expert opinion needed on Raspberry Pi power issue

Mike Powell pinged me this thread directly and asked if I could respond, first apologies dropping of the radar (is it really that long!).  I have been looking at board bugs and this one is on my list, notes in my lab so more tomorrow.

All - it would be really helpful if you could call out your serial numbers, it would allow me to find one in my stash with (hopefully) the same batch of parts, then we can get test aligned.

Pete

Hi Pete,

Serial number from the SoC or the label on the back of the board ?  The one I started modifying is labelled FN120711618 & SoC serial 000000001395836f not sure which number is more useful.

Hi Selsinork

The FN number is the one, unfortunately my stash of boards runs out at FN120651352 so if the serial number are 'really' sequential you are 60K boards later than mine. [In reality we get a hole when the month changes so it's hard to predict exactly.] I'll call in some more testing samples from our partners.

The warmest SMSC I have is 54C at T-ambient of 29C which is a deal cooler than the 61C reported.  There must be a corner case where RG1 is regulating low and the SMSC regulating high (as already suggested).  Time to ping off RG1 on a few more boards and see if I can kill one or get it to misbehave.

On the case....

Cheers

Pete

If it helps, my warm board with the elevated 1.8v is FN120744907

Removing RG1 did seem to make it quite a bit hotter

Hi Troy - thanks for that

Do you have any way of measuring this - I would also be interested in the 1V8 voltage with RG1 off.

Cheers

Pete

This particular board which was noticeably warmer than my others but not exceptionally hot was measuring 1837mV before and after (compared to 1793mV on another board). Measurement was taken across the RG1 common and output pads. Sorry, I don't have a way of accurately measuring temperature, only my finger.

This particular board which was noticeably warmer than my others but not exceptionally hot was measuring 1837mV before and after (compared to 1793mV on another board). Measurement was taken across the RG1 common and output pads. Sorry, I don't have a way of accurately measuring temperature, only my finger.

Troy

After years of soldering, I sort of got used to holding on to parts even though I knew they were burning my fingers as I would only need to resolder it again.  The advent of lead free has elevated the pain barrier again!

So to be sure - you are saying that with RG1 out of the circuit and the SMSC providing all the power, the voltage was 1837mV and the same with RG1 reconnected?

If any of the other 'hot runners' reading this thread could just measure the 1V8 that would be great, in fact anyone who could report, hot or warm and the voltage would be tremendously useful. {Don't forget serial numbers from the white label on the underside]

Pete

Yes, I measured 1837mV before and after removing RG1, however it did get quite a bit hotter with RG1 off. Just to clarify what I said in the other thread, this is the second board I have taken to with the iron. The first one was fine (aside from a little instability, which is probably software related and me expecting too much) and I couldn't get it really hot even without RG1. The only modification made to this one was removing and replacing RG1.

Hi Pete,

  It's good to see you back in this forum. 

I'm curious if you have enough data to tell if the temperature

distribution between different boards is normal (bell curve) or

bi-modal (hot boards and merely warm boards, but not much

between).

I'm also curious if you think the 80mA current that Mackay measured

at RG1 during startup would be enough to account for the observed

temperature differences.

followups can go to the other thread.