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Retro_Game_Lover96

RGB Mod Explanation

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13 hours ago, Retro_Game_Lover96 said:

Ooh-de-lally! It works like a charm after I added the 560 ohm resistors, so I finally got color via TMS RGB!!! :D

I guess that unlocks the procedure for adapting a TI-99.  Though it sounds like different revisions will have different levels of needed changes.  But @Falonn should now be able to add some docs to his page on this.

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18 hours ago, Retro_Game_Lover96 said:

Ooh-de-lally! It works like a charm after I added the 560 ohm resistors, so I finally got color via TMS RGB!!! :D

 

F52E619D-8F29-48C5-9F0A-E7056334B47A.jpeg

Can you make a "How to...!" on this?

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How to add RGB on TI99/4A?

Requirement tools/parts:

A working TI99/4A Computer

TMS-RGB Mod Board (Assembled)

8 Pin Mini Din Female connector

8 Pin Mini Din Connector Board from OSHPark (Optional)

8 Pin Mini Din Scart RGB Cable

3x 560 Ohm Resistors

1x TMS9928A Chip

Some wires

A Phillips Head Screwdriver

A decent Soldering Iron

Some Soldering Wires

Desoldering Braid, Pump, or Hakko Desoldering Gun (If you want to do no-cut method)

An OSSC, a Framemeister, a PVM RGB Monitor, or any Scart adapter (Required for RGB)

 

Step 1: Unscrew all of the screws from the bottom of the TI99/4A and then carefully open it.

Step 2: Unplug the power supply from the motherboard and unscrew all of the screws from the motherboard. And don't forget to take off the cartridge connector and take out the RF Shield, as well as the keyboard connector!

Step 3: After you open the RF shield from the motherboard, you will see the TMS9918A Chip, so you need to remove it. If it is socketed, it is very easy to remove it. Then, replace it with the TMS9928A Chip.

Step 4: You need to solder the TMS RGB Board onto the bottom of the VDP Chip like this:

F439F11B-0C40-48DD-B4E9-2C201CD3DD70.jpeg

And solder the wires to the chip:

0F089C84-B350-48B6-8204-081684F78421.jpeg

And don't forget to feed the wire for the audio which is Pin 3 of the TI's Video connector.

Step 5: Solder the three 560 Ohm resistors to those places like those:

Screen Shot 2020-08-25 at 6.02.32 PM.png

Step 6: If you want to do no-cut method, simply desolder the original video connector off from the board and feed all of the wires to the 8 pin mini din connector.

Step 7: Test is to make sure it works before putting the TI back together. (If it works, then move on. But, if it doesn't work, check your work and try again.) Make sure you mount the RGB connector!

Step 8: Carefully put the console back together, and then enjoy!

Edited by Retro_Game_Lover96
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One correction is that the red and blue lines represent jumpers to the DIN connector.  The red line is what you'll find in 9918-based TI's, and the blue line is where a jumper is connected to send component video to the DIN connector.  Changing the jumper lengths is unnecessary.  Only the yellow and green lines need to be resistors.

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3 hours ago, ChildOfCv said:

One correction is that the red and blue lines represent jumpers to the DIN connector.  The red line is what you'll find in 9918-based TI's, and the blue line is where a jumper is connected to send component video to the DIN connector.  Changing the jumper lengths is unnecessary.  Only the yellow and green lines need to be resistors.

Alright

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Nice work.  That output looks great.

 

Can you confirm whether the audio still works on the machine?  I haven't been following the thread closely, but last I saw, the audio subsystem relied on a clock output from the '9918A that isn't there on the '9928A.

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1 hour ago, Falonn said:

Nice work.  That output looks great.

 

Can you confirm whether the audio still works on the machine?  I haven't been following the thread closely, but last I saw, the audio subsystem relied on a clock output from the '9918A that isn't there on the '9928A.

The audio works on my TI while it is connected from the audio pin from the original connector to the 8 pin din mini connector’s pins 1 & 2 because the TI has a mono sound just like the ColecoVision’s.

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4 hours ago, Falonn said:

Nice work.  That output looks great.

 

Can you confirm whether the audio still works on the machine?  I haven't been following the thread closely, but last I saw, the audio subsystem relied on a clock output from the '9918A that isn't there on the '9928A.

It likely depends on board revision.  Some of the audio chips take the clock from the 9918 chip while some take it from the system clock, according to the schematic.  If it has the TMS9919, SN94624, SN76494, or SN76494A, then its clock came from the 9918.  SN76489, SN76489A, SN76496, or SN76496A come from the system clock.

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