Editing Macintosh SE/30 Troubleshooting (section)

=== Power Rails ===

The logic board takes power and video through '''J12''', Apple's "Power & Video Connector", a 14-way header. The pinout below is from Apple engineering drawing 050-0253-01 as redrawn by the ''macse30mlb'' project, and has been checked pin by pin against that schematic.<ref name="se30sch" />

{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+ '''J12 — power and video connector'''
|-
! Pin !! Signal
|-
| 1–5 || Ground
|-
| 6 || −5 V
|-
| 7 || −12 V
|-
| 8 || Ground
|-
| 9 || Video out
|-
| 10 || Horizontal sync
|-
| 11 || Vertical sync
|-
| 12, 13 || +5 V
|-
| 14 || +12 V
|}

That pinout makes bench-powering a bare logic board practical, and it tells you what each rail is for:

* '''+12&nbsp;V (pin 14)''' feeds the internal and external floppy drives, the PDS connector and the sound circuit — J6, J8, J13 and UB10/UB11/UA9. A board will come up to a point without it, '''but the sound chip UB11 will hold the system in reset''', so the furthest you will get is horizontal lines or a simasimac screen.
* '''−12&nbsp;V (pin 7)''' goes only to the PDS slot (J13), so a bare board boots without it.
* '''−5&nbsp;V (pin 6)''' feeds the printer and modem line drivers (UE12, UD12) and the PDS slot, so a bare board boots without it too.
* '''+5&nbsp;V (pins 12 and 13)''' goes everywhere else. It is not optional.

With +5&nbsp;V alone you should see video output on pins 9, 10 and 11 on an oscilloscope, but the machine will not progress past horizontal lines because UB11 holds !RESET at around 2.5&nbsp;V. Add +12&nbsp;V to get further.<ref name="retrosixpin" />