Mostly Dead Parallella

[geniass]

Hi all,
I recently bought a Parallella Desktop off Amazon while in the US. Having arrived back in South Africa, I now know that it hardly ever powers on. I have described the problem already on the Parallella forums (http://forums.parallella.org/viewtopic.php?f=50&t=2182&sid=201d895ebd82772ed6ea1b6d45c10b20) but I haven't received any  suggestions that helped much. Anyway what happens is that when I power on the board, the POWER-ON LED lights up, but another LED which should light up doesn't. Even the UART does nothing. Here are the board's design files as well: https://github.com/parallella/parallella-hw/tree/master/boards/parallella-I.

Now Amazon won't refund me and Adapteva haven't replied to my support emails, so my only option is the try fix it myself. So far I have tested the input voltage (5.16V; correct) and fuse F1 is intact. I have also tested all the output voltages from the DC-DC converters on Page 16 of the schematic.

Can anyone recommend what I can try next? I don't know if tracing all the voltages is feasible since I can hardly see some components and they aren't all marked.

Thanks, hopefully I can finally get an answer here.

[PA0PBZ]

Are you sure you created the bootable SD card correctly?

[geniass]

It's failing long before the SD card is involved. Usually there is no output on the UART but after every few hundred tries it actually does boot up. It's just completely unpredictable.

[PA0PBZ]

Allright. I've never seen or used one but from what I could find from a quick search it needs an SD card to boot. Clearly it boots from something else before that.
First thing to check with these kind of stability problems is power supply, but I see you already covered that. Did you visually inspect the PCB trying to find any irregularities?

[wraper]

First check if reset circuit(s) work correctly.

[geniass]

It uses U-boot as the bootloader which is meant to output to the UART before it reads the SD card.

I will check the power supply with an oscilloscope tomorrow but I doubt that's the problem since I have tried 3 different ones.

Also the board looks completely normal to me, although it would be easy to miss a bad solder joint or something. On my version of the Parallella there actually is no reset switch (SW2 is unpopulated) because it wouldn't fit under the heatsink, but I tried manually shorting SW2 with no effect.

[PA0PBZ]

I tried manually shorting SW2 with no effect.

Did you check the levels at pin 1 and 4 of U33? (Page 17) They should toggle when you press and release the reset button.

[geniass]

Just measured it: when SW2 is shorted pin 4 drops from 1.72V to 0V then back to 1.72V which seems right to me. It's about a 300ms pulse.

[Rasz]

I will check the power supply with an oscilloscope tomorrow but I doubt that's the problem since I have tried 3 different ones.

nooo, check power supplies on the pcb, there will be a few (3.3, 2.5, maybe even lower ones for fpga)

[geniass]

Yes I measured all the DC- DC outputs on page 16 and they are all fine.