Pynq Z1: Is power regulator toast?

[nickcamel]

I had started the Pynq Z1 3 times, having had it up and running at maximum 20min, the fourth time I try to start it.. nothing.. I mean no red led, no nothing. Changed jumpers from REG to USB and powered up, momentarily, then it rebooted again. So it was now stuck in a boot loop. I lose the debug port at reset, so I had to connect manually an instance later, trying to log what is happening and why it's rebooting.

It seems it reboots at random point during startup, sometimes, it survives all the way to login, only to reboot seconds later. I've trying USB power from my laptop, USB hub (external power) and my laptops docking station.. same behaviour. (Reflashed the sd card.. same behaviour)

So I went back to investigating why the external power supply (OEM) wouldn't give power to the board. (I measured on power supply pin and it's 12V)

I found this that IC25 doesn't look too well. How could this happen?

Does anybody know if this IC25 has anything to do with the power supply or if I'm facing multiple problems here?

Thanks!

[xc6lx45]

Hi,

just a common sense answer. This is a case for Digilent or vendor support as the board is obviously broken. 

IC25 is a power supply component, regulator from 5 V to 3.3 V for analog.

Schematic, see here "sheet #13 out of 13" C2 quadrant:

https://reference.digilentinc.com/_media/reference/programmable-logic/pynq-z1/pynq-z1_sch.pdf

Most likely it's shorting 5V and causing trouble indirectly.

Assuming I'm not paying for the stuff I'd simply unsolder it (and lose the analog filtering capabilities) but that will void your warranty. Just a thought, please check the schematic for implications as I just did a cursory search for the dependent "analog" 3.3 V supply.

 

[nickcamel]

5 minutes ago, xc6lx45 said:

Hi,

just a common sense answer. This is a case for Digilent or vendor support as the board is obviously broken. 

IC25 is a power supply component, regulator from 5 V to 3.3 V for analog.

Schematic, see here "sheet #13 out of 13" C2 quadrant:

https://reference.digilentinc.com/_media/reference/programmable-logic/pynq-z1/pynq-z1_sch.pdf

Most likely it's shorting 5V and causing trouble indirectly.

Assuming I'm not paying for the stuff I'd simply unsolder it (and lose the analog filtering capabilities) but that will void your warranty. Just a thought, please check the schematic for implications as I just did a cursory search for the dependent "analog" 3.3 V supply.

 

Thanks alot for finding that schematics! Glad too see it is in fact related to my power problem. With this finding there's no doubt we should contact vendor directly.

A thought: in the schematics there are 2 + 2 pins, whereas on my IC25 chip, there are 2 + 3 pins. Has it maybe anything to do with version?

[xc6lx45]

no, it looks just like in the datasheet. 

https://www.ti.com/lit/ds/symlink/lp5907.pdf?ts=1609885581480&ref_url=https%3A%2F%2Fwww.google.ru%2F

page 34 "SOT 23"

and just to make it clear (referring to the subject line) it's not a capacitor but a linear regulator.
If I had to make a bet what killed it, I'd suspect potential issues between the power supply and any other "ground" that was connected to the board.

[nickcamel]

Yeah ok, pin 4 isn't shown in schematics, but is in TI's docs. Thanks, again.

(changed topic to "power regulator" lol, "linear regulator" seems like the type of term people that know what they are talking about would use)

Other grounds would only be through ethernet and usb, both connected to "certified" (don't know how else to put it) devices, since power supply that ships with board doesn't connect to ground from wall outlet. Both ethernet and usb cable was in the package. So..what? My router and/or PC is to blame?

[xc6lx45]

Well, I doubt you'll find a satisfying answer to the root cause. If you aren't aware of any abuse, I'd put it down on bad luck.

Ethernet is transformer coupled and isolated (other than 1 nF, see "circuit A" here https://www.mouser.de/datasheet/2/706/fastjack-gigabit-520265.pdf) so you can probably rule that out. 

>> since power supply that ships with board doesn't connect to ground from wall outlet

Actually this is where things get complicated. You can't have perfect isolation between primary and secondary sides of the power supply because this would allow static charge to build up without limit and eventually destroy the circuit. What's typically done (I have not studied this specific PSU) is to put in a high-impedance voltage divider (many megaohms) that puts the secondary side effectively at 50 % of the mains voltage. So much for "ground" ... This is e.g. the "buzz" you can feel from many laptops running on AC power. This is usually safe since the current is limited but then components break and no one understands why.

It can help to ground the circuit on my desk properly (e.g. any self-respecting lab power supply has a "GROUND" pin) and make sure that this ground connects first and disconnects last with respect to any two-pin wall-wart power supplies. But this doesn't remove the problem, just makes it appear in a controlled, repeatable manner. 

 

 

[Bianca]

Hello,

That part has an absolute rating of 6V. The fact that it happened when you switched from REG to USB makes me think that the USB power supply/HUB you were using might have provided a higher voltage. When using the REG, the 5V is created by another power supply, so as long as the 12V power supply you are using is fine, the board should work without problems, and no damage can be done to the board. 

However, when you power it via USB, the voltage is not limited by anything. If your USB is capable of giving more that 5V by design, (for example Samsung chargers are capable of providing 5V and 9V. The voltage negotiation is done by Samsung devices. Someone tried to power one of our boards with a Samsung charger, it worked for a couple of times, and then it burned the board) or by defect, some components might get damaged. 

That component though, received some significant damage so I am not sure it was caused by a slightly over voltage. It might also be a component manufacturing defect that caused it to fail quickly. 

I will private message you for some details regarding your purchase/warranty and see what can we do about it. 

 

Regards,

Bianca

[nickcamel]

@Bianca Thanks for your reply.

Just to note, I did only switch to USB *after* the board stopped responding/getting turned on using REG with power supply.