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GeorgeGR
Posts: 5
Joined: Wed Mar 02, 2016 12:32 pm

SOLVED - CM Custom PCB power problem?

Fri Mar 04, 2016 10:15 am

First of all, Hi everyone.

I am developing a PCB for a client to interface the CM with an industrial installation.

My design uses a quite complex PSU design but using off the self step-up/down modules i keep it as simple as possible.
Schematics
(The UPS part is realized using Super Capacitors.)

In this version of the PCB there was a footprint mismatch with the soDIMM socket an it is hand soldered and for this the pins 1 through 39 (odds only) are not soldered (and removed from the socket).
CM Gen PSU_1.jpg
CM Gen PSU_1.jpg (62.05 KiB) Viewed 1544 times
CM Pi+Com PSU_1.jpg
CM Pi+Com PSU_1.jpg (56.91 KiB) Viewed 1544 times
CM Ready to use8_55_85.jpg
CM Ready to use8_55_85.jpg (57.21 KiB) Viewed 1544 times
- PROBLEM #1 (possibly same reason as #2)
To correctly boot the CM the PCB should be unused for several hours or discharged the capacitors (super and small electrolytic), fired up for a second or two and then reseted.

-PROBLEM #2
After booting and log in through serial console everything works ok until first halt/poweroff/reboot. When happens one of these the CM is fried. After testing the pins one by one I figured out that the GPIO0-27_VREF is shorted to Ground!
Four (4) times happened 4 modules dead.

So... can anyone suggest anything that will help?
I am waiting some new modules today but I can't afford to destroy any more.
Last edited by GeorgeGR on Thu Mar 10, 2016 10:13 am, edited 1 time in total.

hasseb
Posts: 17
Joined: Wed Dec 24, 2014 3:03 pm

Re: CM Custom PCB power problem?

Fri Mar 04, 2016 8:18 pm

Should you have some 5 volts input for your CM? Pins 197, 198, 199, 200?

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GeorgeGR
Posts: 5
Joined: Wed Mar 02, 2016 12:32 pm

Re: CM Custom PCB power problem?

Sun Mar 06, 2016 12:03 am

hasseb wrote:Should you have some 5 volts input for your CM? Pins 197, 198, 199, 200?
https://www.raspberrypi.org/documentati ... ematics.md

hasseb
Posts: 17
Joined: Wed Dec 24, 2014 3:03 pm

Re: CM Custom PCB power problem?

Mon Mar 07, 2016 11:12 am

Still it sounds like a powering issue. I think it is not very good idea to use a single 3.3V power supply for VBAT and 3V3. Is you supply strong enough to provide at least 3 watts of constant power?

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GeorgeGR
Posts: 5
Joined: Wed Mar 02, 2016 12:32 pm

Re: CM Custom PCB power problem?

Mon Mar 07, 2016 12:34 pm

The compute modules booted correctly on the CMIO board with an HDMI display connected which i don't use in my implementation.
The CMIO board uses the PAM2306AYPKE that supports up to 1A output for each channel (3v3 & 1v8).
I use the LXDC3EP33F-204 which also supports 1A output (only 3v3, i use a separate DC/DC for the 1v8).

Update: When I power my PCB (with or without a CM on) I noticed that sometimes the 1v8 line latches to overcurrent mode.
So it looks like it is a power issue but with the 1v8 line that has a 250mW requirements as the CM-Design Guide notes
(I use the LXDC2HN18A-097 which outputs 600mA MAX and typical OC latch mode at 900mA).
https://www.raspberrypi.org/documentati ... gnguide.md
But without a CM in place, the only line that is powered with 1v8 is the pull-up of the Activity LED MOSFET's driver gate (GPIO47_1v8).
In one PCB the input Capacitor of the 1v8 line was also shorted.

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GeorgeGR
Posts: 5
Joined: Wed Mar 02, 2016 12:32 pm

Re: CM Custom PCB power problem?

Tue Mar 08, 2016 9:19 am

All suggestions will be appreciated :)

User avatar
GeorgeGR
Posts: 5
Joined: Wed Mar 02, 2016 12:32 pm

Re: CM Custom PCB power problem?

Thu Mar 10, 2016 10:12 am

Solved!
Bad soldering of the so-DIMM socket.

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