[j-nsp] T4000 power architecture

[Sam Silvester]

Bumping for good measure...

So JTAC are suggesting it's either the PEM or the midplane, but I was
hoping to get some more information so I can validate what I'm being told -
which, currently, is very little. Basically the suggestion is "replace the
PEM, if that doesn't work replace the chassis". I'd like to avoid
whack-a-mole if possible; for example, if I knew that all of the FPCs were
fed via the PEM via a central bus on the midplane, then we don't have to
worry about replacing the PEM and can go straight ahead with organising a
chassis swap.

I don't suppose somebody happens to have a spare T4000 chassis or PEM lying
around and could take a photo of the connectors between the PEM and the
midplane? I'm still trying to get an idea of how power is distributed from
the PEM to the actual FPC slots.

The exact same questions has been posed to JTAC multiple times, but no
answer has been forthcoming. I really hope the nagging suspicion I have
that nobody in Juniper knows this information is incorrect but in the
meantime I'm posting here in the hope I can figure it out from some
pictures.

Google image search isn't helping me find any clear photos of the rear of
the PEM or the midplane :/

Sam


On Thu, Sep 11, 2014 at 8:06 AM, Sam Silvester <sam.silvester at gmail.com>
wrote:

> Hi Aqeel - thanks for the reply.
>
> Agree 100% - the problem is, we only seem to be getting power to FPC0 from
> one PEM... have a look below (and also note that FPC1 is fine, as are the
> rest of the FPCs).
>
> The question is - are we looking at a PEM fault here, or a midplane fault?
> As per previous discussion, the FPC itself seems fine, as moving it to
> another slot resolves the issue. Putting another card into slot 0 yields
> the same result as below.
>
> PEM 0 status:
>   State                      Online
>   Temperature                32 degrees C / 89 degrees F
>   DC Input:                  OK
>                       Voltage(V)  Current(A)  Power(W)  Load(%)
>       INPUT 0           54.750       4.312      236        9
>       INPUT 1           54.500       6.000      327       13
>       INPUT 2           54.625      11.750      641       26
>       INPUT 3           54.750       6.125      335       13
>       INPUT 4           54.250      10.500      569       23
>       INPUT 5           54.500       6.062      330       13
>   DC Output           Voltage(V)  Current(A)  Power(W)  Load(%)
>       FPC 0             55.062       8.625      474       31
>       FPC 1             55.250       4.062      224       14
>
> <...snip...>
>
> PEM 1 status:
>   State                      Online
>   Temperature                30 degrees C / 86 degrees F
>   DC Input:                  OK
>                       Voltage(V)  Current(A)  Power(W)  Load(%)
>       INPUT 0           54.500       3.250      177        7
>       INPUT 1           54.625       3.375      184        7
>       INPUT 2           54.500      12.437      677       28
>       INPUT 3           54.500       5.125      279       11
>       INPUT 4           54.625      12.062      658       27
>       INPUT 5           54.375       2.750      149        6
>   DC Output           Voltage(V)  Current(A)  Power(W)  Load(%)
>       FPC 0              0.000       0.000        0        0
>       FPC 1             55.125       4.500      248       16
>
> <...snip...>
>
>
>
> On Wed, Sep 10, 2014 at 8:48 PM, aqeel ahmed <aqeelpk at yahoo.com> wrote:
>
>> Hi
>>
>> Though aimed for redundancy If system has both power supplies installed
>> then it will automatically load balance and in case one power supply goes
>> down then whole system will be on single power supply left working.
>>
>> For further details you can refer to following juniper document.
>>
>>
>> http://www.juniper.net/techpubs/en_US/release-independent/junos/information-products/topic-collections/hardware/t-series/t4000/hwguide/t4000-hwguide.pdf
>>
>> Regards
>>
>>
>>
>>   On Wednesday, September 10, 2014 5:16 AM, Sam Silvester <
>> sam.silvester at gmail.com> wrote:
>>
>>
>> Howdy,
>>
>> Can anybody shed any light on how the PEMs on a T4000 actually distribute
>> power to each FPC slot?
>>
>> Have the case of a single FPC slot that is showing power being received
>> from only one of the PEMs, whilst all the other FPC slots are load sharing
>> as expected.
>>
>> Replacing the FPC shows the same issue, so we're pretty happy that it's
>> "slot specific".
>>
>> What I'm curious about is if the midplane has individual 'traces' (for
>> lack
>> of a better term) for supplying power to each FPC from the two PEMs, or if
>> there is a common bus shared between all the FPCs from each PEM. The
>> reason
>> I ask is if the PEM only has a single connection to the midplane,
>> replacing
>> it seems pointless and instead it looks like we're better off replacing
>> the
>> midplane. If the PEM has individual outputs to each slot, then replacing
>> the PEM seems like a reasonable approach.
>>
>> I've been pointed at the following document (
>>
>> http://www.juniper.net/documentation/en_US/release-independent/junos/topics/concept/power-supply-t4000-description.html
>> )
>> which is very light-on in terms of detail. Does anybody know if there is a
>> more detailed document available (or even internally?) that we can ask
>> about?
>>
>> Thanks!
>> _______________________________________________
>> juniper-nsp mailing list juniper-nsp at puck.nether.net
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>>
>>
>>
>