Atari STE Troubleshooting Guide
Fault-finding for the Atari 520STE and Atari 1040STE. Both use the same main board and differ only in the RAM fitted: one bank of 512 KB on the 520STE, two on the 1040STE.[1] The STE combines the ST's GLUE and memory controller in one chip, the GSTMCU, and adds a new video Shifter with DMA stereo sound, the BLiTTER, SIMM memory and new game-controller ports for joysticks, paddles and a light gun.[1] For the earlier ST, STF and STFM see Atari ST Troubleshooting Guide. Routine care is on Atari STE General Maintenance and capacitors on Atari STE Capacitor Replacement Guide.
Warning: the internal power supply runs from mains voltage. Unplug the machine before removing the power supply shield.
Board and assemblies
[edit | edit source]Atari's parts list gives the bare board as C300779-001 and the schematic as drawing C300780-001. The US 1040STE with modulator is assembly CA400338-201, its main assembly (case, board, supply, keyboard and drive) CA400339-201, and its board assembly CA400340-111 with sub-assembly CA400329-101. The US supply is CA070059-003 (110 V).[2]
Main ICs
[edit | edit source]| Position | Part | Atari part number | Package |
|---|---|---|---|
| U100 | MC68000 CPU | C398061-001 | 68-pin PLCC, socketed |
| U101 | BLiTTER | C101643 | 68-pin PLCC, socketed |
| U102, U103 | TOS ROMs (TOS 1.62 on the US machine) | C301163-002, C301164-002 | 32-pin, socketed |
| U400 | GSTMCU | C300589-001 | 144-pin, surface-mounted |
| U401 | Shifter | C300588-001 | 84-pin PLCC in socket C100384-001 |
| U300 | DMA controller | C398739-001 | 40-pin |
| U301 | WD1772 floppy controller | C026028-002 | 28-pin |
| U202 | YM2149 sound generator | C025983 | 40-pin |
| U203 | MC68901 MFP | C025984 | 48-pin |
| U200, U201 | MC6850 ACIA (MIDI, keyboard) | C025985 | 24-pin |
| U204, U205 | TL497A switching regulator | C070447 | 14-pin |
| U206, U207 | MC1488 driver, 1489A receiver (RS-232) | C025986, C101739-001 | 14-pin |
| U208 | PC900 opto-coupler (MIDI in) | C025988 | 6-pin |
| U502, U503 | DAC0802 | C398057-001 | 16-pin |
| U505, U506 | MF4-100 filter | C398056-001 | 8-pin |
| U504, U507 | LF347 | C398055-001 | 14-pin |
| U508 | LMC1992 volume and tone control | C398058-001 | 28-pin |
| U513, U514 | LM556 (paddle inputs) | C025989 | 14-pin |
| U600–U603 | 30-pin SIMM sockets | C398063-001 |
Source: Atari's parts list,[2] with the role of the LM556s from the paddle test (section 3.17).[3] The retyped parts list prints most "C" prefixes as "0".
Clocks
[edit | edit source]| Position | Part | Frequency |
|---|---|---|
| U402 | Oscillator | 32.215905 MHz (NTSC); 32.084988 MHz on PAL machines |
| U303 | Oscillator | 8.010613 MHz |
| Y200 | Crystal (MFP) | 2.4576 MHz |
Sources: parts list and section 2.11.[2][1] The GSTMCU divides a 16 MHz clock down to 8 MHz, 4 MHz and 500 kHz.[1] The keyboard ACIA U201 should see 500 kHz ±50 kHz on pin 3.[3] The DMA sound sample rates are approximately 50, 25, 12.5 and 6.25 kHz.[1]
Power supply
[edit | edit source]The internal switching supply gives +5 V and +12 V only, through a 2 A fuse, and has over-current protection. Atari says to adjust it to 5.1 V, and that a blown fuse probably means a catastrophic failure such as a shorted primary, so find the fault before fitting a new fuse.[4]
| +5 V | +12 V | |
|---|---|---|
| Rating | 3 A | 0.9 A |
| Typical in the system | 1.75 A | 86 mA |
| Maximum, during disk access | 2.2 A | 90 mA |
Maximum input power is 33.5 W.[4]
The other supplies are made on the main board by two TL497A switching regulators. U204 makes the positive and negative supplies for the RS-232 drivers, normally ±12 V. U205 makes −5 V for the audio section, heavily filtered to keep switching noise out of the audio.[4] The audio section also has a +8 V regulator.[5] So:
- RS-232 errors with everything else working: Atari's checklist names the MFP, the 1489 receiver, the 1488 driver, the PSG and the ±12 V inverting supply (U204).[5]
- No DMA sound: Atari's checklist names the +8 V regulator, the ± supplies, the LMC1992, R542 and R543.[5]
Troubleshooting a dead unit
[edit | edit source]Atari's procedure, for a machine that is powered (LED lit) with a working monitor but no display:[3]
- Connect a terminal to the RS-232 port: pin 2 of the STE to pin 3 of the terminal and vice versa, pin 7 to pin 7, at 9600 baud, 8 data bits, 1 stop bit, no parity. Another STE running the VT52 emulator will do. Fit the diagnostic cartridge and switch on. If the cartridge's messages appear on the terminal, diagnose the machine from there.
- If nothing appears, expose the board and check the 8 MHz clock at the 68000 with an oscilloscope. Replace the oscillator if it is missing.
- Check the 68000's HALT pin. It should be at a TTL high. If it is low the CPU is halted, by a bad reset circuit, a double bus error or a bad CPU:
- reset circuit: look at the input of the two inverters on the HALT line;
- double bus error: watch BERR as the machine powers up. It should stay high. Low pulses mean a component is failing and the GSTMCU is generating bus errors; check the clocks into the GSTMCU, back to the Shifter and the master clock;
- otherwise the CPU cannot read ROM or a device is not answering, most likely the MFP or the DMA controller. The MFP should answer MFPCS with DTACK, and the DMA chip should answer FCS by asserting RDY. A bad CPU can only be found by elimination, but a CPU too hot to touch for more than a second is very likely bad.
- If the CPU is not halted, its address and data lines should be toggling; if not, replace the CPU. Check the MFP's serial output on pin 8 at power-up with the cartridge fitted and trace it through the 1488 driver, which needs ±12 V.
- Check the Shifter's outputs to the R, G and B summing resistors. If BLANK does not go high there is no picture. For monochrome, check the MONO output and the MONOMON input on MFP pin 29: if the CPU does not read it low at power-up, the Shifter puts out colour instead of monochrome.
- A Shifter signal with an unreadable picture points at the screen RAM. Use the cartridge with the terminal as the display.
Symptom checklist
[edit | edit source]| Symptom | Probable cause |
|---|---|
| Black screen | No power (check the LED), GSTMCU, Shifter |
| White screen | Shifter, GSTMCU, memory controller, DMA controller, 68000 |
| Dots or bars on screen | RAM, memory controller, Shifter |
| One colour missing | Video cable or connector, video summer, buffer, Shifter |
| Monochrome monitor will not sync, colour monitor works | Monochrome detect bit not grounded with the monitor connected; MFP GPIP bit 7; MFP |
| Scrambled screen | GSTMCU, memory controller |
| TV output bad | Modulator, phase-locked loop |
| Disk will not boot | Power supply, WD1772, DMA controller, PSG, drive, external ACSI buffer, external hard disk IRQ lines shorted to ground. Check that the drive select light comes on (if not, check the PSG outputs) and that the motor spins (if not, check the supply) |
| Disk will not format | WD1772, DMA controller, drive |
| Crash after loading files | Diskette, drive, WD1772, DMA, GSTMCU |
| Keyboard not responding | Keyboard, 6850, MFP |
| MIDI errors M0–M4 | Opto-isolator, 6850, 74LS06 inverter |
| RS-232 errors S0–SB | MFP, 1489, 1488, PSG, ±12 V inverting supply |
| Printer errors P0, P1 | PSG, MFP |
| Hard disk port errors D0–D2 | DMA controller, memory controller, WD1772 (loading the bus) |
| No DMA sound | +8 V regulator, ± supplies, LMC1992, R542, R543 |
Source: Atari's section 5.[5]
Diagnostic cartridge
[edit | edit source]At power-up the cartridge shows "Checking Exception Handling" and "testing MFP, GSTMCU timing, video", and the screen looks scrambled for a few seconds before the menu appears; that is normal. If an initial test fails the screen turns red (dark on a monochrome monitor) with a message. The lowest 2 KB of RAM is tested first and failures are reported on the RS-232 port, because a machine with bad RAM may have no readable screen. If the keyboard fails, the cartridge takes its commands from the terminal.[3]
| Code | Meaning |
|---|---|
| I1 | RAM data line stuck |
| I2 | RAM disturbance: a location is altered by a write to another |
| I3 | RAM addressing: the wrong location is addressed |
| I4 | MMU error: no DTACK after a RAM access |
| I5 | RAM sizing error: the uppermost address fails |
| I6 | A deliberate bus error crashed the machine |
| I7 | Bus error not detected: not asserted, or not reaching the CPU |
| Codes | Area | Notes |
|---|---|---|
| E6, E7, E8, E9, EA, EB | Exceptions | E6 autovector error (IPL0 grounded or a bad 68000); E7 spurious interrupt; EB bus error, with the address of the device being accessed |
| R0–R4 | RAM | R2 address line fault (RAM or memory controller); R3 address error at a 64 KB boundary; R4 video RAM test |
| K0–K2 | Keyboard | K1, no response: check that J202 pin 4 is at +5 V and U201 pin 3 has 500 kHz ±50 kHz, then replace the keyboard, U201, R210, R209 |
| M0–M4 | MIDI | Loopback test |
| P0, P1, J0–J8 | Printer, joystick and game-controller ports | J7 paddle, J8 light gun |
| S0–SB | RS-232 | S9–SB are the handshake loopbacks (DTR–RI, DTR–DCD, RTS–CTS) |
| D0–D3 | DMA | D3 DMA controller not responding |
| T0–T6 | Timing | T4 video address counter; T5 PSG and T6 WD1772 holding the data bus too long (replace the chip) |
| F0–FD | Floppy | F0 drive offline; FC side select; FD drive not ready |
| G1–GC | BLiTTER | A bus error during the BLiT test means replace the BLiTTER |
Source: Atari's quick reference, section 3.21.[3] For any BLiTTER error Atari's order is: check the BLiTTER's jumpers, replace the BLiTTER, then replace the 68000.[3]
Memory
[edit | edit source]The STE takes 30-pin SIMMs at U600–U603, two banks of two; each bank is a pair of 8-bit SIMMs making the 16-bit bus. Atari's rules are that every SIMM in the machine must be the same size (256 Kbit and 1 Mbit SIMMs cannot be mixed), all should have the same access time of no more than 150 ns, and 9-bit SIMMs can be used because the ninth bit is ignored.[1] A 520STE has one bank; the 1040STE's second bank is at 080000–0FFFFF. The two TOS ROMs are 128K × 8 parts at E00000–E3FFFF.[1]
For RAM faults, use the cartridge: I1–I5 at power-up and R0–R4 from the RAM test.[3] Reseat and clean the SIMMs and their sockets before replacing anything.
Bomb counts
[edit | edit source]TOS shows a row of bombs for an exception with no legitimate use. Atari's list:[6]
| Bombs | Meaning |
|---|---|
| 2 | Bus error, asserted by the GSTMCU |
| 3 | Address error: word or long-word access at an odd address |
| 4 | Illegal instruction |
| 5 | Divide by zero |
| 6, 7 | CHK and TRAPV instructions without a handler |
| 8 | Privilege violation |
| 9 | Trace |
| 10 | Line 1010 emulator (used by TOS for graphics) |
| 11 | Line 1111 emulator (reserved on the STE) |
| 24 | Spurious interrupt: bus error during interrupt processing |
Errors while loading files can also crash the machine. Atari's advice is to check the diskette and drive before repairing the computer.[6]
Disassembly
[edit | edit source]Atari's sequence:[7]
- Turn the machine upside down. Remove the six screws in the square holes, which hold the top case. To reach the board or remove the drive, also remove the three screws in the round holes, which hold the drive.
- Turn it upright, lift off the top case and unplug the keyboard harness at the right front corner.
- Drive: lift it slightly and unplug the power harness and ribbon cable.
- Power supply: remove one screw on the right of the supply shield and three screws between the rear EMI shield and the supply shield, straighten two twist tabs, lift the shield off from the rear, unplug the harness at the right front corner of the supply and remove the two screws at its front corners. The supply can stay in place with only the shield removed for testing.
- Main assembly: remove three screws at the front of the shield and board assembly, lift it at the front and pull it forward.
- Upper shield: straighten the twist tabs (usually four), remove any copper tape and lift the shield straight up.
Related pages
[edit | edit source]- Atari 520STE
- Atari 1040STE
- Atari STE General Maintenance
- Atari STE Capacitor Replacement Guide
- Atari ST Troubleshooting Guide
- Atari 520STE/1040STE Field Service Manual
- Floppy Drive Repair
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Atari Corporation, Atari STe 520/1040 Computer Field Service Manual, part number C302481-001 Rev A, August 1991, sections 2.0 to 2.12 (theory of operation), pp. 4–21. The hosted copy is a retyped edition by jer/eightbitter (May 2017) with redrawn schematics, not a scan of Atari's printing: File:520ste.pdf, described at Atari 520STE/1040STE Field Service Manual.
- ↑ 2.0 2.1 2.2 Atari Corporation, Atari STe 520/1040 Computer Field Service Manual, C302481-001 Rev A, section 7, "Parts List", pp. 52–55 (retyped 2017 edition, File:520ste.pdf).
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Atari Corporation, Atari STe 520/1040 Computer Field Service Manual, C302481-001 Rev A, section 3, "Testing", pp. 24–42 (retyped 2017 edition, File:520ste.pdf).
- ↑ 4.0 4.1 4.2 Atari Corporation, Atari STe 520/1040 Computer Field Service Manual, C302481-001 Rev A, sections 1.3, "Power Supply", and 1.4, "Negative Supplies", p. 3 (retyped 2017 edition, File:520ste.pdf).
- ↑ 5.0 5.1 5.2 5.3 Atari Corporation, Atari STe 520/1040 Computer Field Service Manual, C302481-001 Rev A, section 5, "Symptom Checklist", pp. 45–46 (retyped 2017 edition, File:520ste.pdf).
- ↑ 6.0 6.1 Atari Corporation, Atari STe 520/1040 Computer Field Service Manual, C302481-001 Rev A, section 2.14, "System Errors", p. 22 (retyped 2017 edition, File:520ste.pdf).
- ↑ Atari Corporation, Atari STe 520/1040 Computer Field Service Manual, C302481-001 Rev A, section 4.1, "STE Disassembly", pp. 43–44 (retyped 2017 edition, File:520ste.pdf).