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Retro_Game_Lover96

RGB Mod Explanation

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Hey, I have a TI99 4A computer, a TMS9928ANL chip, a TMS-RGB mod board (the ones I got from Mobius), and an 8 pin mini din connector, so does anyone explain how to install the RGB mod and feed the audio?

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52 minutes ago, Retro_Game_Lover96 said:

I know that, and it is the same thing as the ColecoVision version.

What is unclear?

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The video signals will connect to the DIN the same way they do on the CV.  The audio... you'll have to find out where the TI prepares for final output on that.  Looks like pin 3 of the monitor port will work.

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3 hours ago, ChildOfCv said:

The video signals will connect to the DIN the same way they do on the CV.  The audio... you'll have to find out where the TI prepares for final output on that.  Looks like pin 3 of the monitor port will work.

The pin of TI’s video connector will work for the audio for the RGB mod.

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I can't tell by looking at the pictures, since I don't know which way you flipped the board.  But the square hole goes on pin 1, which is on the same side as the indentation on the chip.

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Welp, I am certainly having the hard times to get this mod working.

 

Despite having the 9918 chip replaced by 9928 chip.

 

UPDATE: The sync is working, but there are no colors.

 

CABAF347-218E-41E0-B7D6-6F7A486B586F.jpeg

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

1D36D115-69DC-4EC5-B183-96D6A908FABA.jpeg

1CCD408B-556A-4842-9F7B-2325D96548D2.jpeg

Edited by Retro_Game_Lover96

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Did you use the same connector and board for this as for the CV?  Did you make all of the same connections?

 

Pins 38 and 35 are the color difference pins.  Make sure they are soldered correctly.  Use flux to touch them up instead of letting it blob like that.

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There's little fibers of wires floating at your solder points. Not good. And that ground is not good looking either, but still may not be the issue.

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I didn't see the details on your post in the Coleco forum - now I understand how it's attached. You're going to need to cut some traces.

 

The three video pins on the 9928 are 35 (B-Y), 36 (Y) and 38 (R-Y). On the 9918, these pins are CPUCLK (38), Composite Video (36) and Ext VDP (35). (I erroneously stated in the other thread that one of them was tied to reset, different issue, not related to this).

 

Anyway, I don't have a console handy to check, but I believe one or both of pins 35 and 38 are connected to something. CPUCLK /is/ used on the 99/4 but not the 4A, so I'm not 100% certain. The 4 schematic says that 35 is not terminated to anything and I do believe that is correct on the 4A as well, so I'd focus first on pin 38.

 

Of course, after checking your wiring for shorts as suggested above - the 'Y' signal is your black and white picture. If that's shorting to the other pins, you'd also get that. ;)

 

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7 hours ago, Tursi said:

I didn't see the details on your post in the Coleco forum - now I understand how it's attached. You're going to need to cut some traces.

 

The three video pins on the 9928 are 35 (B-Y), 36 (Y) and 38 (R-Y). On the 9918, these pins are CPUCLK (38), Composite Video (36) and Ext VDP (35). (I erroneously stated in the other thread that one of them was tied to reset, different issue, not related to this).

 

Anyway, I don't have a console handy to check, but I believe one or both of pins 35 and 38 are connected to something. CPUCLK /is/ used on the 99/4 but not the 4A, so I'm not 100% certain. The 4 schematic says that 35 is not terminated to anything and I do believe that is correct on the 4A as well, so I'd focus first on pin 38.

 

Of course, after checking your wiring for shorts as suggested above - the 'Y' signal is your black and white picture. If that's shorting to the other pins, you'd also get that. ;)

 

Are you sure this’ll work?

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3 hours ago, Retro_Game_Lover96 said:

Where and what are the jumpers W202 and W204 of the TI?

 

1999860282_ScreenShot2020-08-25at6_02_32PM.thumb.png.9c7e99dcda809d9f2a2da5dc4b71de05.png

 

This part appears to be unnecessary after all -- the schematic shows the resistors after the jumper, but the PCB has them before it.  You can skip this particular step:

You will find two bare wires that connect like in the red line.  They go between the hole on the left and the near hole on the right.  It appears that they need to be hooked up like the blue line instead:  From the hole on the left to the hole on the far right.  You'll find them just above a large capacitor on that corner.  

 

Remove the shorter wires and replace them with longer ones to make it to the far holes.

 

 

 

Now there's the yellow line.  That one is apparently a jumper.  Replace it with a 560-ohm resistor.  Then add a 560-ohm resistor at both green lines.

 

 

Edited by ChildOfCv

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The TMS9928 NEEDS load resistors on its color outputs, as you'll see in the data sheet/manual.  So this is not just a shot in the dark.  I can't guarantee 100% that it will work either, since I don't have a TI to test on.  But it is a necessary step.

 

The ColecoVision is already designed around using the 9928, so it already has those load resistors.  The TMS-RGB board was designed with that in mind.  So yeah, you likely need to add some.

 

Now, one potential gotcha is that pin 35 is grounded by the jumper at the yellow line above.  Let's hope it didn't damage the chip when it was trying to output color difference signals straight to ground.

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13 hours ago, Retro_Game_Lover96 said:

So I do need 560 Ohm resistors to make it work.

Why not just try it and then report back if it works or not? ChildOfCv already said that he wasn't 100% sure so you'll need to take the plunge on this.

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I got color out of a 9928 in a 4A console without jumper changes, but it looks like I DID have the resistors in there (using a component to VGA adapter)! The colors were not /correct/, but they were present ;). 

 

image.thumb.png.9d9b68787213da4b545dd64ddec24425.png

 

Not sure why the picture is so bad, probably hiding the awful soldering job. ;)

 

You asked if checking for shorts was going to work - you got something to lose by trying? ;) Even experts sometimes short the pins by accident. 

 

 

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2 hours ago, Tursi said:

I got color out of a 9928 in a 4A console without jumper changes, but it looks like I DID have the resistors in there (using a component to VGA adapter)! The colors were not /correct/, but they were present ;). 

 

image.thumb.png.9d9b68787213da4b545dd64ddec24425.png

 

Not sure why the picture is so bad, probably hiding the awful soldering job. ;)

 

You asked if checking for shorts was going to work - you got something to lose by trying? ;) Even experts sometimes short the pins by accident. 

 

 

How fascinating?

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On 8/26/2020 at 9:13 PM, Retro_Game_Lover96 said:

How fascinating?

Confirming you needed the resistors, duh.

 

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On 8/26/2020 at 6:40 PM, Tursi said:

I got color out of a 9928 in a 4A console without jumper changes, but it looks like I DID have the resistors in there (using a component to VGA adapter)! The colors were not /correct/, but they were present ;). 

Do you think you can attribute the wrong colors to the lack of color burst suppression?  In other words, would you expect the adapter to fix the "wrong color" problem?

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