Swapping the TMS9929A for the TMS9918A?

[oracle_jedi]

I recently acquired a CGL M5.

 

Its a machine I've wanted since they first came out. I loved the design of the Sord M5, and even though the CGL version doesn't share the Sord's elegant "M5" logo, it wasn't very expensive and allowed me to explore the great "M5 Multi II" multi-game ROM made and sold by Charlie Robson.

 

Now this post may be in the wrong forum. But you guys know TI hardware better than anyone, and the CGL M5 uses the TMS9929A VDP also found in European spec TI99/4As among many other machines. The M5 then converts the R-Y, Y, B-Y output to composite PAL.

 

But my monitor is a North American Commodore 1084, and expects composite NTSC or RGB.

 

I've looked around for a 9929A to RGB conversion schematic, and there are a few, including the one linked in this document from a Sega SC3000 forum:

 

http://www.smspower.org/forums/2325-RYBYYOutputFromSC3000VDPTMS9929

 

But I also see that some people have tried this approach and met with mixed results, including one ColecoVision owner who it seemed may have fried his machine in the effort (see post 26)

 

http://atariage.com/forums/topic/110598-colecovision-av-out/page-2

 

This guy has a neat looking board that it seems would make pulling RGB from the TMS9929A straight forward, and has generously shared all the schematics and build files, but since I have never had a board made before I am way out of my depth on this one:

 

https://hackaday.io/project/13056-tms9929a-rgb-and-component-adapter

 

So another approach might be to convert the CGL M5 to use a TMS9918A instead? Can that be done?

 

From an evening spent looking at websites, it seems I might be able to remove the 9929A and insert the 9918A. Leave pins 35 and 38 NC, and then drive pin 36 directly to the RCA jack.

 

I'd need to replace the oscillator too to get the right color signal for NTSC, and probably burn a Sord NTSC BIOS so that the unit reports itself as NTSC to those games that depend on timing.

 

So how insane is the replacement plan? Would it work in theory? Assuming there isn't something else in the Sord's design that prevents it? Can you tap composite NTSC right off pin 36 of the VDP? What else would I need? Diodes? Resistors?

 

And if these questions are worthy of a face palm, should I just go hunt for a native NTSC Sord model? I can also lug my Sony PVM out of the closet which has PAL and NTSC Composite and S-Video, but doesn't have RGB, so the Amiga and ST displays look awful.

 

Thanks for any pointers.

 

 

 

 

 

[PeteE]

There's a newer ColecoVision RGB mod here. You might have better luck getting a pre-assembled board from someone in that thread, and I like how it attaches to the through pins on the underside of the PCB, but dunno if that will work for the M5. (I've never tried it personally, just thought it looked neat.)

[Tursi]

It's all doable, though. If you do the swap, you might want to bend up the three pins that differ (rather than rely on no side effects from the YCrCb circuitry), and use the composite driver circuit from the datasheet.

 

I replaced the 9918A in a TI with a 9928A to experience with component, and it worked fine in that arrangement. There's a 9919A, apparently, that will preserve your 50Hz interrupt (the 9918A will give you 60Hz). It's probably as uncommon as the 9928A though

[oracle_jedi]

Hey thanks guys.

 

I followed the link that PeteE gave and ordered one of the 9929A to RGB boards from OshPark (well actually the minimum order is 3)

 

I think its just the PCB, so this will be entertaining, but I will try this and see how it goes.