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RiccardoMoretti
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Missing labels on the schematics 4b

Tue Jun 25, 2019 7:08 am

I'm looking at the schematics for the Pi 4b and whilst the information is there, you have no Idea what chip is being referred to, i see the other documents have the labels on,
Was this intentional or an omission ?

https://www.raspberrypi.org/documentati ... educed.pdf

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Re: Missing labels on the schematics 4b

Tue Jun 25, 2019 7:13 am

No idea, will check.
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RiccardoMoretti
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Re: Missing labels on the schematics 4b

Tue Jun 25, 2019 8:18 am

Thanks James,
just to clarify my initial post and to help you,

the previous docs had the component part number or its label
EG,

10103594-0001LF Power In
1-1734248-5 Display
XR77004 U8
A70-112-331-N126 J10 Ethernet

James Adams
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Re: Missing labels on the schematics 4b

Tue Jun 25, 2019 10:24 am

These have been removed as they aren't generally useful - they aren't standard parts that are available in the channel and so you can't get hold of the parts or datasheets.

Also, we often change manufacturers (of connectors, say) so they can change over time.

Is there some specific info you need?
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RiccardoMoretti
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Re: Missing labels on the schematics 4b

Tue Jun 25, 2019 11:38 am

All good many thanks, I just wasn't sure of the power management chip (MxL7704) but I did find a picture of the Pi and I saw the part number from there, just would have been nice to see that on the schematic

hippy
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Re: Missing labels on the schematics 4b

Tue Jun 25, 2019 12:02 pm

RiccardoMoretti wrote:
Tue Jun 25, 2019 11:38 am
All good many thanks, I just wasn't sure of the power management chip (MxL7704) but I did find a picture of the Pi and I saw the part number from there, just would have been nice to see that on the schematic
I agree. It may not be that useful for most people but is useful for some, but not that useful when the parts are proprietary and datasheets are not available.

Knowing what parts were originally used and what is actually fitted has been useful in identifying some issues which have arisen when parts have changed. This was the case when a replacement regulator made a Pi much more sensitive to small 5V drops than it previously was.

It also allows people to double-check that everything is how it should be, identify issues there may be, as might have been the case with the PoE HAT issue.

Knowing the part numbers is also useful for figuring out what the lowest voltage a Pi can run at is, though that's complicated by not having full circuit diagrams as well as not having datasheets.

Talking of 'wanting to know': Can anyone read the part number of the Boot Eeprom on a Pi 4 ?

I'm guessing it's the chip near the GPIO on the rear of the board given the solder pad jumpers -

https://raspi.tv/wp-content/uploads/201 ... _700-1.jpg

Thoygh it might be one of the two 8-legged chips to the lower left of the VIA USB chip -

https://raspi.tv/wp-content/uploads/201 ... 4B_700.jpg

I was thinking the Boot Eeprom could be used to hold Videocore bare metal code, so one can have an entirely embedded Pi system bootable without any SD Card or anything else connected. But to pursue that it would be useful to know its write-erase lifetime and for that one needs to know the part number. I haven't so far found a photo which I can read that on, and that's not even included on the schematics.


One thing which does intrigue me on the Pi 4B schematic is what "WB_VBAT" is used for ?

Could "WB" be Watch Battery ? Or Something Backup ?

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RiccardoMoretti
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Re: Missing labels on the schematics 4b

Tue Jun 25, 2019 3:06 pm

hippy I agree with you,
It's exactly why I wanted the see the IC part number, so I could read the data sheet, which is available. having U8 on the schematic is way more useless to me!
https://www.maxlinear.com/ds/mxl7704.pdf

I can see there has been a revision to the mxl7704 IS from 03 to 04

WB could that refer to Wireless/Bluetooth ?

chrisnz
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Re: Missing labels on the schematics 4b

Fri Oct 18, 2019 10:43 am

hippy wrote:
Tue Jun 25, 2019 12:02 pm
One thing which does intrigue me on the Pi 4B schematic is what "WB_VBAT" is used for ?
I too am curious as to what this net is for.

It's connected to 5V via a diode and supplies power to the power led.

Strangely, the LED is turned off by shorting it out - kind of weird.
Also of concern is the 470R R13, which appears to do nothing but sit there and burn 10mA for no apparent reason.
With GLOBAL_EN shorted to ground, turning off the PMIC, the LED and R13 appear to be the only things consuming power.
I get 22.2mA in power-off mode and 13.9mA when GLOBAL_EN is at 0V. The LED is consuming 3mA, due to its 1.8V drop and a 1K resistor. R13 must be taking the other 10mA.

What would be the harm in removing R13, or replacing it with a higher value? Is WB_VBAT connected to anything else? From the top and bottom layers it looks like it's not, but obviously I can't see the inner PCB layers and the foundation is shy on releasing more detailed schematics for some unknown reason.
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trejan
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Re: Missing labels on the schematics 4b

Fri Oct 18, 2019 12:05 pm

hippy wrote:
Tue Jun 25, 2019 12:02 pm
Thoygh it might be one of the two 8-legged chips to the lower left of the VIA USB chip -

https://raspi.tv/wp-content/uploads/201 ... 4B_700.jpg
Boot EEPROM is a Winbond W25X40CLUXIG. It is the USON-8 closest to the headphone socket.

USB controller EEPROM is a Winbond W25X10CLUXIG. It is the USON-8 closest to the USB controller.

Manufacturer/Device ID and markings match up with the Winbond datasheets. Both parts are rated for > 100,000 erase/write cycles.

hippy
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Re: Missing labels on the schematics 4b

Fri Oct 18, 2019 12:48 pm

chrisnz wrote:
Fri Oct 18, 2019 10:43 am
Is WB_VBAT connected to anything else? From the top and bottom layers it looks like it's not, but obviously I can't see the inner PCB layers
There are these, but not sure they will be a lot of use ...

https://www.raspberrypi.org/app/uploads ... tW8Qws.jpg

https://imgur.com/a/Y6mtR2E#A8ud1e6

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