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Atari Technical Bulletin
Number: MSTE-0002
Date: September 13, 1991
Page 1 of 2


Product(s) Affected:		MEGA STE, (STE)
Model:					All models
Type of ATB:				As Needed
ECO #: 					N/A

Reason for ATB:

Audio distortion caused by shifter I.C. not installed correctly.


Notes:

Description			Part number	Location

Shifter Revision B		C300588-001	U502
Shifter Revision D		C301712-001	U502
74LS02 IC				C101611-002	U699

Symptoms of Problem:

Audio distortion during DMA sound.


Tests to Determine if Problem Exists:

Check stereo sound port with oscilloscope using diagnostic cartridge to see if waveform is distorted.  (SEE AUDIO TEST IN FIELD SERVICE MANUAL)

Solution:

The revision B shifter (C300588-001) requires a 74LS02 at location U699. If the revision B is replaced with the revision D shifter (C301712-001), then U699 must be disabled. (See rework instructions)


Shifter version				Solution

C300588-001 Rev B		74LS02 enabled
C301712-001 Rev D		74LS02 disabled

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Atari Technical Bulletin
Number: MSTE-0002
Date: September 13, 1991
Page 2 of 2


Rework required to disable 74LS02 on MEGA STE (U699)

Cut pins 1 and 13 of the 74LS02 at U699 (disconnect output)

Add a jumper from pin 2 of the 74LS02 at U699 to pin 1 of U699 on the PCB (do not connect the jumper to the cut pin on the 74LS02)

Add a jumper from pin 12 of the 74LS02 at U699 to pin 13 of U699 on the PCB (do not connect the jumper to the cut pin on the 74LS02)