Author Topic: 1708 No USB power after U1 replacement  (Read 1535 times)

Offline Andrunin

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1708 No USB power after U1 replacement
« on: December 04, 2020, 04:11:36 AM »
Here is another puzzle.


I replaced the USB Port because it made a bad connection and checked continuity between the plug of a cable and the components on the port. All seems ok with the USB port.


U1, D23 and the trace near U1p3 were all scorched. I replaced U1, D23 and ran a jumper from p3 to L2. The board works ok with batteries, but has no power with USB.

I can measure 5V at C7, but nothing at pin3. On a good board I get 3V there. I did this repair on 3 boards with the same problem, but it worked only on one board. What could it be? Is it a bad U1 chip?












These are from a job lot for repairs, but turned out it was a box of junk where the seller assembles the devices with components that he couldn't repair.. I managed to fix most of them so far but they were incredibly hard to fix. Good thing is I learned so much from trying to fix these
« Last Edit: December 04, 2020, 04:12:43 AM by Andrunin »

Offline RDC

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Re: 1708 No USB power after U1 replacement
« Reply #1 on: December 04, 2020, 12:14:15 PM »
7 of those 8 pins on that chip make connection to the PCB, so you need to make sure they all are and that no pad/trace was torched and broke making an open there.

Also need to check the Resistors there (R16, R17, R18) to make sure they haven't gone open or out of spec.

1 - NC, but measures ~4.5v
2 - USB 5v
3 - 3v
4 - GND
5 - 3v
6 - GND
7 - 0.6v
8 - ~4.5v
Screwing up is one of the best learning tools, so long as the only thing you're not learning is how to screw up.

Offline Andrunin

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Re: 1708 No USB power after U1 replacement
« Reply #2 on: December 05, 2020, 03:48:29 AM »
Ah yes thanks a lot. I had a cold solder joint at pin 8 in both cases and now they work. I'm still quite new to this stuff and not sure what my mistake was. I used hot air and a lot of flux for these components.

Just one more question. In one case I didn't have the exact same model for the diode D23 because I ran out of them from donor boards. I used one with a A2 R2 marking instead of 2D. It has a higher voltage drop of 0.6V instead of 0.2V. It works fine anyway from what I can tell. Do you think that's going to be lasting repair or should I get the correct one?
« Last Edit: December 05, 2020, 04:32:45 AM by Andrunin »

Offline wickated

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Re: 1708 No USB power after U1 replacement
« Reply #3 on: December 05, 2020, 05:36:24 AM »
low drop diode - shottki

Offline RDC

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Re: 1708 No USB power after U1 replacement
« Reply #4 on: December 05, 2020, 06:02:36 AM »
It'll be fine in that case as it's not in any type of switching circuit. There's no reason at all for it to be a Schottky as the USB 5v - 0.6 = 4.4v to the input of U1, well above the 3v output it generates. It'll be a shade less efficient, but that's all.
Screwing up is one of the best learning tools, so long as the only thing you're not learning is how to screw up.

Offline wickated

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Re: 1708 No USB power after U1 replacement
« Reply #5 on: December 05, 2020, 06:20:18 AM »
It'll be fine in that case as it's not in any type of switching circuit. There's no reason at all for it to be a Schottky as the USB 5v - 0.6 = 4.4v to the input of U1, well above the 3v output it generates. It'll be a shade less efficient, but that's all.
and also most of diodes on xbox controllers are reversed - from ground to line, which mean they are for protection

 

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