Hardware 3v3 circuit short to ground

Ttm3 · Jun 3, 2020

This unit had a bad USB port. Changed that out and I had a short on pin 6 of m92t36. Remove m92 short is still there. Remove p13usb short is still there. Remove bga ic above audio chip short is still there. I removed all of the caps i could find on that circuit short is still there.

What else could be pulling this thing down?

FAST6191 · Jun 3, 2020

Any chance of some photos of the PCB in question?

I would also be looking for any crushed layers.

bombob · Jun 3, 2020

Check usb pins continuity.

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Ttm3 · Jun 3, 2020

FAST6191 said:
Any chance of some photos of the PCB in question?

I would also be looking for any crushed layers.

Ttm3 · Jun 4, 2020

FAST6191 said:
Any chance of some photos of the PCB in question?

I would also be looking for any crushed layers.

Just retested everything and there is resistance of about 6-7 ohms to gnd on the 3v3 line. Any idea what else is driven by that circuit?

Pintglass · Jun 4, 2020

Ttm3 said:
Just retested everything and there is resistance of about 6-7 ohms to gnd on the 3v3 line. Any idea what else is driven by that circuit?

Cpu

Ttm3 · Jun 4, 2020

Pintglass said:
Cpu

That's what I'm afraid of

Pintglass · Jun 4, 2020

Check the usb data lines D+ and D- to see what resistance to ground you get on them.

Ttm3 · Jun 4, 2020

Pintglass said:
Check the usb data lines D+ and D- to see what resistance to ground you get on them.

5.19 ohms to ground & 4.89 ohms to ground
.31 to each other

Pintglass · Jun 4, 2020

I can’t remember what values they should be exactly but there normally a lot higher than that

Check the esd protection device if it has one depending on version, if this is ok or not installed I’d say If your readings are correct your issue is cpu damage

Ttm3 · Jun 4, 2020

Pintglass said:
I can’t remember what values they should be exactly but there normally a lot higher than that

Check the esd protection device if it has one depending on version, if this is ok or not installed I’d say If your readings are correct your issue is cpu damage

Are you talking about the smd device on side a next to the USB port?

Pintglass · Jun 4, 2020

The esd device is a 6 pin ic just above the 2 test points next to the fuse

Ttm3 · Jun 4, 2020

Pintglass said:
The esd device is a 6 pin ic just above the 2 test points next to the fuse

I removed it and it made no difference

Pintglass · Jun 4, 2020

Then it only leave's the SOC

Ttm3 · Jun 4, 2020

Pintglass said:
Then it only leave's the SOC

I'll pull that off and see what I got

laotoulyh · Jul 31, 2020

I repaired one yesterday, and it had the same fault, it was PI3USB

Pintglass · Jul 31, 2020

laotoulyh said:
I repaired one yesterday, and it had the same fault, it was PI3USB

Not the same fault op said he removed PI3USB and fault remained

SheriffBuck · Aug 2, 2020

Ttm3 said:
I'll pull that off and see what I got

I've been tracing the 3.3v rail and it feeds a lot more than just the P13 and the M92. How can you be so sure that it's the SOC @Pintglass ?

@Ttm3 how did you get on pulling the SOC?

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Ttm3 · Aug 2, 2020

I didn't pull the soc on this unit. I pulled it on another but had no luck reballing... I'm currently working on about 20 boards and I think I threw this one in a "get to it later" box

Hardware 3v3 circuit short to ground

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