Editing IBM RS/6000 Maintenance Guide (section)

== PSU Voltage Checks ==

'''A caution before you measure anything.''' The RS/6000 spans fifteen years and several supply architectures, from Micro Channel deskside units to hot-swap rack supplies, and '''IBM publishes per-rail tolerances for none of them in any document this wiki has located'''. The table that used to sit here gave one set of "typical" figures for the whole family, described the supplies as "ATX-like" (which the Micro Channel machines' are not), and put the negative rails at &plusmn;5 % when even the ATX specification allows &plusmn;10 %.<ref name="atxspec">Intel, ''ATX / ATX12V Power Supply Design Guide'', the specification these supplies are built to. It sets '''&plusmn;5 per cent''' on +3.3 V, +5 V, +12 V and +5 VSB, and '''&plusmn;10 per cent''' on &minus;5 V and &minus;12 V. The figures in this table are the specification's, not IBM's: IBM does not publish per-rail tolerances for these machines, and the supplies are bought-in industry-standard units.</ref> It has been removed.

What to do instead:

* '''Identify the supply from its own label''', then find the matching service guide &mdash; SA38-0512 and SA38-0531 cover ranges in this family.
* '''Read the rails the supply itself claims''' off that label and measure against them.
* On the later PCI machines the supplies are close to industry-standard parts and the ATX bands are a reasonable sanity check; on 7011, 7012, 7013 and 7015 they are not.
* '''A rail that is present but sags under load and recovers when cards or drives are pulled''' tells you more than any tolerance table.

IBM does publish machine-level power figures, which are useful for sizing and for spotting an overloaded supply:

* '''7026-H70''' — 750 W PSU, FC 6290.<ref name="s5a71b0">[https://www.amazon.com/IBM-6000-7026-H70-POWER-SUPPLY/dp/B000MRECHI Amazon listing &mdash; B000MRECHI] A retail listing, used only to establish that the part exists and its rating. Not a technical source.</ref>
* '''7015 R10 / R20 / R21''' CPU drawer — 0.29 kVA typical, 200–240 V AC.
* '''7015 R24''' — 0.685 kVA typical, 200–240 V AC or −48 V DC.
* '''Per-machine watts for 7011, 7012, 7013, 7043''' — refer to SA38-0531 / SA38-0512.