Atari Jaguar Troubleshooting Guide

Jaguar main board 700026-001. The MC34163 regulator U38 is at the top right beside C150 and L29; the power jack and choke CH1 are at the top left

Fault-finding on the Atari Jaguar console, using Atari's schematic SCH. Jaguar Console (document 500162 Rev. 5.3, September 1993), the troubleshooting chart in Atari's user's guide, and repair reports from Retrostuff, JAMMArcade and James Jones. The Jaguar CD add-on is covered separately in the Atari Jaguar CD Troubleshooting Guide, and routine care in Atari Jaguar General Maintenance.

Before you start

Atari's user's guide gives these checks:

User's guide troubleshooting chart (p. 14, condensed)

Problem	Atari's remedy
No picture	Console and TV on; power cord and wall socket; RF switch box set to game; cartridge pushed firmly into the slot; TV on the Jaguar's channel; cables to the switch box
Screen solid red	Cartridge defective
Screen flickers or no colour	Antenna cables; TV fine tuning and colour controls; cartridge inserted properly
No game sound	TV volume; loose or disconnected cables
Power light does not come on	AC adaptor plugged in; power at the wall socket

• The Jaguar does not switch on without a cartridge in the slot. Atari's schematic routes the power switch through two cartridge connector pins, CART_OUT (B35) and CART_IN (B34), on the way to the regulator.
• Check the adaptor before anything else. Atari's adaptor, part number 500273, gives 9 V DC at 1.2 A with the centre pin negative. James Jones warns that reversed polarity "will fry your Jaguar's chips".

Will not switch on

The power circuit

Atari's schematic takes the adaptor input through the three-pin socket PSUCON and the choke CH1 to VIN, with C142 (10 µF) and a 20 V transient suppressor, SD1 (SA20A), across it. One pole of the power switch (SW1A) feeds the cartridge loop; the other (SW1B) sends 9 V to the audio regulator. The main +5 V rail comes from U38, an MC34163 switching regulator, with the 0.1 Ω current-sense resistor R169, the input capacitor C134 (330 µF), the Schottky diode D4 (1N5822), the 120 µH inductor L29 and the output capacitors C150 (2200 µF) and C174 (4.7 µF). There is no fuse between the socket and the regulators.

The power LED D3 is driven from the +5 V rail through R126 (150 Ω), so a dark LED with a cartridge in and the switch on means U38 is not delivering +5 V. The schematic notes that the LED is red on NTSC consoles and green on PAL ones.

U38 (MC34163)

U38 is the part most often destroyed by the wrong adaptor. Retrostuff plugged in the wrong supply by mistake, saw smoke at once, and found U38 (MC34163DW) burnt. Lifting the old chip pulled three pads with it, which had to be rebuilt with Kynar wire; the author notes that pad 7 must connect to the current-sense resistor and the via beside it. JAMMArcade's console, sold as dead, also had a blown regulator, which a new one cured.

1. Unplug the adaptor and remove the cartridge.
2. Remove the RF shield and look at U38 and the area around it for burn marks or a cracked package.
3. Check D4 and C150 at the same time, since they share the regulator's output.
4. To remove a damaged U38 without lifting pads, cut each leg free first, then desolder the legs one by one. Retrostuff's lifted pads came from removing the chip whole.

Test points

Power and supply test points (schematic 500162)

Point	What it is	Expected
VIN, at C142	Adaptor input after CH1	The adaptor voltage, 9 V nominal
VCC, at C150 or C174	Output of U38	+5 V
TP6	AUDIO_VCC, output of REG1 (LM78L05ACM)	+5 V
TP30	9 V to the A/V connector, through R83 (100 Ω)	About 9 V with the switch on

Rail names and test-point positions are from the schematic. The expected values follow the rail names on the drawing and the adaptor's rating; they are not measured figures.

No sound

Sound comes from Jerry through the TDA1545 DAC (U5) and the TDA1308T amplifier (U4), which run from AUDIO_VCC, a separate 5 V rail made by the LM78L05ACM regulator REG1 from the 9 V supply. Retrostuff's Jaguar had no sound after its U38 failure; C134 tested good, and replacing REG1 brought the sound back. The author links the fault to the absence of a fuse protecting the regulators.

1. Measure TP6. If AUDIO_VCC is missing or low while the 9 V side of REG1 (at C43) is present, replace REG1.
2. If AUDIO_VCC is good, check the output coupling capacitors C10 (right) and C34 (left) and the amplifier U4.
3. Before opening the console, try the TV volume and the cables, as the user's guide advises.

Picture faults

• A solid red screen means the cartridge has not been read; Atari's chart puts it down to a defective cartridge. Clean the cartridge contacts and reseat it.
• The video path runs from the RGB DAC U7 through the emitter followers Q2, Q3 and Q4 to the A/V connector, and through C14, C17 and C18 to the MC13077 encoder U3, which produces composite and S-video. The RF modulator takes composite video through C45. So a fault on RF alone points to the modulator, C45 or C11, while a fault on every output points back to U7 and the video supply (C7, C8).
• The encoder's PAL/NTSC input is tied through R19, marked "0R NTSC only", and a configuration resistor (R140, on input B4, "0=PAL 1=NTSC") tells the software which standard the console uses.

Related pages

• Atari Jaguar
• Atari Jaguar General Maintenance
• Atari Jaguar Capacitor Replacement Guide
• Atari Jaguar RGB Upgrade
• Atari Jaguar CD Troubleshooting Guide
• Atari Jaguar Documentation