Apple brick.

 

[Jay]

"What is the system clock rate running at under load?" How do I test this?

 

[smiba]

Just use something like Intel Power Gadget or one of the other tools available for OS X.

But whats wrong with the machine? Because other then the one error from ASD by using a 85W/15" charger it sounds like the system is working fine isn't it?

 

[Jay]

Right now I can’t find a thing wrong. It was handed to me with “it runs slow”. Should have done a test to verify before cleaning the board.

 

[dukefawks]

It will not run slow if voltage is above the high point. As long as ASD is not reporting sensor issues and it has a working battery it will probably run fine.

 

[Jay]

Alright, will mark this one as done then. Just for education sake, what would cause this thing to run slow? If you look at the first post, could the small liquid blobs I found be a cause? Pins being bridged here and there, specially the JTAG but no corrosion. Would just like to know if I possibly fixed it by cleaning the board or if I should subject this to more testing.

EDIT: Basically I don't get the concept of a short causing slowness. A short causes it to not work at all in my limited experience so far.

 

[Jay]

Small wrinkle. I ran ASD from the battery and it fails the same sensor tests but shows an additional error. Connected charger (my personal 85W) and got the original errors back (which I will ignore based on feedback earlier), did not expect an error when running from battery power though.

 

[smiba]

Hm apparently they have a low limit for DC-In, I thought they hadn't (in the older models I'm almost confident they hadn't) but maybe my mind is wrong.

Anyways they can still be ignored as they're just related to DC-In, no worries

 

[dukefawks]

What does it say explicitly at the start of the test?

 

[Jay]

I know Duke
Thanks for the help guys, thing runs fine. Case closed.