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Atari TT030 Power Supply Repair

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Phihong PSM-5341 schematic (TT and Mega STE copy)
Phihong's schematic of the PSM-5341, the TT030's power supply, from a copy marked "TT/MSTE". Mains enters at the left; the four outputs and the Power Good line leave at the right.

The Atari TT030 has an internal switching power supply rated by Atari at 64 W from 100–240 V AC, giving +5 V at 7 A, +12 V at 2 A, −5 V at 0.4 A and −12 V at 0.3 A. Atari's parts list gives it as a Phihong PSM 5341; an engineering change of 21 November 1990 (ECO 3005) changed the part number from C301379-001 to C302074-001.[1] The same Phihong model is used in the Atari Mega STE.[2]

The supply's own documents, Phihong's specification for part C301379-001 and its schematic, are hosted on the wiki. The fault-finding, adjustment and recapping of the supply itself are on Atari Mega STE Power Supply Repair, because the board is the same. What differs in the TT030 is the supply's removal and refitting, its connection to the main board, and a factory rework that protects the board from the supply's mounting foot.[3]

Symptoms

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  • The power LED at the front left corner does not light. Atari's first step is to check the supply voltages, adjust them if necessary, and replace the supply if it is defective; if the LED still does not light, check the LED itself.[1]
  • Black screen: Atari's checklist starts with no power.[1]
  • A disk that will not boot: Atari's checklist lists the supply first.[1]
  • Power problems after the supply has been taken out and refitted: the insulation over F61 and L601 (below).[4]

See also the Atari TT Troubleshooting Guide.

Safety

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Warning: the supply works from the mains, and its 400 V reservoir capacitors hold a dangerous charge after the machine is unplugged. Phihong's schematic shows C6 (120 µF 400 V) and C7 (10 µF 400 V) on the primary side.[3] Measure across them before touching the board, and never run the supply without a load; Phihong specifies a minimum of 2 A on +5 V and 0.2 A on +12 V.[3]

Tools and parts

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  • A screwdriver for the ten bottom-cover screws, and a slotted screwdriver for the accessory cover's retaining screw.[1]
  • A multimeter; dummy loads for a bench test, as on Atari Mega STE Power Supply Repair#Bench test.
  • Insulating tubing and tape for the F61 and L601 rework.[4]
Supply to main board: Phihong's wire list and the TT030 connector J100
Pin Wire colour Signal
1 Orange Power Good
2 – Phihong: open. Atari's schematic: +5 V
3 Yellow +12 V
4 Blue −12 V
5, 6, 7, 8 Black Ground
9 White −5 V
10, 11, 12 Red +5 V

Sources: Phihong's wire list[3] and Atari's TT030 schematic, which shows J100 with the same rails.[5]

Procedure

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Remove the top cover

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Atari's sequence:[1]

  1. Switch off and disconnect all cables from the sides and back, including the keyboard, mains lead and any external drive.
  2. Turn the computer over and rest it on its top.
  3. Remove the ten screws in the square holes in the bottom cover.
  4. Loosen the retaining screw of the accessory cover with a slotted screwdriver.
  5. Holding the top cover, base and accessory cover together, turn the unit back over onto its base.
  6. Lift the front of the accessory cover and remove it. If a hard disk is fitted, stand it on its side on the top cover and disconnect its power and interface cables.
  7. Lift the top cover off and stand it on its back behind the base, taking care of the floppy drive cables and the power LED cable.
  8. Disconnect the power, interface and LED cables from the floppy drive and set the top cover aside.

Remove the supply

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  1. Disconnect the supply's cables from the floppy drive, and from the hard disk if one is fitted.[1]
  2. Unplug the supply's main connector from J100 on the main board.[5]
  3. Remove the two screws holding the supply and lift it out.[1]

Test and repair the supply

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Test the supply on the bench into dummy loads, and repair or recap it, as described on Atari Mega STE Power Supply Repair: the bench test, the primary-side checks along Phihong's schematic, the +5 V alignment with R23 and R24, and the optocoupler.[3] The capacitor list for the PSM-5341 is on the Atari Mega STE Capacitor Replacement Guide.

Check the F61 and L601 rework

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  1. Find fuse F61 and ferrite bead L601 on the main board, near the supply's mounting foot.[4]
  2. Check that both are covered with insulating tubing and then insulating tape, as Atari's rework for ECO 1323 requires. Replace any insulation that has come away.[4]
  3. F61 (5.0 A) and L601 are in the supply to the cartridge port J601; if the port has stopped working, check F61.[6]

Refit the supply

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Atari's sequence:[1]

  1. Put the supply back in place and refit its two screws.
  2. Reconnect J100, then the supply cables to the floppy drive and, if fitted, the hard disk.
  3. Refit the top cover: reconnect the floppy drive's power, interface and LED cables, set the cover on the base, refit the accessory cover (and hard disk), turn the unit over and refit the ten screws, then tighten the accessory cover's retaining screw.

Testing

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  1. Switch on and check that the power LED lights.[1]
  2. Measure Power Good and each rail at J100 with the machine running.[5]
  3. Compare them with Phihong's limits: +5 V within +5 % and −4 %, +12 V and −5 V within 5 %, −12 V within 10 %.[3]
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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Atari Corporation, Atari TT030 Computer Field Service Manual, C302483-001, August 1991. Section 1.4.1, power supply rating (printed p. 3, PDF p. 10); section 3, troubleshooting a dead unit, the power LED and the supply (PDF p. 38); section 4, disassembly and reassembly: top cover, power supply and main board removal (printed pp. 67–70, PDF pp. 74–77); section 5, symptom checklist (PDF pp. 79–80); section 7, parts list, ECO 3005 and the power supply C302074-001, Phihong PSM 5341 (PDF pp. 99–101). Hosted here: Atari TT030 Computer Field Service Manual (PDF).
  2. ↑ exxos (Chris Swinson), "The LaST Upgrade, part 6: Atari PSU repair", exxosforum.co.uk, section "MSTE PSU Phihong PSM-5341": the supply and its schematic, labelled for the Mega STE and TT030.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Phihong Enterprise Co., Ltd., Switching Power Supply Specification, model PSM-5341, drawing PES10442, part number C301379-001, revision A, 20 September 1990, and schematic PES-30391 revision 01 (copy marked "TT/MSTE"). Hosted here: File:Phihong PSM-5341 Power Supply Specification and Schematic.pdf.
  4. ↑ 4.0 4.1 4.2 4.3 Atari Microsystems Corporation, Assy. Drawing, TT030 32 MHz, drawing CA400961, 16 May 1991, in the Atari TT030 Computer Field Service Manual, section 8 (PDF p. 112): the rework for ECO 1323 covering fuse F61 and ferrite bead L601 with insulating tubing and tape so that they cannot short to the power supply's mounting foot. Hosted here: File:Atari TT030 Computer Field Service Manual.pdf.
  5. ↑ 5.0 5.1 5.2 Atari Corporation, TT030/32 schematic, drawing C301762-001, sheet 1: power connector J100 and its decoupling. Hosted here: Atari TT030 Schematic (PDF).
  6. ↑ Atari Corporation, TT030/32 schematic, drawing C301762-001, sheet 6, in the Atari TT030 Computer Field Service Manual, section 8 (PDF p. 119): cartridge port J601, fuse F61 5.0 A, ferrite bead L601. Hosted here: File:Atari TT030 Computer Field Service Manual.pdf.


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