# External power supply damaged board?

**URL:** <https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207>\
**Category:** LimeSDR\
**Created:** [9 May 2017 00:07 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207 "2017-05-09T00:07:08Z")\
**Posts on this page:** 20\
**Page:** 2

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**Author:** ![jslatten](https://avatars.discourse-cdn.com/v4/letter/j/f4b2a3/32.png) [@jslatten](https://discourse.myriadrf.org/u/jslatten)\
**Post date:** [14 May 2017 19:07 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/21 "2017-05-14T19:07:04Z")

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Yes, it does look like fr38 is burned. What is its function and how can I jump across?

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**Author:** ![KBBF5](https://avatars.discourse-cdn.com/v4/letter/k/edb3f5/32.png) [@KBBF5](https://discourse.myriadrf.org/u/KBBF5)\
**Post date:** [14 May 2017 20:07 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/22 "2017-05-14T20:07:27Z")

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It appears its function is a fuse or choke. I would not jumper it as it blew for a reason and is probably a secondary effect from another issue. Can you check with a multi-meter the resistance between ground and FX3\_VBUS on C273. Also further pictures requested above would be great!

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**Author:** ![Zack](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/zack/32/89_2.png) [@Zack](https://discourse.myriadrf.org/u/Zack)\
**Post date:** [15 May 2017 06:51 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/23 "2017-05-15T06:51:33Z")

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Hello @jslatten,

FR38 is a one component of the VBUS voltage filter which is used to detect USB voltage by FX3 MCU. It is possible to burn FR38 if voltage from USB is higher than 6V. As a consequence FX3 MCU may be burned out as well.  
Could you measure voltage between GND and VCC\_EXT and between GND and VCC\_INT on J21 pinheader as shown in picture bellow.

 ![](https://canada1.discourse-cdn.com/flex034/uploads/myriadrf/original/1X/801cc9272ec89b673352f3e38731d2e4be24d696.png)

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**Author:** ![BelmY](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/belmy/32/843_2.png) [@BelmY](https://discourse.myriadrf.org/u/BelmY)\
**Post date:** [18 May 2017 04:45 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/24 "2017-05-18T04:45:32Z")

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Hi everybody,  
just to know, is there any relation with the symptoms and problems described in this post?

> [@No lights when powered from EXT power supply](https://discourse.myriadrf.org/t/no-lights-when-powered-from-ext-power-supply/987):
>
> Hi All, Been using my Lime board for a few days - mostly powered by the USB3. RF signals through either of the 3 RF paths are quite weak. I looked at the Quick Test procedures: [https://wiki.myriadrf.org/LimeSDR-USB\_Quick\_Test](https://wiki.myriadrf.org/LimeSDR-USB_Quick_Test) Loopback test with WCDMA has the right profile, but also a few spurs (i have LimeSDR in luftek’s enclosure+ front/rear plates). Having read in a few threads that USB power is not the cleanest one, i switched to 6V EXT power supply. With EXT power supply i do not get an…

Also, if a live connection (while is USB powered) to EXT Supply plug was done, is it possible an spike (if different grounding system is used, current flows balancing), apart from the absolute maximum voltage exceeding, could damage the board (i.e. the more sensitive components in the path)?

Any recommendation to prevent this potential damage risk (i.e. as power up sequencing, power source limitations, no live connection, safe USB removal, etc)?

Cheers  
BelmY

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**Author:** ![hTo137](https://avatars.discourse-cdn.com/v4/letter/h/ba8739/32.png) [@hTo137](https://discourse.myriadrf.org/u/hTo137)\
**Post date:** [28 May 2017 19:34 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/25 "2017-05-28T19:34:30Z")

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[quote=“BelmY, post:24, topic:1207, full:true”]Any recommendation to prevent this potential damage risk (i.e. as power up sequencing, power source limitations, no live connection, safe USB removal, etc)?  
[/quote]

My feeble recommendation is to not use just any wall wart power supply. And definitely use a PS that’s in the specified range recommended.

I’m not sure what you mean by “safe USB removal”? Please explain.

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**Author:** ![BelmY](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/belmy/32/843_2.png) [@BelmY](https://discourse.myriadrf.org/u/BelmY)\
**Post date:** [29 May 2017 23:01 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/26 "2017-05-29T23:01:05Z")

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Hi hTo137, thanks for the recommendations.

I’ll try to explain myself about this concern

> [@hTo137](#):
>
> I’m not sure what you mean by “safe USB removal”? Please explain.

Currently, using the Myriad USB driver there is no way to safely remove LimeSDR (with the Zadig ones is possible), so, assuming the current value is not too low when is powered only through this USB3 port, there is a certain risk to damage the circuitry when unplugged. In the same way, when the power supply is taken from the EXT supply, even if the current level is lower in the USB3 (or USB2) port, there are shared power supply lines which could be also affected when the USB is unplugged or when the EXT power supply is plugged/unplugged.

Regards  
BelmY

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**Author:** ![hTo137](https://avatars.discourse-cdn.com/v4/letter/h/ba8739/32.png) [@hTo137](https://discourse.myriadrf.org/u/hTo137)\
**Post date:** [30 May 2017 16:38 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/27 "2017-05-30T16:38:40Z")

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> [@BelmY](#):
>
> Currently, using the Myriad USB driver there is no way to safely remove LimeSDR (with the Zadig ones is possible), so, assuming the current value is not too low when is powered only through this USB3 port, there is a certain risk to damage the circuitry when unplugged.

Please provide more info. You are saying that the Linux USB(2,3) driver (i.e. the kernel) is not allowing a device to be safely unplugged? Or are you saying the Cypress-FX3 driver/firmware is lacking something needed to allow safe removal of the device?

[quote]  
In the same way, when the power supply is taken from the EXT supply, even if the current level is lower in the USB3 (or USB2) port, there are shared power supply lines which could be also affected when the USB is unplugged or when the EXT power supply is plugged/unplugged.[/quote]

A similar but separate problem that you’re talking about? Is the deficiency you’re claiming a driver/firmware one or a hardware one?

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**Author:** ![BelmY](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/belmy/32/843_2.png) [@BelmY](https://discourse.myriadrf.org/u/BelmY)\
**Post date:** [1 June 2017 07:06 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/28 "2017-06-01T07:06:13Z")

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> [@hTo137](#):
>
> Please provide more info. You are saying that the Linux USB(2,3) driver (i.e. the kernel) is not allowing a device to be safely unplugged? Or are you saying the Cypress-FX3 driver/firmware is lacking something needed to allow safe removal of the device?

Yes, at least in Windows 10, if the Myriad USB driver is used is not possible to safely unplug the LimeSDR. I don’t know how this can be corrected (for instance with the Zadig WinUSB drivers is possible to safely unplug it).

> [@hTo137](#):
>
> A similar but separate problem that you’re talking about? Is the deficiency you’re claiming a driver/firmware one or a hardware one?

It must be noted, it is my assumption, if the LimeSDR can be not unplugged safely, then as the power lines are shared (there is a switch, but is not clear how it performs), any connection (USB or EXT) without following certain steps could affect negatively (i.e. current spikes, voltage variations, …).

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**Author:** ![EGX](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@EGX](https://discourse.myriadrf.org/u/EGX)\
**Post date:** [1 June 2017 14:58 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/29 "2017-06-01T14:58:28Z")

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This is indeed an interesting topic, and also happen to be the first one I read. So I just received my LimeSDR, and since there is no information at all in the package about how to connect it, I’m actually scared of connecting it! 😕

Looking at your website including many links to/from/on GitHub, I don’t find any info anywhere about how to actually connect the thing. This is especially so given that the USB3 cable has 2 connectors to one.

I want to know:

1. How to connect the 2 USB cables? (E.g. Does both need to be USB3?)
2. How to connect external power (and if it is needed)?
3. What is the optimal power supply rating needed?
4. Can I connect the SDR even if there are no antennas connected? (Would hate to ruin the RFFE just because of missing load…)

Can someone please point me in the right direction?

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**Author:** ![hTo137](https://avatars.discourse-cdn.com/v4/letter/h/ba8739/32.png) [@hTo137](https://discourse.myriadrf.org/u/hTo137)\
**Post date:** [2 June 2017 21:41 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/30 "2017-06-02T21:41:59Z")

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> [@BelmY](#):
>
> Yes, at least in Windows 10, if the Myriad USB driver is used is not possible to safely unplug the LimeSDR. I don’t know how this can be corrected (for instance with the Zadig WinUSB drivers is possible to safely unplug it).[/quote]  
> Do you have some evidence of this? You experienced a failure? What kind of failure?  
> You don’t give any data.
> 
> [quote]It must be noted, it is my assumption, if the LimeSDR can be not unplugged safely, then as the power lines are shared (there is a switch, but is not clear how it performs), any

So it’s only your assumption but that’s all? Also you keep saying “safely”. Please define what you mean.

> [@](#):
>
> connection (USB or EXT) without following certain steps could affect negatively (i.e. current spikes, voltage variations, …).

What certain steps? Why so hesitant to explain things in exact terms? In USA we call this “beating around the bush”. 🙂

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**Author:** ![BelmY](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/belmy/32/843_2.png) [@BelmY](https://discourse.myriadrf.org/u/BelmY)\
**Post date:** [3 June 2017 10:14 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/31 "2017-06-03T10:14:09Z")

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> [@hTo137](#):
>
> In USA we call this “beating around the bush”. 🙂

In Spain we say _“A buen entendendor con pocas palabras basta”_ (english translation could be: _“A word (few words) to the wise is (are) sufficient”_😉

Anyway, I’ve tried to explain myself a little bit better than before through this compilation:

[LimeSDR\_Explanations](http://frandroid.tecnoforum21.com/archivos/LimeSDR_Explanations_about_USB_and_EXT_power_supply_03ok.pdf)

As main conclusion, if I’m not wrong, the v1.2s board has not implemented the automatic power source selection (status) functionality and in the v1.4 (r4 or r7) one is not sufficiently clear how it performs, so, again, certain steps/recommendations to plug/unplug the power supply should be given by LMS or somebody able to understand/explain the whole functionality.

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**Author:** ![JayKominek](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/jaykominek/32/955_2.png) [@JayKominek](https://discourse.myriadrf.org/u/JayKominek)\
**Post date:** [3 June 2017 16:36 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/32 "2017-06-03T16:36:17Z")

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The data sheet for the FPF3042 indicates that V\_IN\_SEL is bidirectional. When EN is low, then Vin\_sel becomes an output, which can obviously be ignored. The relevant truth table appears on page 5 of the data sheet. On both v1.2 and v1.4, EN and DF\_IN are tied to ground, so the chip will prefer V\_IN if both power lines are above V\_UVLO. Otherwise it will take whichever one is above V\_UVLO. The choice will be indicated on V\_IN\_SEL.

It looks like FPF3042 is bidirectional between its Vout and Vin / Vbus pins(!), depending on which input is selected. (3 paragraph of datasheet description section.) So I could imagine a chain of events like:

1. Attach USB & External power, in either order. Probably everything is fine.
2. FPF3042 allows external power onto VCC\_INT, all the capacitors on VCC\_INT up to the external supply voltage. I count up ~70uF on VCC\_INT.
3. External power is removed. FPF3042 detects this, disconnects Vout from Vin, and then connects Vbus to Vin (bidirectionally!). A bunch of capacitance at 12V (or more!) is then connected to VCC5P0\_USB. Yeah, C272 & C375 (10uF + 100nF) can try to absorb some of it, but it’s already charged to 5V. The rest will try to flow up the USB cable (host is probably protected), and through FR38, the ferrite bead reported as damaged.

I’m not a real EE, and don’t even play one on TV, and what I’ve described may not even be possible/damaging. But whenever my Lime shows up, I will do the following:

1. Remove USB before external power. Perhaps arrange for USB to not even provide power if I’m going to use external, that should keep the FPF3042 from ever switching over to it.
2. Keep external power low. 6V should be plenty for the board; anything more is just that much more heat being generated on the expensive SDR board.
3. Definitely be careful of the power supply attached to external power. If it has excursions above the overvoltage limit (14.2V), the FPF3042 will disconnect it (at the worst possible time!), and you’ll probably never know.

As for this fixation with how the driver doesn’t have an option to “safety eject device”, as far as I know that’s entirely there for USB storage media, where portions of the filesystem may be cached in memory. I’ve never seen it used or referenced for anything else. And I don’t see any control lines from the FX3 into the power subsystem, so there’s nothing the hardware could do the power even if you told it you were going to disconnect it.

Absent the LMS7002 needing some shutdown process (I don’t know, I haven’t read the data sheet), I don’t see what need the hardware could have for being “safely ejected”, and suspect that whole line of thought to be a distraction.

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**Author:** ![M0GLO](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/m0glo/32/999_2.png) [@M0GLO](https://discourse.myriadrf.org/u/M0GLO)\
**Post date:** [3 June 2017 17:25 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/33 "2017-06-03T17:25:19Z")

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That is the case, computers do not power down the USB port as long as the system is on and running or in he case of powered usb3 there is always power available even when the system is powered off as long as an external supply is attached to the computer.  
Disconnection via the OS is indeed just a method of forcing cache writing to avoid data corruption to storage.  
It is in short a red herring.

I do play a systems engineer in real life BTW.

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**Author:** ![BelmY](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/belmy/32/843_2.png) [@BelmY](https://discourse.myriadrf.org/u/BelmY)\
**Post date:** [3 June 2017 18:06 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/34 "2017-06-03T18:06:54Z")

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JayKominek, M0GLO,  
Thanks a lot for your contribution

I can imagine to complete a transfer (using cache) or to disable USB communication lines & power supply (if EXT is used USB is not powering) should be added some kind of HW “latching” activated by SW command.

As per MS [Article 2401954](https://support.microsoft.com/es-es/help/2401954/usb-port-remains-active-for-disabled-or-safely-removed-usb-device):

**Methods for Soft Removing a USB device**  
A USB device may be placed in a Soft Removed state by the following actions:

- Safely Removing the USB device using the Safely Remove Hardware icon in the notification area.
- Disabling the USB device in Device Manager.
- Using the SetupDiRemoveDevice API to programmatically disable the USB device.

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<div class="post-metadata">

**Author:** ![M0GLO](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/m0glo/32/999_2.png) [@M0GLO](https://discourse.myriadrf.org/u/M0GLO)\
**Post date:** [3 June 2017 19:26 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/35 "2017-06-03T19:26:45Z")

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Just so you know none of those methods actually removes power from the connectors.

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**Author:** ![BelmY](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/belmy/32/843_2.png) [@BelmY](https://discourse.myriadrf.org/u/BelmY)\
**Post date:** [5 June 2017 18:49 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/36 "2017-06-05T18:49:50Z")

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Hi JayKominek,  
I was reading again your **power supply pluging/unpluging recommendations to avoid damage to the LimeSDR board (or to the computer connected to it)** and your analysis of the automatic power source selection functionality, with the FPF3042 data-sheet in front of me (Table 1 with pin descriptions and the Truth table), and you are fully right.  
Apart from the damage risks if the sequence with a lower external voltage power supply as posible (12 V with a posible transient on 5V USB host through a “non-intended” 0.2A fuse is not desirable at all !!) is not followed, there is not need to overdissipate inside the box.

> [@JayKominek](#):
>
> But whenever my Lime shows up, I will do the following:
> 
> 1. Remove USB before external power. Perhaps arrange for USB to not even provide power if I’m going to use external, that should keep the FPF3042 from ever switching over to it.
> 
> 2. Keep external power low. 6V should be plenty for the board; anything more is just that much more heat being generated on the expensive SDR board.
> 
> 3. Definitely be careful of the power supply attached to external power. If it has excursions above the overvoltage limit (14.2V), the FPF3042 will disconnect it (at the worst possible time!), and you’ll probably never know.

Definitively this detailed information should be included in the User Manual (WARNING section), several users are asking for.

A link to the so called Magic-Power-Swapper data sheet is included:

[https://www.fairchildsemi.com/datasheets/FP/FPF3042.pdf](https://www.fairchildsemi.com/datasheets/FP/FPF3042.pdf)

Also, some specific guidelines could be added as the design between v1.2 and v1.4 (r4 or r7) boards is different for the power supply selection status (Vin\_sel, as output because EN is LOW).

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<div class="post-metadata">

**Author:** ![hTo137](https://avatars.discourse-cdn.com/v4/letter/h/ba8739/32.png) [@hTo137](https://discourse.myriadrf.org/u/hTo137)\
**Post date:** [5 June 2017 19:18 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/37 "2017-06-05T19:18:27Z")

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I’ve seen USB cords that are power-only but not sure I’ve seen data-only cords. I don’t know USB so I don’t know if a data-only is possible.

Regarding over-voltage on initial power draw with wall wart power supplies, I thought that was a typical thing with lower quality power supplies. In other words avoid cheap power supplies with expensive electronics.

Back to the OP, I see digikey no longer stocks that FR38 part but I’m sure it can be found or something that will provide same functionality. R&R (remove and replace) is another discussion. 🔍 that’s a small 0201 part. i.e. 0.03mm

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<div class="post-metadata">

**Author:** ![jslatten](https://avatars.discourse-cdn.com/v4/letter/j/f4b2a3/32.png) [@jslatten](https://discourse.myriadrf.org/u/jslatten)\
**Post date:** [3 September 2017 15:55 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/38 "2017-09-03T15:55:58Z")

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Hi, Sorry for letting this thread go dead. I’ve had a lot going on in the past several months. I measured voltage between the pin headers and I’m seeing 0.1v from GND to VCC INT and 0.0v GND to VCC Ext with only the USB cable plugged in.

I also measured from 1 side of FR38 to GND and measured 0.61v. Other side of FR38 is 0.0v.

Looks like FR38 is burned out. ☹

Not sure where else to go from here. I’d highly suggest not using external power for any others out there to ensure that this doesn’t happen to you.

Is there any way to fix the board with Lime or am I out of luck (and 289 bucks) with my damaged LimeSDR?

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**Author:** ![Ancer](https://avatars.discourse-cdn.com/v4/letter/a/278dde/32.png) [@Ancer](https://discourse.myriadrf.org/u/Ancer)\
**Post date:** [4 September 2017 02:23 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/39 "2017-09-04T02:23:09Z")

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@jslatten

FR38 looks like coil try jumper it with small wire see if your card will power up.

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<div class="post-metadata">

**Author:** ![jslatten](https://avatars.discourse-cdn.com/v4/letter/j/f4b2a3/32.png) [@jslatten](https://discourse.myriadrf.org/u/jslatten)\
**Post date:** [4 September 2017 16:43 UTC](https://discourse.myriadrf.org/t/external-power-supply-damaged-board/1207/40 "2017-09-04T16:43:56Z")

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I tried to jump it but no luck. Still no power. I don’t see any obvious damage to any other components but may just be missing something.

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