Jump to content

Atari Jaguar Power Regulator Replacement

From RetroTechCollection
Atari Jaguar motherboard, U38 regulator area (C134, R169, D4, L29, C150)
The power corner of a 700026-001 board: the MC34163DW regulator U38 with R169 above it, C134 and C150 to its left, D4 to its right and L29 below (photo: Evan-Amos)

The Atari Jaguar makes its +5 V logic supply with a switching regulator, U38 (MC34163), and a separate 5 V supply for the sound circuits with a small linear regulator, REG1 (LM78L05ACM). Atari's schematic puts no fuse between the adaptor socket and either regulator.[1] Retrostuff plugged the wrong adaptor into a Jaguar, saw smoke at once and found U38 burnt; after U38 was replaced the console worked but had no sound, which a new REG1 cured.[2] JAMMArcade's console, bought as not powering up, also needed a new regulator.[3] The steps below test and replace both parts; fault-finding on the rest of the console is in the Atari Jaguar Troubleshooting Guide.

Symptoms

[edit | edit source]
  • No power LED with a cartridge in and the switch on. The LED D3 runs from the +5 V rail (VCC) through R126 (150 Ω), so a dark LED means that VCC is missing.[1]
  • Smoke or a burn mark at U38 after a wrong adaptor was used.[2]
  • Picture and game working, but no sound, after a power fault.[2]

The Jaguar does not switch on at all without a cartridge in the slot, so test with a cartridge fitted.[3]

Safety

[edit | edit source]
  • Unplug the adaptor before desoldering anything.
  • Check the adaptor before reconnecting it. Atari's adaptor (part 500273) gives 9 V DC at 1.2 A with the centre pin negative.[4] A wrong adaptor is what burnt U38 in Retrostuff's console, and the schematic shows no fuse on the input.[2][1] If the adaptor's plug needs replacing, see Atari Jaguar Power Adaptor Plug Replacement.

Tools and parts

[edit | edit source]
  • A multimeter, a fine-tipped soldering iron, flux and desoldering braid. See Recommended Tools.
  • Fine Kynar (wire-wrap) wire for any pads that lift. Retrostuff rebuilt three pads and a trace with it.[2]
  • For U38: an MC34163DW, the 16-pin wide SOIC version, as fitted on Atari's board.[1][5] onsemi's data sheet (revision 9, April 2025) lists MC34163DWR2G (tape and reel) and MC33163DWG and MC33163DWR2G as current, and MC34163DWG (rail) as discontinued. The MC33163 shares the data sheet and pin connections and is specified for −40 to +85 °C, against 0 to +70 °C for the MC34163.[6]
  • For REG1: an LM78L05ACM, the eight-pin SOIC version.[1] Texas Instruments lists LM78L05ACM/NOPB as active.[7]

Procedure

[edit | edit source]

1. Read the circuit

[edit | edit source]
Atari Jaguar schematic, power input, U38 and REG1
Atari's power section: VIN from PSUCON and CH1 at the left, U38 in the middle, VCC at the bottom right, and REG1 at the top right making AUDIO_VCC at TP6 (Atari schematic 500162 Rev. 5.3)

The adaptor enters at PSUCON and passes through the choke CH1 to VIN, which has C142 (10 µF), C141, C140 and the transient suppressor SD1 (SA20A) across it. VIN feeds U38 directly at pin 7 and through the 0.1 Ω, 1 W current-sense resistor R169 to pins 8 to 11, with C134 (330 µF) as the input capacitor. U38 switches through D4 (1N5822) and the 120 µH inductor L29 into C150 (2200 µF, "low Z"), C159, C174 (4.7 µF, "low Z") and C175 on VCC.[1]

The power switch has two halves. SW1A grounds CART_OUT, which runs through the cartridge connector and back as CART_IN to U38 pin 2; R166 (10 kΩ) pulls CART_IN up to VIN. SW1B passes VIN to the 9 V line that feeds REG1.[1] The data sheet says that the regulator's feedback comparator follows the higher of its two feedback inputs, pin 2 and pin 3, and that pin 3 has an internal divider set for 5.05 V.[6] On this circuit, then, CART_IN held high by R166 keeps U38 from switching, and the console only starts when a cartridge and the switch pull CART_IN to ground.[1][6]

U38 (MC34163) pins and their connections on the Jaguar
Pin Function (data sheet) Connection (Atari schematic)
1 Low voltage indicator output TP87
2 Voltage feedback 2 CART_IN, with R166 (10 kΩ) to VIN
3 Voltage feedback 1 VCC (+5 V output)
4, 5, 12, 13 Ground GND
6 Timing capacitor C168 (470 pF) to GND
7 VCC (supply) VIN, at C134 and one end of R169
8 Current sense Other end of R169
9 Driver collector Joined to pins 8, 10 and 11
10, 11 Switch collector Joined to pins 8 and 9
14, 15 Switch emitter D4 and L29
16 Bootstrap input C167 (22 nF) to the switch emitter

Pin functions are from onsemi's data sheet and connections from Atari's schematic.[6][1]

2. Measure before removing anything

[edit | edit source]
  1. Open the case and remove the steel RF shield over the main board.[8] On the 700026-001 board, U38 is in the top right corner with R169, C134, C150, D4 and L29 round it.[5]
  2. Fit a cartridge, connect a known-good adaptor and switch on.[3][4]
  3. Measure VIN at the positive end of C134. It should be the adaptor voltage, 9 V nominal.[1][4] If it is missing, the fault is before the regulator: the adaptor, its plug, PSUCON or CH1.[1]
  4. Measure U38 pin 2 (CART_IN). With the cartridge in and the switch on it should be pulled to ground. If it sits near VIN, the switch loop through SW1A and the cartridge connector is open, and U38 will stay off whatever its condition.[1][6]
  5. Measure VCC at the positive end of C150. U38's internal feedback is set for 5.05 V (4.9 to 5.2 V at 25 °C), so VCC should be close to 5 V.[6] If VIN is present, pin 2 is low and VCC is missing, U38 is the likely fault. The data sheet notes that an overloaded output trips U38's current limit, so with the adaptor unplugged also check that VCC is not shorted to ground before fitting a new chip.[6]
  6. Look at U38, R169, D4 and C150 for burn marks. D4 and C150 share U38's output.[1]

3. Replace U38

[edit | edit source]
Atari Jaguar U38 removed, showing the pads (retrostuff)
U38 removed. Retrostuff lifted three pads with the chip and rebuilt them with Kynar wire (photo: rosewood, retrostuff.org)
  1. Unplug the adaptor. Note which way round U38 is fitted, using the pin 1 mark on the chip, before taking it off.
  2. Desolder U38 without pulling on it. Retrostuff was not careful enough during removal and lifted three pads with the chip.[2] A reader who asked for help on the same post lifted one pad on his first attempt and the pad beside it on his second.[2]
  3. Clean the pads with flux and braid and inspect each one.
  4. Rebuild any lifted pad with Kynar wire to where its trace went. The author of the Retrostuff post told readers that pad 7 is the one that runs to the resistor R169 and to the via beside it, and that pad 3 is connected to the via on its right, so a wire can be soldered straight onto that via.[2] Use the pin table above to check where each pad should go.
  5. Fit the new MC34163DW the same way round as the old one and solder all sixteen pins.[6]
  6. Before reconnecting power, check the new joints for bridges, especially between pins tied to different nets in the table above.
Atari Jaguar U38 replaced, with the pad repair (retrostuff)
The new MC34163DW at U38, with the pads and the trace to R169 rebuilt in Kynar wire (photo: rosewood, retrostuff.org)

4. Check and replace REG1 if there is no sound

[edit | edit source]
Atari Jaguar motherboard, REG1 audio regulator and TP6
REG1 on a 700026-001 board, with R63 below it and TP6 to the right (photo: Evan-Amos)

REG1 makes AUDIO_VCC from the 9 V line after SW1B. AUDIO_VCC is brought out at TP6 and decoupled by C24 (2.2 µF) and C35 to AUDIO_GND.[1] On the 700026-001 board REG1 is to the right of centre in the lower half, near the TDA1308 amplifier U4.[5]

REG1 (LM78L05ACM, 8-pin SOIC) pins
Pin Function
1 Output (AUDIO_VCC, TP6)
2, 3, 6, 7 Ground
4, 5 No connection
8 Input (9 V from SW1B, at C43)

Pin functions are from the Texas Instruments data sheet; Atari's schematic draws REG1 with the same numbering.[7][1]

  1. With a cartridge in and the switch on, measure the 9 V line at the positive end of C43 or at REG1 pin 8.[1]
  2. Measure TP6 against AUDIO_GND (the negative end of C24). The data sheet's limits for the LM78L05 output are 4.75 to 5.25 V with 7 to 20 V at the input.[7]
  3. If the input is present and TP6 is missing or well outside that range, replace REG1. Retrostuff checked C134 first, found it good, and then replaced REG1, which brought the sound back.[2]
  4. Unplug the adaptor, desolder REG1, clean the pads and fit the new LM78L05ACM the same way round as the old one, checking its pin 1 mark.[7]
Atari Jaguar REG1 removed (retrostuff)
The REG1 pads after removal, between R63 and TP6 (photo: rosewood, retrostuff.org)

Testing

[edit | edit source]
  1. Fit a cartridge, connect the adaptor and switch on. The power LED should light, since it runs from VCC.[1]
  2. Measure VCC at C150: close to 5 V.[6]
  3. Measure TP6: 4.75 to 5.25 V.[7]
  4. Run a game with sound. Retrostuff confirmed its repair by playing Tempest 2000 with sound.[2]

Board revisions

[edit | edit source]

The part numbers, pin connections and references above are from schematic 500162 Rev. 5.3 and were checked against Evan-Amos's photograph of a 700026-001 board, which has an MC34163DW at U38 and REG1 in the same place.[1][5] Retrostuff's board, in the photographs above, has the same layout round U38. Check the silkscreen on other boards before working from these positions.

[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 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 Atari Corporation, SCH. Jaguar Console, document 500162 Rev. 5.3, 21 September 1993: power section (PSUCON, CH1, SD1, SW1A/SW1B, R166, U38 and its parts, REG1 and its parts, TP6, TP87) and power LED D3. Hosted here as File:Atari Jaguar Console Schematic 500162 Rev 5.3.pdf.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 rosewood, "Atari Jaguar Power/Sound Fix and Rotary Controller", retrostuff.org, 21 August 2016, with the author's replies to a reader in the comments (24 and 29 August 2018). Personal repair log.
  3. ↑ 3.0 3.1 3.2 Porchy, "Atari Jaguar repair log", JAMMArcade.net, 14 December 2014. Personal repair log.
  4. ↑ 4.0 4.1 4.2 Evan-Amos, photograph of the Atari Jaguar/Jaguar CD adaptor model PP-912 and its label (Atari P/N 500273, output 9 V DC 1.2 A, centre negative), 20 June 2014. Hosted here as File:Atari Jaguar power supply (PP-912).jpg.
  5. ↑ 5.0 5.1 5.2 5.3 Evan-Amos, photograph of an Atari Jaguar main board, assembly 700026 (label 700026-001), 21 June 2014. Hosted here as File:Atari Jaguar motherboard (700026-001).jpg; crops as File:Atari Jaguar motherboard, U38 regulator area (C134, R169, D4, L29, C150).jpg and File:Atari Jaguar motherboard, REG1 audio regulator and TP6.jpg.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 onsemi, MC34163, MC33163 Switching Regulators – Step-Up/Down, Inverting, 3.4 A, data sheet MC34163/D, revision 9, April 2025: pin connections (p. 1), maximum ratings and feedback comparator thresholds (pp. 2–3), operating description (p. 8), ordering information (p. 15).
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Texas Instruments, LM78L 100mA Fixed Output Linear Regulator, SNVS754O, revised August 2026: pin configuration and functions (p. 3), LM78L05 electrical characteristics (p. 5) and the package option addendum.
  8. ↑ Evan-Amos, photograph of a Jaguar with the top case removed and the RF shield in place, 19 June 2014. Hosted here as File:Atari Jaguar with RF shield in place.jpg.


Retrieved from "https://retrotechwiki.com/index.php?title=Atari_Jaguar_Power_Regulator_Replacement&oldid=30688"