820-00923 USB meter cycles every 4 seconds on all ports

[No-Clean]

Clean board, I have already checked all rails on page 120 and 121 for shorts and all rails are fine, I have also measured in diode mode all LDO lines on all 4 CD3215s and they are all fine too.

When inspecting with thermal camera U7800 flashes a little hot when voltage comes in, but no shorts are detected around it or anywhere else on this board.

 

[2informaticos]

Looks like board try to start and goes off because some protection is triggered.
Did you try SMC bypass?

PPBUS_G3H pulses at least?

 

[No-Clean]

PPBUS_G3H starts at ~5V for about 2-3 seconds then goes up to ~18V for about 1 second then it restarts and repeats.

SMC byspass makes no difference.

 

[2informaticos]

Are you sure about 18V at PPBUS_G3H???
Do not confuse between PPBUS and VBUS input...

 

[No-Clean]

Ok just measured again and multimeter for the first 2-3 seconds is always around 4.5-5V then shows OL for about 1/2 second then shows anywhere from 4V all the way up to 18V for about 1/2 second and repeats.

And yes that would be PPBUS_G3H measured at C6483

USB meter never shows any numbers, just blank screen.

 

[No-Clean]

I just realized my USB meter is dead, but with new meter is the same thing, but now I can see that when voltage tries to go from 5V to higher that is when it restarts.

 

[2informaticos]

Check Q7030/40 for short.

 

[No-Clean]

You are a mastermind!

I replaced both and that was it, however no short was found, I replaced them because upon inspection with thermal camera those 2 IC chips were flashing hot briefly.

 

[2informaticos]

I was talking about short between some of their pins, NOT connected to ground!

 

[No-Clean]

Well either way its now fixed, I just noted this for next time

 

[2informaticos]

Good job and thanks for feedback.
I do not remember another post about this fail, really rare.