Jump to content

Atari 1040STF 12 V Converter Whistle Repair

From RetroTechCollection
Atari 1040ST 12 V converter U62 (Atari Benelux bulletin 7)
The 12 V converter on the 1040ST main board as drawn in Atari Benelux's bulletin No. 7. The arrows mark the three parts the bulletin changes: R17, L4 and C28.

Some Atari 1040STF machines give out a faint whistle of about 12 kHz while they are running. Atari Benelux traced it to the small converter on the main board that produces about 12 V, and issued a fix that changes three parts around it.[1] The bulletin refers to the 1040, and the same original part values appear in Atari's 1040 STFM parts list of 1 May 1986.[2] See Atari 1040ST for the 1040 models.

The converter is U62, a TL497A switching regulator. It runs from +5 V through R17 and the inductor L4, and on the bulletin's drawing it produces +12 V at jumper JP2 and, through the charge pump C29, CR2 and CR3, −12 V at jumper JP3.[1] The 1040ST's internal power supply has no −12 V output, and Atari's manual notes that the RS-232 drivers need ±12 V.[3]

Symptoms

[edit | edit source]
  • A light, steady whistle at about 12 kHz from inside the case while the machine is on.[1]

A whistle is not the only noise these machines make. A hum at 50 or 100 Hz comes from the power supply's capacitor C1 and, according to Atari Benelux, is harmless; see Atari 1040STF Power Supply Repair. For other faults use the Atari ST Troubleshooting Guide.

Safety

[edit | edit source]

The work is on the main board, which runs at low voltage, but the power supply inside the same case is mains powered. Unplug the machine before opening it and keep clear of the supply's primary side; see Atari 1040STF Power Supply Repair#Safety.

Tools and parts

[edit | edit source]
Parts changed by Atari Benelux's bulletin No. 7
Position Fitted (bulletin) Fitted (1 May 1986 parts list) New value
R17 1 Ω 1 Ω, ¼ W carbon 5.1 Ω
L4 100 µH 100 µH, 10 %, axial 220 µH
C28 220 pF 100 pF, 50 V ceramic, axial 330 pF

Sources: bulletin No. 7[1] and Atari's parts list.[2] The bulletin and the parts list give different original values for C28; the new value is 330 pF in either case.

  • Soldering iron, solder and desoldering braid or pump.
  • A Phillips screwdriver and pliers for the shield's twist tabs.
  • A multimeter for the ±12 V checks afterwards.

Procedure

[edit | edit source]

Expose the main board

[edit | edit source]

Atari's 1040ST sequence:[3]

  1. Unplug the machine. Turn it upside down and remove the seven screws in the square holes and the three in the round holes, which hold the disk drive.
  2. Turn it upright, lift off the top case and unplug the keyboard harness at the right front corner.
  3. Lift the drive slightly and unplug its power harness and ribbon cable.
  4. Remove the power supply shield and supply, or leave the supply in place and remove the two screws that hold it to the case at its front corners through the holes in its shield.
  5. Remove the four screws at the front of the shield and board assembly, lift the assembly at the front and pull it forward out of the bottom case.
  6. Straighten the ten twist tabs, remove any copper tape and lift the upper shield straight up.

Change the three parts

[edit | edit source]
  1. Find U62, the TL497A, and the parts around it. Check them against the bulletin's drawing: R17 and L4 in series from +5 V, C28 beside the IC, R18 and R19 dividing the +12 V output, and the jumper wires JP2 and JP3 on the outputs.[1]
  2. Replace R17 with a 5.1 Ω resistor.[1]
  3. Replace L4 with a 220 µH inductor.[1]
  4. Replace C28 with a 330 pF capacitor.[1]

Reassemble

[edit | edit source]
  1. Refit the upper shield and twist the tabs, then put the board assembly back in the bottom case and refit the four front screws.[3]
  2. Refit the supply, the drive cables, the keyboard harness and the top case, with the three longer screws in the round holes.[3]
  3. Retest once the machine is back in its case. Atari recommends this after any reassembly, to catch shorts against the shield.[3]

Testing

[edit | edit source]
  1. Listen for the whistle with the machine running.[1]
  2. Measure +12 V at JP2 and −12 V at JP3 against ground with the machine on.[1]
  3. Test the RS-232 port, whose drivers need ±12 V. Atari's diagnostic cartridge reports RS-232 faults as S0 to SB; without the cartridge, connect a terminal or another ST running a VT52 emulator at 9600 bit/s, 8 data bits, 1 stop bit and no parity.[3]
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Atari (Benelux) B.V., Information Technique No. 7, "sifflement dans le 1040" (whistle in the 1040): the 12 kHz whistle, its source in the main-board converter, the drawing of U62 and its parts, and the new values for R17, L4 and C28. Hosted here: File:Atari Benelux technical bulletin 007 - 1040ST converter whistle.pdf.
  2. ↑ 2.0 2.1 Atari Corporation, 1040 STFM Parts List, 1 May 1986, pages 1–2, in the 520ST/1040ST Computer Field Service Manual (PDF pp. 59–60): R17 1 Ω, L4 100 µH, C28 100 pF, C26 150 pF, R18 1.2 kΩ, R19 12 kΩ and the twisted-pair jumper wires JP2 and JP3. Hosted here: File:Atari 520ST and 1040ST Computer Field Service Manual.pdf.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Atari Corporation, 520ST/1040ST Computer Field Service Manual, C026118-002 Rev B (3.6), January 1987. Section 1, the 1040ST supply's +5 V and +12 V outputs (p. 1.6, PDF p. 10); section 3, the RS-232 notes and the error codes S0–SB (PDF pp. 28–45); section 4, 1040ST disassembly (pp. 4.1–4.3, PDF pp. 46–48). Hosted here: File:Atari 520ST and 1040ST Computer Field Service Manual.pdf.


Retrieved from "https://retrotechwiki.com/index.php?title=Atari_1040STF_12_V_Converter_Whistle_Repair&oldid=30161"