Editing Macintosh SE/30 Troubleshooting (section)

== Preliminary Checks and Power Supply Basics ==

The SE/30 has three separate modules behind the logic board: a power supply (Apple 661-0370), an analogue board (661-0371) and a video board (982-0024). All three are shared with the Macintosh SE.<ref name="ssse30" /> Knowing which one you are accusing matters.

{{Warning|The CRT anode holds charge after power-off — discharge it before working on the analogue board, the video board or the CRT socket board. See [[CRT Discharge Procedure]]. The power supply's primary reservoir (620&nbsp;µF 400&nbsp;V, or a series pair of 330&nbsp;µF 200&nbsp;V depending on which unit is fitted) also stays charged; measure across it before touching the primary side.<ref name="c5se" />}}

Apple rates the machine at 120–240&nbsp;V AC, automatically configured, 48–62&nbsp;Hz, 75&nbsp;W maximum.<ref name="ssse30" /> Apple's Service Source publishes '''no rail tolerances and no voltage adjustment procedure''' for the SE/30 — there is no trimmer to turn. Its symptom chart sends a completely dark machine with a stopped fan to the power supply first, then the analogue board.<ref name="ssse30" />

{| class="wikitable"
|+
![[File:Analog connector front.png|none|thumb|274x274px|Macintosh SE/30 logic board analogue connector (front)]]
![[File:Analog connector back.png|none|thumb|311x311px|Macintosh SE/30 logic board analogue connector (back)]]
|}

If the unit is completely dead — no fan, no CRT glow, no chime — the analogue board is the usual culprit, and Larry Pina narrows it to specific components:<ref name="dms" />

* '''A dreadful hissing or sizzling noise with a dark screen''' — rectifier '''CR2''' shorted (0.00–0.01&nbsp;Ω). It is a GI854 barrel rectifier, R-51, 600&nbsp;V 3&nbsp;A; Pina fits an MR824 (R-51, 400&nbsp;V, 5&nbsp;A) instead to stop it recurring.
* '''Dead with no hissing noise''' — rectifier '''CR3''' shorted, same part. Then check the '''BU4060''' horizontal output transistor at '''Q2''' for burning, and after that the flyback at '''T2'''.

Also worth doing before anything else:

* Disconnect every external peripheral and any PDS card.
* Check the logic board for PRAM battery corrosion, and remove the cell. Apple's threshold for replacement is '''below 2.8&nbsp;V'''.<ref name="ssse30" />
* Replace all of the electrolytic capacitors on the logic board and check trace continuity around every one of them.

=== 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" />