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121 lines
3.7 KiB
121 lines
3.7 KiB
took a look at this
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may be power regulator
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or may be something downstream
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it turns off for a second, then turns off.
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hard to tell what is the problem.
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need to check all voltage rails when this is powered on.
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note that I found you can hit the power button to activate the vreg. but
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this might be dangerous to hit repeatedly.
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let's try replacing the vreg, as I want an excuse to use my hot air station
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it's possible someone just gave it too much power.
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https://www.eevblog.com/forum/repair/could-i-repair-a-beaglebone-black-that-had-was-fried-by-the-wrong-adapter/
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hehe, they say don't bother fixing. Wow...
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Steps for this:
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Attempt replacement of vreg
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if that doesn't solve it, likely something downstream.
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connect to power rails, with PSU, and watch what heats up with iso alcohol.
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I have 4 or 5 of these beagles, so I only need to find it once. In fact, maybe
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I should just skip to the inserting the Power supply in. there are a few 0805
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caps that are relatively easy to tap into...
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The board files are allegro, and I don't run win but
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the schematic shows cap labels, so this is probably the best plan of attack.
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If I don't find anything heating up, then it would point to the power supply...
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Let's do that.
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EDIT: testing all 4 beagles
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1 works, it appears.
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1 turns on all 4 status leds, but no blinks.
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2 have a brief led light on power reg, but then off. protection circuitry.
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I found 1 of them with a blown resistor on the ethernet shield to digital ground.
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it was a 0.1 ohm resistor.
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I found 2 of the 2 with brief led lights to have a cap (3.3v rail) at 12 ohms. The others
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are 400 ohms. This was mentioned on forum. Probably someone put 12v on the input, and blew the 10v
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caps... flawed design, i think.
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I'm going to remove those caps first. off to the hot air station
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i should buy some 10uf 0805. i only have through hole and 1uf 0805 (though in a project
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bag there might be one somewhere...)
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After replacing cap, there's still 12 and 5 ohms on those respectively.
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So it wasn't the caps, but something on the rail. Looks like the 3v3 rail is the only
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rail that has the short, per the other caps, didn't give me any unusual resistance, and
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also 3v3 is the one you would expect to be shorted (main v rail).
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can't find c16, which is on rtc. I need allegro to do layout searching
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3v3 goes into
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main CPU (arctic)
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usb host tps2051
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SPI board id
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24lc32
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lan adapter (3v3b)
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HDMI (3v3b)
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and some 74 logic.
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I think the cpu is the issue. Let's disconnect R14, and see if power rail boots.
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there's two inputs. one is where r14 is, another is on USB. Hopefully I don't
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have to track down usb input. don't have layout.
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removed R52, and R14, but it's still shorted.
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I believe the USB input to CPU is causing this. There aren't many other things it could be
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EDIT: looks like the 74 logic here is max 6.5 volts or so. could also be that.
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lets try to track down the short with the 6 digit dmm
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NOTE: there are two distinct 3v3 rails a and b
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3v3B comes from TL5209
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that is enabled after 3v3A is turned on. (see notes in schematic updates)
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C20 on 3v3b looks to be 0.4K ohms, so OK.
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Must be 3v3a, which doesn't have much.
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Nice idea, to separate 3v3 rails.
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based on my tracking with the 6 ohm dmm
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i found the lowest resistance somewhere around 5.5ohms in between the cpu and the ddr
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the ddr is 3v3b, so it must be the cpu.
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let's remove hte cpu, and see if power rails start.
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removed CPU. first bga removal for me.
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And sucess. The low resistance on C16 is now 0.4K ohms. So the CPU is the weak point.
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I guess this means by design, of the bbb, I will be doing some hot air bga soldering.
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it must be gods will. (ti's will)
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I removed the second bga, but this time, I pulled some pads. Of course you can
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pull pads on a bga... May not be repairable, but lesson learned.
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