I have repaired nine motherboards of the Home Computer Texas Instruments TI-99/4A for a dear friend. Below the description of each repair.

Texas Instruments TI-99/4A Repair (1 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound … and then garbage screen.

Replaced parts:

• 1 x 1501392-27 ROM (U611)
• 2 x 4116 RAM (U102 / U105)
• 1 x 74LS245 OCTAL BUS TRANSCEIVER (U614)
• 1 x 74LS03 QUAD 2-INPUT NAND GATE (U506)

Texas Instruments TI-99/4A Repair (2 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x CD3227A ROM (U611)
• 1 x CD3226A ROM (U610)

Texas Instruments TI-99/4A Repair (3 of 9)

Defect:

• Garbage Screen.

Replaced parts:

• 4 x 4116 RAM (U105 / U106 / U108 / U109)

Texas Instruments TI-99/4A Repair (4 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x MCM 6810P RAM 128×8 (U609)

Texas Instruments TI-99/4A Repair (5 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x MCM 6810P RAM 128×8 (U608)
• 1 x 1501392-27 ROM (U611)
• 1 x 74LS138 1-OF-8 DECODER/DEMULTIPLEXER (U504)

Texas Instruments TI-99/4A Repair (6 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x CD3226A ROM (U610)
• 1 x 74LS138 1-OF-8 DECODER/DEMULTIPLEXER (U504)

Texas Instruments TI-99/4A Repair (7 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x TMS 9900-NL CPU (U600)

What happened to the other two motherboards ?

• The eighth motherboard was used for spare parts.
• The ninth motherboard has all components burned (Power Supply problem?)