Atari Falcon Troubleshooting Guide

Atari Falcon030

Fault-finding on the Atari Falcon030 follows Atari's Falcon030 Service Guide (C303062-001, 1 October 1992): its procedure for a dead unit, the Falcon030 diagnostic cartridge, and the symptom checklist in section 5.

Before you start

• Check the power supply first: +5 V and +12 V at the main board. Atari sets +5 V to 5.05 ± 0.1 V with a 4.0 A load and allows 5 % regulation on +5 V and 10 % on +12 V, with ripple and noise of 100 mV p-p each.
• Check that the monitor works and is the right type. The board reads the monochrome-detect line at power-up; if it does not see a low there, the VIDEL drives RGB instead of mono.
• Before blaming the hardware for a crash, check the disk and drive: Atari notes that errors loading files from disk can crash the system.

Start-up and bombs

After a reset the 68030 starts from the ROM, checks the cartridge port for a diagnostic or boot cartridge, initialises memory, the sound chip, the palettes, the MFP and the screen, then tries to boot from floppy and hard disk before loading the desktop from ROM. Exceptions without a handler draw bombs on the screen, one per exception number:

Number of bombs (Service Guide p. 62)

Bombs	Meaning
2	Bus error, asserted by COMBEL
3	Address error: word or long word access at an odd address
4	Illegal instruction
5	Divide by zero
6	CHK instruction without a handler
7	TRAPV instruction without a handler
8	Privilege violation
9	Trace
10	Line 1010 emulator
11	Line 1111 emulator

Dead unit

Atari's procedure when the unit is powered and correctly connected but shows no display (Section 3.3):

1. Connect a terminal to the RS-232 port at 9600 bps, 8 data bits, 1 stop bit, no parity (an STE running the VT52 emulator will do), with pins 2 and 3 crossed. Fit the diagnostic cartridge and switch on. If the cartridge's messages appear on the terminal, use the cartridge to find the fault.
2. Otherwise open the machine (see Atari Falcon General Maintenance). With a scope, check the 32 MHz clock to COMBEL; if it is missing, replace the oscillator. Check the 16 MHz clock to the 68030; if it is missing, replace COMBEL.
3. Check the 68030's HALT pin. It should be at TTL high. If it is low the CPU is halted by a bad reset circuit, a double bus error or a bad CPU: watch the BERR input at power-on for low pulses (COMBEL raising bus errors), check the cartridge ROM chip selects XROM3 and XROM4 (replace COMBEL if they are missing), and check the VIDEL display-enable output.
4. If the CPU is running, check the MFP serial output (pin 8) and the 1488 driver; RS-232 needs −12 V. Check the VIDEL's RGB or mono outputs; a picture that is present but unreadable points at the screen RAM.

A CPU too hot to touch for more than a second is, in Atari's words, a strong sign of a bad CPU.

Diagnostic cartridge

Atari's Falcon030 diagnostic cartridge runs on power-up with loop-back plugs on the ports. If the machine fails before the menu appears, the last message on screen points to the fault; a recoverable failure turns the screen red with a message and several rapid tones. The lowest 2 KB of RAM is tested first and failures are reported to the RS-232 terminal. Only the diagnostic menu (D) is meant for field use; the unattended and operator sections are for factory testing. If the clock battery has failed, the menu may show fewer choices.

The diagnostic menu offers RAM and DSP SRAM (R), OS ROMs (O), MIDI (M), SCC serial (S), timing (T), DSP port (D), floppy (F), printer, joystick and game ports (P), real-time clock (L), BLiTTER (G), SCSI (I) and expansion bus (X), plus audio, video, keyboard and IDE tests that need an operator. The real-time clock test reports C0 for no clock and C1 for an increment error. In the audio tests both outputs should give 4 V ± 0.2 V peak to peak.

Symptom checklist

Falcon030 symptom checklist (Service Guide Section 5)

Symptom	Probable cause (Atari)
Black screen	No power (check the LED), COMBEL, VIDEL; see the dead-unit procedure
White screen	VIDEL, COMBEL, SDMA, 68030; use the diagnostic cartridge with a terminal on the RS-232 port
Dots or bars on screen	Memory board, COMBEL, VIDEL
One colour missing	Video cable or connector, video DAC, VIDEL
Monochrome monitor will not sync but colour works	Monochrome detect not grounded; MFP GPIP bit 7; replace the MFP
Scrambled screen	COMBEL
Bad TV output	Modulator, phase-locked loop
Disk will not boot	Power supply, AJAX, SDMA, sound chip (PSG), IRQ lines shorted to ground; check the drive select light and motor, swap the drive
Disk will not format	AJAX, SDMA, drive
Crash after loading files	Disk, drive, AJAX, SDMA or COMBEL
Red screen: keyboard not responding	Keyboard, 6850, MFP
Red screen: MIDI errors	Opto-isolator, 6850, 74LS06 inverter
Red screen: SCC error	SCC, 1489 receiver, 1488 driver, PSG, ±12 V DC-to-DC inverting supply
Red screen: printer error	PSG, MFP
Shadow printing	Cables, terminator resistors, LS244 and LS245 drivers
Red screen: DMA error	SDMA, COMBEL, AJAX (loading the bus), 5380 SCSI controller
No DMA sound	+8 V regulator, ± supplies, DSP, CODEC, SDMA

In the parts list AJAX is the floppy controller, the MFP is an MC68901 (U31), the SCC a Z85C30 (U13), the RS-232 driver and receiver a 1488 (U5) and 1489A (U6, U14), the two ACIAs 68B50s (U24, U52), and the real-time clock a DS1287 (U64).

Clock battery

The real-time clock (U64) is a Dallas DS1287 with its own 3.6 V lithium cell and crystal; the cell cannot be changed separately. See Atari Falcon General Maintenance#Real-time clock battery.

Related pages

• Atari Falcon030
• Atari Falcon General Maintenance
• Atari Falcon Capacitor Replacement Guide