User avatar
RiccardoMoretti
Posts: 65
Joined: Fri May 25, 2012 5:33 am

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

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23311
Joined: Sat Jul 30, 2011 7:41 pm

Re: Missing labels on the schematics 4b

Tue Jun 25, 2019 7:13 am

No idea, will check.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
"My grief counseller just died, luckily, he was so good, I didn't care."

User avatar
RiccardoMoretti
Posts: 65
Joined: Fri May 25, 2012 5:33 am

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
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 117
Joined: Wed Mar 19, 2014 2:58 pm
Location: Cambridge

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?
James Adams
Raspberry Pi - COO & Hardware Lead

User avatar
RiccardoMoretti
Posts: 65
Joined: Fri May 25, 2012 5:33 am

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
Posts: 5757
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

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 ?

User avatar
RiccardoMoretti
Posts: 65
Joined: Fri May 25, 2012 5:33 am

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 ?

Return to “Advanced users”