Macintosh SE/30 Troubleshooting

This guide provides solutions to common faults experienced in the Macintosh SE/30. From power issues to Simasimac patterns and SCSI failures, these diagnostics will help identify, isolate, and resolve problems.

Preliminary Checks and Power Supply Basics

Begin by verifying the analog board delivers proper voltages:

+5V rail: 4.90V – 5.10V
+12V rail: Confirmed at floppy or hard drive connectors


Macintosh SE/30 Logic Board Analog Connector (Front)	Macintosh SE/30 Logic Board Analog Connector (Back)

If the unit is completely dead (no fan, CRT glow, or chime), inspect

Fuses
Rectifiers CR2 and CR3
Transistor Q2
Resistor R22

Also:

Disconnect external peripherals and cards
Check logic board for PRAM battery corrosion
Replace all electrolytic capacitors on the logic board

Power Rails

Attempting to power up the motherboard on its own with just a bench power supply and minimum rails, using an oscilloscope to see video output.

12V Rail (J12 pin 14) goes to external and internal drives, external PDS connector and sound, so will boot without 12V to some degree, however the sound chip UB11 will hold the system in reset so you will only get to horizontal lines/simasimac screen at most.

J6 (External 3.5" Floppy Drive)
J8 (Internal Floppy Drive)
J13 (PDS video/expansion slot)
UB10/UB11/UA9 (Sound)

-12V Rail (J12 pin 7) goes to the PDS slot only, so should definitely boot without it.

J13 (PDS video/expansion slot)

-5V Rail (J12 pin 6) goes to the line drivers for the printer and modem, and the PDS port, so again should at least boot without it.

UE12 / UD12 (Line drivers for printer and modem)
J13 (PDS video/expansion slot)

This leaves the 5V rail (J12 pin 12/13) which goes everywhere else to loads of logic. This is absolutely needed.

Based on that, the system should at least boot with some video output on J12 (pins 9/10/11) you can observe with an oscilloscope with just the motherboard and 5V rail powered. However, due to UB11 sound chip not having power it will hold the !RESET line at 2.5V getting to horizontal lines/simasimac screen at most.

To get to a further boot, you need to also apply the 12V rail.

"Simasimac" – Horizontal Stripe Pattern

The infamous "Simasimac" pattern shows horizontal black-and-white lines with no startup chime. Causes include:

Leaking capacitors disrupting the reset circuit
Corroded traces or vias near RAM/ROM

Solutions:

Clean and reseat ROM and RAM SIMMs
Replace PRAM battery if < 3V
Check for reset pulse at CPU
Test for 16 MHz clock at CPU
Inspect Apple Sound Chip (ASC) at UB11 and filter RP2
Use multimeter or oscilloscope to confirm continuity

Chimes of Death and Sad Mac Codes

The Chimes of Death signify early boot failure—commonly RAM or ROM faults.

Checklist:

Use 4 matched SIMMs per bank
Larger-capacity SIMMs go in Bank A
Clean/reseat ROM SIMM
Check address/data continuity near capacitors
Replace 74F258 multiplexers or RAM if needed
Check VIA chips for overheating or corrosion

See: Sad Mac Error Codes for detailed interpretation.

Video Display Issues

No Video but Chime Present

Verify brightness knob
Confirm CRT glow
Check UE8 (video multiplexer)
Probe video/sync signals at P1 connector

Vertical "Jailbar" Stripes

Indicates incorrect RAM configuration
Use identical SIMMs per bank (larger ones in Bank A)

Checkerboard Pattern

Typically a ROM failure
Clean/reseat the ROM SIMM
Confirm compatibility (use SE/30 or IIsi ROMs only)

Disk Drive and SCSI Issues

Frozen Mouse on Gray Screen

Possible failure of SCSI controller (NCR 53C80)
Disconnect all internal/external SCSI devices
Inspect and replace termination resistors

Floppy Drive Issues

Dirty mechanism
Faulty SWIM controller
Cold solder joints on VIA or SWIM ICs

For more, see:

Audio and ADB Issues

No Sound

Test audio at the headphone jack
Inspect ASC (Apple Sound Chip)
Inspect analog board audio amplifier

ADB Malfunction

Blown fuse F1
Failed ADB microcontroller (Egret)
VIA chip solder cracks or corrosion

Reset and Clock Problems

Random resets: Check power rail stability
No time retention: Dead PRAM battery or failed 32.768 kHz crystal
Check surrounding electrolyte residue near Egret or VIA chips

It is best to check the crystals are operating as nothing on the board will generally work without them.

Using an oscilloscope check the crystal closest to the ROM (front right) which should be 32.77kHz sine wave with the top pad being a little more square. It should be around 3V to 4V peak-to-peak.

!Reset Line

Several chips can be held in reset or control the reset of other chips. Although the video output circuit works regardless of the state of the reset line (so you can see the horizontal lines/simasimac) the system won't do anything useful until out of reset.

The reset line connects to:

In/Out 68030 (UK8) !RESET
VIA1 (UK12) pin 37
VIA2 (UK11) pin 37
Apple Desktop Bus ADB Chip (UL11) pin 4 (for keyboard/mouse)
Super Woz Integrated Machine SWIM (UJ11) pin 25 (for floppy drive)
53C80 SCSI Controller (UI12) pin 7 (for HDD)
ASC stereo sound chip (UE10) pin 40
Sony Sound Chip (UB11) pin 5

Any or all of these chips can cause the !RESET To not go high even if they are inputs as if they go faulty it could pull the pin lower.

Minimal Boot Requirements

If you have a major issue like no bus activity, no boot sound, or even no AV out, it is best to start with the absolute minimal boot, and look for the address bus toggling constantly on power up, or the initial boot audio chime.

Critical ICs

The initial startup is done by the Glue Logic chip UI8. I have not fully reverse-engineered its boot-up yet but have found all required chips.

The following ICs are critical for the boot operation of the system to get to the out of reset address toggling state.

68030 CPU (UK8)
Glue Logic (UI8)
PAL for RAM Signals (UH7)
PAL for 68k/Video Signals (UI6)
Resistor Packs for Pull-Ups (RP7 / RP9)
Sound IC (UE10)
ROM (J14) if you want to hear boot sounds, if not oscilloscope for address bus activity

To boot from only 5V you want to remove the sound chips too and with up the headphone port so you can still hear audio from the headphones:

Remove UB10 / UB11
Jumper between UB11 pins 8 and 9 to short together analog and digital grounds (audio will be a little noisy). This also makes the S2 NMI button work again as once UB11 is removed the analog and digital grounds are separated and the reset button uses the disconnected ground. NOTE: S1 normal reset button won't work with UB10 removed as it is responsible for sensing that button and pulling reset low. So use S2 or disconnect power to reset.

Non-Essential ICs

You can remove all non-essential chips in case them failing pulls voltage rails or lines bad if you are still struggling to diagnose:

UD1
UK4 (RTC)
UD12 / UE12 / UG12 / UI12
UK12 / UJ11 / UK11 / UL11
UI5 (FPU)
All RAM (Because if it successfully checks RAM but UG12/UI12 or UJ11 fail or are missing you won't hear any beep and get horizontal lines)
UK6 (Video IC)
UE6 / UG6 / UE7 / UG7 (PALs)
UC6 / UC7 (Video RAM)
UA8 / UB8 / UC8 / UD8 / UE8 / UF8 / UG8
UI2 / UJ2 / UI3 / UJ3 / UJ4 / UI4 / UJ6 (Logic)
RP1 / RP4 / RP5 / RP6 / RP8 (Resistor packs)

Expected Boot

With just the critical ICs installed, if you have also removed the sound chip and bridged the audio jack (otherwise if not you will need 12V power applied also) you should expect to hear a sad mac boot sound when power is applied.

If you have no ROM, instead you can probe the lower address pins of the ROM socket and they should be constantly pulsing.

If you do not see this, perhaps check all the following chips happy to come out of reset:

In/Out 68030 (UK8) !RESET
VIA1 (UK12) pin 37
VIA2 (UK11) pin 37
Apple Desktop Bus ADB Chip (UL11) pin 4 (for keyboard/mouse)
Super Woz Integrated Machine SWIM (UJ11) pin 25 (for floppy drive)
53C80 SCSI Controller (UI12) pin 7 (for HDD)
ASC stereo sound chip (UE10) pin 40
Sony Sound Chip (UB11) pin 5

Initial Boot Sequence

After the Glue Logic chip brings all required pins on the 68k to their initial state the 68k should attempt to walk the bus and you will see constant address pins toggling as it loops over and over attempting a load.

The 68030 has a bi-directional reset signal meaning it can both set the reset signal, and be reset by external sources. The minimum required to see some activity on the 68k:

VCC must be 5V
Valid CLK pulse
!RESET must be high (to come out of reset)
!HALT must be high (to not be halted)

!BERR

When the 68030 attempts to access memory or an I/O device, it uses the address and data buses to communicate with the external chips and hardware.

If something goes wrong during this communication, such as a memory access error, a parity error, or a failure to receive a data acknowledge signal, a "bus error" is generated.

This !BERR is then sent low by some other device (the one the 68030 attempted to read/write invalid address data to) and so it halts its execution and goes into an error handling state.

If you see !BERR toggling low it is a sign something isn't happy with the data/address bus and something is invalid.

On the Macintosh SE/30 the following chips connect to !BERR:

68030 CPU (UK8)
PAL1644B (UI6)
Glue Chip (UI8)
PDS Header (J13)

It is pulled up to 5V through the resistor pack RP7 so make sure that is connected and pulled high otherwise it would be constantly low.

This means that as the !BERR is an input into the 68030, and the PDS header is generally empty for initial boot attempts, the Glue chip or the PAL must be the ones driving the !BERR low.

Brief Analog Board Troubleshooting

Vertical line only: Horizontal deflection fault – reflow P1 connector and replace C15
Horizontal line only: Vertical deflection fault – reflow P1 and replace TDA1170A
Wavy or distorted video: Failing flyback transformer
PSU clicking repeatedly: Shorted logic board or failed CR2, CR3, Q2, or R22

Related Pages