Texas Instruments TI-99/4A Repair #1

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS9900NL CPU (U600)

Texas Instruments TI-99/4A Repair #2

Defect:

• Wave/Raster Lines.
• Garbage on Boot Screen.

Replaced parts:

• 1 x Inductor 2 -> 4.5 μH (L100)
• 2 x TMS4116-15 RAM

Texas Instruments TI-99/4A Repair #3

Defect:

• Garbage on Boot Screen.

Replaced parts:

• 1 x MOSTEK MK4116N RAM

5 x TI-99/4A (PAL) motherboards with various defects repaired

Defect:

• TI-99/4a #1: The metal shield that protects the pcb is loose and some parts create short circuits on the pcb.
• TI-99/4a #2: TMS 9918 (U100) VDP inserted in the wrong way (:/), incredibly it did not burn.
• TI-99/4a #3: TMS 9900 (U600) Dead CPU.
• TI-99/4a #4: TMS 9900 (U600) Dead CPU.
• TI-99/4a #5: Apparently working. (Notes: left ON for over 4 hours did not present any problems)

Gallery of the repair:

Texas Instruments TI-99/4A Repair.

Defect:

• Garbage boot screen.

Replaced parts:

• 2 x TMS4116-15 RAM (U102 / U105)

Gallery of the repair:

Texas Instruments TI-99/4A Repair (1 of 6)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS 4732/2532 ROM (U610)

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 Texas Instruments TI-99/4A Repair (2 of 6)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x MCM 6810P (128 x 8-Bit Random-Access Memory TTL/DTL) (U608)

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Texas Instruments TI-99/4A Repair (3 of 6)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x 74LS138 (U504)
• 1 x 74LS138 (U505)

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

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS 9900NL CPU (U600)

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Texas Instruments TI-99/4A Repair (5 of 6)

Defect:

• Garbage Boot Screen.

Replaced parts:

• 1 x TMS4116-15 RAM (U106)

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

Defect:

• Various problems with audio playback.

Replaced parts:

• 1 x SN76494N – Digital Complex Sound Generator (U511)

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Texas Instruments TI-99 Power Supply Repair.

Defect:

• Missing 16v (AC)

Repair:

• Replaced the Thermal Fuse with one of 125° 2A (see photo).

Gallery of the repair:

Texas Instruments TI-99/4a Repair.

Defects:

• Black Screen and deafening sound in background.
• Garbage Boot Screen.

Replaced parts:

• 1 x SIGNETICS C2E011 ROM (U610)
• 1 x TMS4116-15 RAM (U106)

Gallery of the repair:

Texas Instruments TI-99/4a Argentine (Spanish) Version Repair.

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS 9900NL CPU (U600)
• 1 x Burned Resistor (15 Ohm)

Note: This motherboard has already been repaired by someone at least once.

Gallery of the repair:

Texas Instruments TI-99/4A Repair (1 of 2)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS 4732/2532 ROM (U611)

Gallery of the repair:

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

Defect:

• Garbage Screen.

Replaced parts:

• 1 x TMS4116-20 RAM (U103).

Gallery of the repair:

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Download: TI99 Technical Manual (751)

Texas Instruments TI-99/4A Repair.

Defect:

• Cartridges port doesn’t work.

Fix:

• Cleaning the cartridge connector (computer side) with one pin oxided.

Gallery of the repair:

Texas Instruments TI-99/4A Repair (1 of 3)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS9900NL CPU (U600)

Personal note that is good for all repairs:

Repairs are done with experience and skill, if there is skill does not mean that there is also the experience.

Repairing any electronic things by desoldering everything to find the bad components is not an index of experience but only ability.

Gallery of the repair:

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Texas Instruments TI-99/4A Repair (2 of 3)

Defect:

• Garbage Screen.

Replaced parts:

• 1 x TMS4116-15 RAM

Gallery of the repair:

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

Defect:

• Man lacks his legs and miss a piece of rope in the pitfall game demo.

Replaced parts:

• 1 x TMS9929TML VDC (Video Display Controller)

Gallery of the repair:

PPI Super Sketch for Texas Instruments TI-99 Repair.

Defect:

• The cartridge is not recognized by the TI-99/4A.

Repair:

• Replaced 1 x 74LS139 (U1)
• Replaced 1 x 74LS30 (U2)

Note:

The repair of the Super Sketch cartridge was quite simple, in the first time i thought a problem of the ROM but instead the failure was the two IC U1 and U2, which should do the work of the Bank Switching.

To remove the two IC i have preferred to cut the pins and then remove each pin because i know very well this type of PCB and also lowering the temperature there is a risk that the pitches come off.

Gallery of the repair:

Texas Instruments TI-99/4A Repair (Wave/Raster Lines)

Defect:

• Wave/Raster Lines (see photo).

Replaced parts:

• 1 x Variable Inductor 2 -> 4.5 μH (L100).

Gallery of the repair:

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

Defect:

• Wave/Raster Lines.

Replaced parts:

• 1 x Variable Inductor 2 -> 4.5 μH (L100).

Gallery of repair:

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

I should point out that someone has already tried to repair, without success.

Defects:

• Black Screen (no raster, no sync) short circuit between 12v and 5v . . . and then . . .
• Wave/Raster Lines.
• Blue Screen with tiny Vertical lines and deafening sound.
• Garbage Screen.

Short Circuit Note:

• The short circuit was due to a malfunction of the IC: TIM9904ANL (U601)

Replaced parts:

• 1 x Variable Inductor 2 -> 4.5 μH (L100).
• 1 x TIM9904ANL (U601)
• 2 x MCM 6810P RAM 128×8 (U608 – U609)
• 1 x 74LS245 (U614)
• 1 x TMS9929 (U100)

Gallery of the repair:

Repairing Radio Shack TRS-80 Model 1 ..for the third time

Defect:

• SHIFT keyboard switch broken.
• Garbage Screen on boot (already repaired).
• Flat cable of the Keyboard broken (already repaired)

Repair:

• Replaced the keyboard switch with a new one taken from a keyboard (the good one) of the Texas Instruments TI-99/4A that helps me many times.
• Replaced a 2102 Video SRAM.
• Rebuilt the keyboard flat cable.

Gallery of he repair:

We begin to explain what is this PHA-2037. This interface/Converter for the Home Computer Texas Instruments TI-99/4a is used to convert the video signals from Component (Y/Pb/Pr) to RGB (Scart Standard).

The defect of the PHA-2037 that i have received for repairing is to display images without the “BLUE” color in this case of the Video Component “Pb”.

The problem was in one of the three LM 318 (Op Amp). Just replaced, the PHA-2037 has begun to work properly.

PS: How you can see from a photo a pin of a transistor has not been cut. Maybe it was better to do it. :D

Gallery of the repair: