christopherlange1110
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rpi3 resistor help

Sat Nov 05, 2016 8:40 pm

I am trying to find a value of a resistor that fell off my pi3. If anyone can please measure the value of r31 next to the x1 crystal it woud help me revive my board.

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DougieLawson
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Re: rpi3 resistor help

Sat Nov 05, 2016 8:43 pm

I can fix your RPi for you, it's going to cost about £35 to do that.
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christopherlange1110
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Re: rpi3 resistor help

Sat Nov 05, 2016 8:55 pm

Well that's rude? I can fix it I have smt resistors, hot air station and skill to use it. I just wanted to know the value. I mean can't you measure one of your own with a meter? That's helping someone. Not "I can fix it for you it will be 35 dollars". If I knew I could not fix it myself I would buy a new one but its a resistor not a soc or wifi chip. Aren't we suppose to be helping people? That's what this forum is for an't it? Not promoting more sales of boards?

gregeric
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Re: rpi3 resistor help

Sat Nov 05, 2016 8:57 pm

Are you sure R31 is the only damage?

On the Pi2, R31 also lies bottom side, but underneath the LAN9514, with one end clearly connected to PP28 (LAN 25MHz clock).

Component part numbering & function seems to be consistent across the modern (40 pin header) Pi model Bs. With R31 it missing, I would expect the Pi to boot from SD, but without working USB /LAN.

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johnb_summers
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:01 pm

christopherlange1110 wrote:Well that's rude? I can fix it I have smt resistors, hot air station and skill to use it. I just wanted to know the value. I mean can't you measure one of your own with a meter? That's helping someone. Not "I can fix it for you it will be 35 dollars". If I knew I could not fix it myself I would buy a new one but its a resistor not a soc or wifi chip. Aren't we suppose to be helping people? That's what this forum is for an't it? Not promoting more sales of boards?
But he would have added some pink ponies and unicorns, and its £35 English pounds and I think that's about $6000 in dollars or there about, don't know never seen a dollar, think they use them in monopoly or in loos.
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B.Goode
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:03 pm

You'll have to make allowances for @Dougie. He has got so used to not helping people in the nearly 24k posts he has made that it will take us a while to retrain him...

The assumption might have been unjustified, but surely you can see that most people would not have a clue about smt components and the technology needed to solder them?

christopherlange1110
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:07 pm

Yea since it fell off i have no usb or ethernet. Its on a rpi3. Thanks for help.

gregeric
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:17 pm

I don't have my 'meter at hand to test, but I suspect R31 is a series termination resistor of a few 10s of Ohms (could well be wrong on that).

It may be the case that the same R31-sourced clock is used for the BCM43438 WiFi/BT combo chip; that would explain your lack of WiFi reported here: viewtopic.php?f=28&t=164895&p=1063833#p1063833

christopherlange1110
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:21 pm

gregeric wrote:I don't have my 'meter at hand to test, but I suspect R31 is a series termination resistor of a few 10s of Ohms (could well be wrong on that).

It may be the case that the same R31-sourced clock is used for the BCM43438 WiFi/BT combo chip; that would explain your lack of WiFi reported here: viewtopic.php?f=28&t=164895&p=1063833#p1063833
Yea that was before I found the missing resistor. Could it be part of the power to the lan/usb and wifi/bt subsystem.I can use a redbear wifi hat and it works and connects. It is also causing the undervolt warning to show on the screen.
Last edited by christopherlange1110 on Sat Nov 05, 2016 9:25 pm, edited 1 time in total.

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johnb_summers
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:23 pm

the circuit diagram is here https://www.raspberrypi.org/blog/model- ... chematics/ but that the 2 not the 3 and all my 3's are in cases and a pain to get out.
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gregeric
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:30 pm

johnb_summers wrote:the circuit diagram is here https://www.raspberrypi.org/blog/model- ... chematics/ but that the 2 not the 3 and all my 3's are in cases and a pain to get out.
That is the circuit diagram of the original (Pi1) model B, Rev2, 26-pin header variant Pi. No full schematic for 40-pin header Pi has been released.

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aTao
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:31 pm

from https://www.raspberrypi.org/documentati ... matics.pdf R31 goes from +3.3V to pin 41 of the LAN9512 ic signal:AUTOMDIX_EN value 10k
It would seem that the drawing is valid unless there are updates on https://www.raspberrypi.org/documentati ... EDUCED.pdf which there arent for this component.
>)))'><'(((<

christopherlange1110
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Re: rpi3 resistor help

Sat Nov 05, 2016 9:42 pm

aTao wrote:from https://www.raspberrypi.org/documentati ... matics.pdf R31 goes from +3.3V to pin 41 of the LAN9512 ic signal:AUTOMDIX_EN value 10k
It would seem that the drawing is valid unless there are updates on https://www.raspberrypi.org/documentati ... EDUCED.pdf which there arent for this component.
Yea i went all over the drawing. From what i can see it is connected with vias to the middle of the board. I have a pi 2 and that resistor is not there.. Also found out i controls the act led too. i believe it is part of the power control system. Thanks for all of yalls help!!!

sparkyhall
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Re: rpi3 resistor help

Sat Nov 05, 2016 10:21 pm

I just measured R31 as zero Ohm on my Pi3.

gregeric
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Re: rpi3 resistor help

Sun Nov 06, 2016 8:44 am

aTao wrote:from https://www.raspberrypi.org/documentati ... matics.pdf R31 goes from +3.3V to pin 41 of the LAN9512 ic signal:AUTOMDIX_EN value 10k
It would seem that the drawing is valid unless there are updates on https://www.raspberrypi.org/documentati ... EDUCED.pdf which there arent for this component.
I think the 40-pin Pis were a clean-slate redesign - component designations are not consistent on the Pi 1 schematics with what I see on boards from the B+ onwards. The LAN951x section in particular got some rethinking - gone was its own crystal, instead getting its clock (ETH_CLK) from the SoC. As I mentioned above, one end of R31 goes to PP28, which is quoted as being ETH_CLK.

Heater
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Re: rpi3 resistor help

Sun Nov 06, 2016 9:34 am

Yep, my Fluke tells me R31 on my Pi 3 is zero ohms. It's just a jumper.

So if you can bridge those old pads you are in business.

Else it's take up Dougie on his repair offer. Which would actually be cheap compared to what I have paid for Pi 3 around here !
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DougieLawson
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Re: rpi3 resistor help

Sun Nov 06, 2016 10:27 am

It's £35 + time & materials + p&p + VAT.
Any language using left-hand whitespace for syntax is ridiculous

Any DMs sent on Twitter will be answered next month.
Fake doctors - are all on my foes list.

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johnb_summers
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Re: rpi3 resistor help

Sun Nov 06, 2016 11:15 am

DougieLawson wrote:It's £35 + time & materials + p&p + VAT.
Don't forget the pink ponies and unicorns
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bensimmo
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Re: rpi3 resistor help

Sun Nov 06, 2016 11:24 am

Dougie is expensive, DIY for £31.99 delivered at Amazon or Currys/PC World ;-)

christopherlange1110
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Re: rpi3 resistor help

Sun Nov 06, 2016 4:53 pm

Cool! I have a reel of 10k resistors of the same size. I measured the voltage on the pads and got 3.3v on one side. So just to be safe I'll try a resistor first then if that causes gremlins then I'll jump the pads. It's weird issues to without the component there. The board will boot into a gui but the act led is not working along with Ethernet WiFi/Bluetooth and USB. Also shows undercoat on screen and the power led stays on suppose to be off in a undercoat situation. Thanks for all the help people. Also I'm in the US so these boards are not cheap though around 40 bucks and have to wait 2 weeks to get one. Lol!

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